Petroleum Experts
MBAL
Reservoir Engineering Toolkit
Version 6
April 2001
USER GUIDE
The information in this document is subject to change as major improvements and/or
amendments to the program are generated. When necessary, Petroleum Experts will
issue the proper documentation.
The software described in this manual is furnished under a licence agreement. The
software may be used or copied only in accordance with the terms of the agreement. It
is against the law to copy the software on any medium except as specifically allowed in
the license agreement. No part of this documentation may be reproduced or
transmitted in any form or by any means, electronic or mechanical, including
photocopying, recording, or information storage and retrieval systems for any purpose
other than the purchaser's personal use, unless express written consent has been given
by Petroleum Experts Limited.
All names of companies, wells, persons or products contained in this documentation are
part of a fictitious scenario or scenarios and are used solely to document the use of a
Petroleum Experts product.
Address:
Petroleum Experts Limited
Osborne House
1 Osborne Terrace
Edinburgh
Scotland
EH12 5HG
Tel: (44 131) 474 7030
Fax: (44 131) 474 7031
email: edinburgh@petex.com
Internet: www.petex.com
Registered Office:
Petroleum Experts Limited
Osborne House
1 Osborne Terrace
Edinburgh
Scotland
EH12 5HG
Table of Contents I
Introduction
0-1
About this guide ............................................................................................... 0-1
How to use this guide ...................................................................................... 0-2
Symbols and conventions................................................................................ 0-3
MBAL Installation
1.1
1-1
System Requirements ................................................................................ 1-1
1.1.1 Upgrading from a previous version ....................................................... 1-2
1.2
Installing MBAL........................................................................................... 1-3
1.2.1 Running Setup ...................................................................................... 1-3
1.2.2 The PROSPER.INI File ............................................................................ 1-3
1.3
Starting MBAL............................................................................................. 1-4
1.3.1 Connecting the Software Protection Key .............................................. 1-4
1.3.2 Creating the MBAL Icon ........................................................................ 1-4
1.4
REMOTE Software Utility ........................................................................... 1-5
1.4.1 Entering the user authorisation code .................................................... 1-5
1.4.2 Updating the Software Protection Key .................................................. 1-6
1.5
Program Check List.................................................................................... 1-7
Basic Windows features
2-1
2.1
Accessing MBAL......................................................................................... 2-1
2.2
Parts of a window ....................................................................................... 2-1
2.2.1 Parts of a window.................................................................................. 2-1
2.2.2. The Mouse and Keyboard..................................................................... 2-2
2.2.3 Choosing and selecting items ............................................................... 2-3
Using the MBAL application
3.1
3-1
File Management........................................................................................ 3-1
3.1.1 Opening a File....................................................................................... 3-1
3.1.2 Creating a New File............................................................................... 3-2
3.1.3 Saving a File ......................................................................................... 3-2
3.1.4 Defining the Working Directory ............................................................. 3-3
3.1.5 Preferences........................................................................................... 3-3
3.1.6 Viewing the Software Key ..................................................................... 3-4
3.1.7 Selecting Printers and Plotters.............................................................. 3-4
3.1.8 The Windows Clipboard........................................................................ 3-4
3.1.9 Windows Notepad................................................................................. 3-4
3.2
Setting the System Units ............................................................................ 3-5
Material Balance Program - Version 6
II Table of Contents
3.2.1 Changing the Units System .................................................................. 3-6
3.2.2 Setting Individual Input / Output Units .................................................. 3-7
3.2.3 Saving a Unit System ........................................................................... 3-7
3.2.4 Using the Minimum and Maximum Limits ............................................. 3-7
3.2.5 Generating a Units Report .................................................................... 3-8
3.3
Getting Help ............................................................................................... 3-8
3.3.1 Accessing Help ..................................................................................... 3-8
Data Import
4.1
4-1
Importing Data in MBAL ............................................................................. 4-1
4.1.1 Importing an ASCII File......................................................................... 4-2
4.1.2 Importing data from an ODBC Datasource........................................... 4-4
4.2
Static Import Filter...................................................................................... 4-4
4.3
ASCII File Import........................................................................................ 4-5
4.3.1 Import Set-up........................................................................................ 4-6
4.3.2 Line Filter.............................................................................................. 4-7
4.3.3 Import Filter .......................................................................................... 4-8
4.4
ODBC Database Import ........................................................................... 4-10
4.4.1 Filter Set-up ........................................................................................ 4-10
4.4.2 Choose Table & Fields ....................................................................... 4-11
Plots, Reports
5.1
5-1
The Plot Screen ......................................................................................... 5-1
5.1.1 Resizing the Display ............................................................................. 5-1
5.1.2 Modifying the Plot Display .................................................................... 5-2
5.1.3 Preparing to Plot ................................................................................... 5-4
5.1.4 Making a Hard Copy of the Plot............................................................ 5-5
5.1.5 Changing the plotted variables ............................................................. 5-5
5.2
The Report ................................................................................................. 5-6
5.2.1 Preparing to Print.................................................................................. 5-6
5.2.2 Printing a Report................................................................................... 5-6
5.2.3 Viewing a Report .................................................................................. 5-8
5.2.4 Solving Printing Problems..................................................................... 5-8
Defining the system
6-1
6.1
Reservoir Analysis Tools............................................................................ 6-1
6.2
System Options.......................................................................................... 6-2
April 2001
Table of Contents III
Describing the PVT ............................................................................................. 7-1
7.1
Entering the PVT ........................................................................................ 7-1
7.1.1 PVT Setup ........................................................................................... 7-2
7.1.2 PVT for Oil ............................................................................................ 7-2
7.1.2.1 Controlled Miscibility.................................................................... 7-3
7.1.3 PVT for Gas .......................................................................................... 7-4
7.1.4 PVT for Retrograde Condensate .......................................................... 7-5
7.1.5 Variable PVT for Oil Reservoir .............................................................. 7-6
7.1.6 PVT for General Model ......................................................................... 7-7
7.1.7 Multiple PVT Definitions........................................................................ 7-7
7.2
Matching Correlations ................................................................................ 7-8
7.3
Using PVT tables...................................................................................... 7-10
7.3.1 PVT Tables for Controlled Miscibility .................................................. 7-11
7.4
Checking the PVT calculations................................................................. 7-12
7.4.1 PVT Command Buttons ...................................................................... 7-14
7.5
Fluid Compositions................................................................................... 7-15
7.5.1 Entering the Components ................................................................... 7-15
7.5.1.1
Accentric Factors................................................................... 7-15
7.5.1.2
Composition Command Buttons............................................ 7-16
7.5.2 Binary Coefficients .............................................................................. 7-17
7.5.3 Separator Conditions .......................................................................... 7-18
7.5.4 Phase Envelope.................................................................................. 7-18
7.5.5 Fluid Properties Calculations .............................................................. 7-19
The Material Balance Tool
8.1
8-1
MBAL Graphical Interface........................................................................... 8-4
8.1.1 Manipulating Objects ............................................................................ 8-5
8.1.2 Viewing Objects .................................................................................... 8-7
8.1.3 Validating Object Data .......................................................................... 8-9
8.1.4 Graphical Interface Pop-up Menu ......................................................... 8-9
8.2
Tool Options ............................................................................................. 8-10
8.3
Input ......................................................................................................... 8-14
8.3.1 Well Data ............................................................................................ 8-14
8.3.2 Setup .................................................................................................. 8-14
Material Balance Program - Version 6
IV Table of Contents
8.3.3 Production / Injection History .............................................................. 8-16
8.3.4 Production Allocation .......................................................................... 8-17
8.3.5 Tank Parameters ................................................................................ 8-18
8.3.6 Water Influx ........................................................................................ 8-22
8.3.7 Rock Properties .................................................................................. 8-24
8.3.8 Pore Volume vs Depth........................................................................ 8-25
8.3.9 Relative Permeability .......................................................................... 8-26
8.3.10 Production History .............................................................................. 8-28
8.3.10.1 Entering the Tank Production History.................................... 8-28
8.3.10.2 Calculating the Tank Production History and Pressure ......... 8-29
8.3.10.3 Calculating the Tank Production History Rate Only .............. 8-30
8.3.10.4 Plotting Tank Production History ........................................... 8-31
8.3.11 Production Allocation .......................................................................... 8-32
8.3.12 Transmissibility Data........................................................................... 8-33
8.3.13 Transmissibility Parameters................................................................ 8-33
8.3.14 Transmissibility Production History ..................................................... 8-36
8.3.15 Transmissibility Matching.................................................................... 8-37
8.3.16 Input Summary ................................................................................... 8-39
8.3.17 Input Reports ...................................................................................... 8-39
8.4
History Matching ...................................................................................... 8-39
8.4.1 History Setup ...................................................................................... 8-40
8.4.2. Graphical Method ............................................................................... 8-41
8.4.2.1
Changing the Reservoir and Aquifer Parameters.................. 8-42
8.4.2.2
Straight Line Tool .................................................................. 8-42
8.4.2.3
Calculations Behind the Plot: ................................................ 8-42
8.4.3 Analytical Method ............................................................................... 8-43
8.4.3.1
Regressing on Production History......................................... 8-46
8.4.3.2
History Points Sampling ........................................................ 8-47
8.4.3.3
Changing the Weighting of History Points in the Regression 8-48
8.4.3.4
Calculations Behind the Plot ................................................. 8-49
8.4.4 Energy Plot ......................................................................................... 8-49
8.4.5 WD Plot .............................................................................................. 8-49
8.4.6 Simulation........................................................................................... 8-49
April 2001
8.4.6.1
Running a Simulation ............................................................ 8-50
8.4.6.2
Saving Simulation Results..................................................... 8-52
8.4.6.3
Plotting a Simulation ............................................................. 8-53
Table of Contents V
8.4.7 Fw / Fg / Fo Matching ......................................................................... 8-54
8.4.7.1
Running a Fractional Flow Matching ..................................... 8-56
8.4.8 Sensitivity Analysis.............................................................................. 8-57
8.4.8.1
8.5
Running a Sensitivity ............................................................. 8-58
Production Prediction ............................................................................... 8-58
8.5.1 Prediction Set-up ................................................................................ 8-64
8.5.2 Production and Constraints................................................................. 8-66
8.5.2.1
Voidage Replacement and Injection...................................... 8-69
8.5.3 DCQ Swing Factor (Gas reservoirs only) ............................................ 8-70
8.5.4 DCQ Schedule .................................................................................... 8-71
8.5.5 Well Type Definitions .......................................................................... 8-72
8.5.5.1
Well Type Setup .................................................................... 8-73
8.5.5.2
Well Inflow Performance ....................................................... 8-73
8.5.5.3
Inflow Performance (IPR) Models.......................................... 8-76
8.5.5.4
Multirate Inflow Performance................................................. 8-79
8.5.5.5
Gas Coning Matching ............................................................ 8-79
8.5.5.6
Well Outflow Performance..................................................... 8-81
8.5.5.7
Tubing Performance .............................................................. 8-82
8.5.5.7.1
Constant Bottom Hole pressure ........................................ 8-82
8.5.5.7.2
Tubing Performance Curves ............................................. 8-83
8.5.5.7.3
Cullender Smith correlation ............................................... 8-86
8.5.5.7.4
Witley correlation............................................................... 8-87
8.5.6 Testing the Well Performance ............................................................ 8-89
8.5.7 The Well Schedule.............................................................................. 8-90
8.5.8 The Reporting Schedule ..................................................................... 8-91
8.5.9 Running a Prediction........................................................................... 8-92
8.6
8.5.9.1
Saving Prediction Results...................................................... 8-94
8.5.9.2
Plotting a Production Prediction ............................................ 8-96
8.5.10
Displaying the Tank Results .......................................................... 8-97
8.5.11
Displaying the Well Results ........................................................... 8-97
Compositional Tracking............................................................................ 8-99
8.6.1 Input Data ........................................................................................... 8-99
8.6.2 Operation ............................................................................................ 8-99
8.6.3 What is MBAL Calculating? .............................................................. 8-100
Material Balance Program - Version 6
VI Table of Contents
Monte-Carlo Technique
9-1
9.1
Tool Options............................................................................................... 9-3
9.2
Distributions ............................................................................................... 9-4
Decline Curve Analysis
10-1
10.1
Tool Options............................................................................................. 10-1
10.2
Production History.................................................................................... 10-2
10.3
Matching the Decline Curve ..................................................................... 10-5
10.4
Prediction Set-up ..................................................................................... 10-7
10.5
Reporting Schedule ................................................................................. 10-8
10.6
Running a Production Prediction.............................................................. 10-9
1D Model
11-1
11.1
Programme Functions:............................................................................. 11-1
11.2
Technical Background: ............................................................................ 11-1
11.3
Tool Options............................................................................................. 11-3
11.4
Reservoir and Fluids Properties............................................................... 11-4
11.5
Relative Permeability ............................................................................... 11-6
11.6
Running a Simulation ............................................................................... 11-8
11.6.1
Plotting a simulation......................................................................... 11-9
Multi Layer Tool
12-1
12.1
Programme Functions:............................................................................. 12-1
12.2
Technical Background: ............................................................................ 12-1
12.3
Tool Options............................................................................................. 12-3
12.4
Layer Properties....................................................................................... 12-4
12.4.1
12.5
Relative Permeability ..................................................................... 12-5
Running a Calculation .............................................................................. 12-6
Examples
A-1
A.1
Water Drive Oil Reservoir .......................................................................... A-1
A.2
Forward Prediction ..................................................................................... A-8
A.3
Other Example Files .................................................................................. A-19
References
April 2001
B-1
Table of Contents VII
MBAL Equations
C.1
C-1
Material Balance Equations........................................................................C-1
C.1.1 OIL: .......................................................................................................C-1
C.1.2 GAS: .....................................................................................................C-2
C.1.3 OGIP Calculations: ...............................................................................C-2
C.1.4 Natural Depletion Reservoirs: ...............................................................C-2
C.1.5 Abnormally Pressured Reservoirs:........................................................C-2
C.1.6 Water Drive Reservoirs:........................................................................C-3
C.2
Aquifer Models ...........................................................................................C-4
C.2.1 Small Pot...............................................................................................C-4
C.2.2 Schilthuis Steady State .........................................................................C-4
C.2.3 Hurst Steady State................................................................................C-5
C.2.4 Hurst-van Everdingen-Dake..................................................................C-6
C.2.5 Hurst-van Everdingen-Odeh .................................................................C-8
C.2.6 Vogt-Wang............................................................................................C-9
C.2.7 Fetkovitch Semi Steady State ...............................................................C-9
C.2.8 Fetkovitch Steady State ......................................................................C-11
C.2.9 Hurst-van Everdingen Modified...........................................................C-12
C.2.10 Carter-Tracy .....................................................................................C-13
C.3
Relative Permeability................................................................................C-14
C.3.1 Corey Relative Permeability Function : ..............................................C-14
C.3.2 Stone method 1 modification to the Relative Permeability Function: .C-14
C.3.3 Stone method 2 modification to the Relative Permeability Function: .C-15
C.4
Nomenclature: ..........................................................................................C-16
C.4.1 Subscripts ...........................................................................................C-18
Trouble Shooting Guide
D-1
D.1
Prediction not Meeting Constraints ............................................................D-1
D.2
Production Prediction Fails.........................................................................D-1
D.3
Pressures in the Prediction are Increasing (With No Injection) ..................D-2
D.4
Reversal in the Analytic Plot.......................................................................D-2
D.5
Difference between History Simulation and Analytic Plot...........................D-2
D.6
Dialogs Are Not Displayed Correctly ..........................................................D-3
Material Balance Program - Version 6
Introduction
This user guide is designed to introduce you to the features of the MBAL
program.
This document explains the basic procedures to run case studies using the
examples provided. This user guide focuses on how to use the program features
as analytical tools. The guide is not a reference manual, and does not provide
technical information on the program 's methodology.
About this guide
The guide assumes you are familiar with basic Windows operations and
terminology. The screen displays used in this guide are taken from the
examples provided with the software. On occasion, the data files may vary from
the examples shown as updates to the program are issued. Where major
amendments or changes to the program require further explanation, the
corresponding documentation will be provided.
What is in this guide
The chapters in this document are organised to correspond with the steps you
need to take to work with the MBAL application, define your objectives and make
an analysis.
•
Chapter 1, "MBAL Installation," describes the hardware and software you need
to run the program, how to install the program and start the application.
• Chapter 2, "Basic Windows Features," for users unfamiliar with Windows
basics this chapter briefly describes the different parts of a window, mouse and
keyboard techniques as well as how to get help in MBAL.
•
Chapter 3, "Using the MBAL application," explains how to open, save and print
files, enter and edit values in the fields, customise your work space and
describes the MBAL command buttons.
•
Chapter 4, "Importing Data," describes the program import and data transfer
facilities. It explains how to read data from different sources : ASCII files and
ODBC compatible databases.
•
Chapter 5, "Plotting and printing results," describes the program plot and
report facilities. It explains how to change the aesthetics and print a plot display.
This chapter also describes the report dialogue box and explains how to set up a
printer and prepare to print.
•
Chapter 6, "Defining the System," describes the parameters that define the
conditions and intended use of the MBAL program.
Introduction
Intro-2
•
Chapter 7, "Describing the PVT," explains the data input screens used to
describe the properties of the reservoir fluid. This data is then used to calculate
the regression and flow calculations.
•
Chapter 8, "The Material Balance Tool," explains the input screens and
processing steps to take when selecting 'Material Balance' as a reservoir analysis
tool.
•
Chapter 9, "Monte-Carlo analysis," explains the input screens and procedures
required for using the 'Monte-Carlo' option as a reservoir analysis tool.
•
Chapter 10, "Decline Curve analysis," explains the input screens and
procedures required for using the 'Decline Curve' option as a reservoir analysis
tool.
•
Chapter 11, "1D Modelling," explains the input screens and procedures
required for using the '1D Model' option as a reservoir analysis tool.
•
Chapter 12, "Multi Layer," explains the input screens and procedures required
for using the 'Multi Layer' option as a reservoir analysis tool.
• Appendix A, "MBAL Examples," to help you become familiar with the software
and program options 3 worked examples are provided. We suggest you run
through the examples to get a feel for the program.
•
Appendix B, "MBAL References," documents the source references (technical
papers and books) used in the development of the program.
• Appendix C, "MBAL Equations," shows some of the equations used in the
program.
•
Appendix D, "Trouble Shooting Guide," gives solutions to some problems
commonly encountered by users.
How to use this guide
Depending on your needs and the amount time you want to spend becoming
familiar with the program, this guide is arranged to be used in the following
ways:
Beginning-to-end
If you are new to Windows applications, we recommend you read this guide to
the end to become familiar with the program features, menus, and options.
This is the slow approach, but will cover all you need to know about the
program.
Petroleum Experts
Introduction
Intro-3
Selected tasks
Use this approach only if you are already familiar with the facilities available in
the program, or if you only wish to use a particular analysis tool (e.g. MonteCarlo).
Worked examples
If you are limited with time and want to sample the program features quickly,
follow the instructions provided with the examples in Appendix A. These will
show how to run a quick analysis trying each feature for a particular case.
Symbols and conventions
Throughout the user guide, special fonts and/or icons are used to demonstrate
specific steps, instructions and procedures in the program.
ALL CAPS
Represent DOS directories, file names, and commands.
Italics
Used to highlight certain points of information.
Keycap
Bold italics are used to indicate a specific action to be taken.
For example: "Click Done to exit the window."
Menu
Command
To avoid repeating the phrase "Click the File menu and
choose the Open command," we use the File
Open
convention instead.
Emphasises specific information to be entered or aware of.
➲
April 2001
Step-by step instructions are marked by this keyboard icon.
This symbol is a reminder to click the RIGHT mouse button.
Clicking the right mouse button, performs specific functions in
MBAL, depending on the active dialogue box or plot. If you do
not have a right mouse button, holding down the SHIFT key
while you click the mouse button performs the required
function.
Material Balance Program - Version 6
MBAL Installation
This chapter explains how to install MBAL on your computer. The guide assumes
you have a working knowledge of Windows terms and procedures. If you are
unfamiliar with the Windows operating system, we recommend you read the relevant
sections in the Microsoft Windows User's Guide to learn more about Windows
operations.
This chapter gives instructions on installing the program to a Windows 95, 98, 2000
or Windows NT operating system.
1.1 Software and Hardware Requirements
The program supports all Windows-certified device drivers that are shipped with
Windows. The list of devices, software and hardware supported by Windows is
included with the documentation of your copy of Windows.
MBAL can be run as single User licence or on a Network. In either case, a special
security key is needed. The security key is called Bitlock for stand-alone licences
and Hardlock for network licences
The security key is provided by Petroleum Experts.
The minimum requirement recommended for MBAL is Pentium 450 MHz machine
with 128 Mbytes.
In order to install the software from the CD, the machine should have access to a CD
drive.
For a stand-alone licence, a security key (Bitlock) provided by Petroleum Experts
must be attached to the parallel printer port of the PC before MBAL can be run.
For network installation, the security key (Hardlock) can be attached to any PC
communicating with the network.
You should refer to the separate installation procedure for network Hardlock sent
with the purchase of a Hardlock licence.
If MBAL has been installed for the first time on a machine, the Bitlock driver must be
installed on this machine in order to establish the link between the software and the
security key (Bitlock driver).
In order to install the Bitlock driver, you will have to start from the main Windows
screen. Here you click on |Start |Programs |Petroleum Experts IPM |Utilities and then
start the “Set-up Bitlock Driver”.
This will prompt the following screen.
Chapter 1 MBAL Installation
1-2
Section I
From the screen above, you will have to run the |Functions |Install Sentinel Driver |
OK.
You might need to modify the path of the sentinel files.
You should ensure that you have the permission to install a driver.
Your IT manager can help you getting the required permission.
1.1.1 Upgrading from a Previous Version
For convenience in running linked models, Petroleum Experts software products now
installs by default into a common sub-directory \Program Files \Petroleum
Experts\IPM X.Y. To avoid the potential for conflicts between program and DLL
versions, it is recommended to install GAP, MBAL and PROSPER in the same
directory.
If you wish to keep an original version of the program, back it up into another
directory before installing the upgrade.
Â
All program upgrades are backward compatible. This ensures that data files
created with earlier versions of the program can still be read by later program
versions. However, if you save a data file with the new version, that file can
Petroleum Experts
Chapter 1
no longer be opened by earlier versions!
installations, always back up your MBAL files.
MBAL Installation
1-3
As with all new software
1.2 Installing MBAL
Before installing the program on your computer, you should first determine:
•
•
•
The drive where the program is to be installed
The amount of space available on the selected drive
When installing on a network, verify you have the necessary access rights to
create directories and files on the designated volume.
What Set-up does
The installation procedure:
Creates a program directory on your hard disk.
Creates a sample files sub directory on your hard disk.
Unpacks the MBAL program and related files to the selected drive and
directory.
• Creates a program initialisation file PROSPER.INI in your Windows directory.
• Creates a new Windows program group and icon for both MBAL and
REMOTE.
•
•
•
If you are updating MBAL, the set-up can be used to modify, repair or remove
components of the IPM suite. In this case, follow the online instructions
Â
To avoid potential system resources conflicts, please shut down other
applications before running SETUP. Some anti-Virus programs can interfere
with the installation process and may need to be shut down
1.2.1 Running Setup
To install the MBAL program:
1. Insert the program installation CD in the correct drive.
2. From the main screen of Windows, click on |Start |Run and follow the online
instructions.
The option “Repair” is recommended.
1.2.2 The PROSPER.INI file
The PROSPER initialisation file contains the settings you use to customise the
MBAL application environment. Settings such as the program data directory,
customised units system, last file accessed and the colour settings of your screen
graphics are all stored in this file. You do not need to manually modify the
PROSPER.INI file. The program will automatically record any changes to the
settings.
April 2001
Material Balance Program Version 6
1-4
Section I
MBAL automatically creates the PROSPER.INI file in the Windows default directory
using the program's default settings. The location of this file is defined by this entry
in your WIN.INI file:
[PETROLEUM EXPERTS]
IniPath=PROSPER.INI
We do not recommend changing the location of the PROSPER.INI file. If however,
you want to do so for specific reasons (to place it on a specific network drive), take
the following steps:
1. First copy the existing PROSPER.INI file to the required directory.
example:
For
COPY C:\WINDOWS\PROSPER.INI
U:\NETWORK\APPS\MBAL\PROSPER.INI
2. Next amend the 'IniPath' entry in WIN.INI to correspond to the new directory
and path where the PROSPER.INI is now located. e.g.:
IniPath=U:\NETWORK\APPS\MBAL\PROSPER.INI
During the installation MBAL unpacks a number of files onto your computer in the
specified installation directory. The unpacked files should not be modified, removed
or moved to another directory.
1.3 Starting MBAL
Before starting the program, make sure the software protection Bitlock (dongle) is
connected to your PC and that the Bitlock Driver has been installed.
1.3.1 Connecting The Software Protection Bitlock
The software protection Bitlock must be attached to the PARALLEL printer port. Do
Not connect the Bitlock to a serial port, as this can damage the Bitlock or your PC. If
you are using protection Bitlocks for other software, we do not recommend stacking
the Bitlocks. We suggest using only the correct Bitlock with the appropriate
software. Stacking Bitlocks may lead to incompatibilities between Bitlocks, and may
cause read/write or access errors with some Bitlocks.
1.3.2 Creating the MBAL Icon
The MBAL icon should appear automatically in the correct folder under the
Programs menu after installation.
If this does not happen, invoke the Start menu and select Settings | Taskbar.
Select the Start Menu Programs tab and click on Add to add the MBAL program to
the menu. Follow the instructions on the screen.
Petroleum Experts
Chapter 1
MBAL Installation
1-5
To start the program subsequently, select the MBAL program from the programs
menu of the Start menu.
It is also possible to create a shortcut to MBAL on the main Windows desktop. To
do this, click the right hand mouse button anywhere within the desktop and select
New | Shortcut from the resulting popup menu. Follow the instructions on the
screen to create the shortcut to MBAL.EXE.
MBAL can then be executed by double-clicking on the shortcut icon.
1.4 REMOTE Software Utility
All Petroleum Experts' software requires a software protection device to allow it run.
The utility program REMOTE.EXE provided with our software allows you to access
the software protection device to view information such as the enabled program
options, program expiry date(s), and Bitlock number.
You may have been sent an inactive software device. For security, authorisation
codes are always sent separately to the Bitlock. On receiving the software package,
we ask that you contact us to confirm reception. We will then verify the user access
code programmed on your Bitlock, and issue a set of codes to activate the Bitlock.
In these situations, the necessary codes will be sent to you by facsimile, letter or
email.
To enter the codes, you will need to run the REMOTE application installed with
MBAL (see next section for more details).
You can also create a shortcut to the Remote application from the Windows desktop.
For this, click on |New |Short cut anywhere on the Windows screen and follow the
online instruction. The program file is called REMOTE.EXE.
1.4.1 Entering the User Authorisation Code
You enter user authorisation codes only if:
•
The software protection Bitlock you have received is inactive,
•
Access period for the program has expired, or
•
You have acquired new program options
To enter authorisation codes take the following steps:
1)
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Double click the REMOTE icon (or select the REMOTE program from the
Programs menu of Windows 98). A screen similar to the following will appear:
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Figure 2.1:
REMOTE Software
Utility
Bitlock
If your software protection Bitlock is already active, a list of enabled programs will
appear in the Remote screen as above. If MBAL has already been enabled, no
further action is needed. If this is the case, exit the Remote Utility program now. No
user authorisation code is required.
If the code has expired or has not been enabled, the Bitlock should be activated with
the set of codes provided by Petroleum Experts. To do so, you click on the |Update
button on the bottom of the previous screen and the following screen will appear:
Figure 2.2:
Authorisation
Entry screen
Codes
Enter the codes from Left to Right beginning with the top row (you may use <Tab> to
move between the items). Press |Continue to activate the codes. You will then be
returned to the 'Remote Software Bitlock Utility' screen. If you have received
authorisation codes for more than one program, click 'Update Software Bitlock'
again, and enter the codes for the next program.
1.4.2 Updating the Software Protection Bitlock
Access to the software ceases automatically when the license expiry date elapses.
You are, however, reminded several days in advance. This gives you sufficient time
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to contact Petroleum Experts about new codes. Software Bitlocks require updating
when:
• The software license period has ended.
• The annual maintenance fee is due.
Software protection Bitlocks also needs updating when you acquire other Petroleum
Experts software packages. The procedure to update the Bitlock is the same as for
entering the authorisation codes. When the appropriate screen appears, enter the
codes provided - from left to right beginning with the top row. Press OK to activate
the codes, or Cancel to quit the update. To view the expiry date for any of the listed
programs, simply click (highlight) the software name.
Â
Perpetual licence holders will be sent on yearly basis an utility program written by
Petroleum Experts, that automatically updates the Bitlock. The update is hardcoded inside the utility program. step-by-step instructions are sent with this utility
program.
1.5 Program Check List
To ensure trouble free processing and access to the MBAL program, please check:
•
You have sufficient disk space.
•
The software protection Bitlock is connected to your Parallel printer port. Do
Not connect the Bitlock to the serial port, as this can damage the Bitlock or
your PC
•
The software protection Bitlock is firmly in place ensuring a good connection.
If the Bitlock is loose the program may not be able to access the dongle to
activate the program.
•
The printer cable is firmly attached to the software Bitlock. Your printer should
be turned ON and be put on-line.
•
The PC system date is set correctly to the current date (i.e. today's date).
•
You back up your files on a regular basis with disk utility programs. This could
help to avoid the corruption of files, or help detect potential problems with your
hard disk before it is too late. MBAL has a file compression feature that
allows the User to compress/decompress an entire network model with all
associated files (|File |Archive |Create and follow the online instructions).
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Basic Windows features
If you are not familiar with the Windows operating environment, we suggest you read
the Microsoft Windows User's Guide, "Basic Skills" chapter to learn the fundamentals
of using Windows. If you are short of time or a Windows manual is not available, this
chapter provides sufficient information to start you working with MBAL program.
Although a basic knowledge of Windows is an advantage, it is not a prerequisite to
using the program.
2.1 Accessing MBAL
Before you can begin using the program, both Microsoft Windows and MBAL must be
installed on your computer. To install Windows, please contact a member of your data
processing department, or refer to the Microsoft Windows Installation Guide. To install
MBAL, refer to Chapter 1, "MBAL Installation," for instructions.
If the auto reload setting is switched on, when you start MBAL, the program will
automatically open the last file accessed. The file name is stored in PROSPER.INI and
is updated each time you open a file. The time it takes the program to load depends
on the speed of your computer.
2.2 Parts of a window
This section explains some of the basic elements of an application window.
2.2.1
Parts of a window
The following paragraphs describe a basic MBAL application window.
Figure 2.1:
Parts of a Window
Control-Menu Box
The Control-menu box, located in the upper left corner of a window lets you to move,
re-size and close a window or switch to another application. To open the control-menu
box use the mouse and click the box open or press ALT Spacebar.
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Title Bar
The title bar indicates the name of the application followed by the directory path and
name of your open file. The title bar will display (Untitled) after the application name
when no file is open or the file you are creating has not been saved.
Menu Bar
The menu bar lists the menu items available in MBAL. When you select a menu name,
a list of that menu's commands are displayed. A command is an instruction to MBAL to
perform a specific action.
Minimise/Maximise Buttons
These buttons are located in the upper right corner of your window. The Minimise
button reduces the window to an icon on the desktop, while the Maximise button
enlarges the window to fill the entire screen. When a window is maximised, the
Restore button (which contains both up and down arrows) replaces the Maximise
button. The Restore button, or Restore command in the control-menu box, will
reinstate the window to its previous size and position. To minimise a window using the
keyboard, press ALT Spacebar N. To maximise a window press ALT Spacebar X.
Close Button
This button is used to close MBAL. This has the same effect as selecting File – Exit.
2.2.2 The Mouse and Keyboard
This section briefly describes some of the basic techniques you will need to move
around the windows.
Using the mouse
The mouse controls a white arrow shaped pointer on the screen which allows you to
select menu commands, data entry fields or items from drop down list boxes. To move
the pointer, slide the mouse over a flat surface in the direction you want the pointer to
go. Do not press the mouse buttons when you move the mouse. If you run out of
room while moving the mouse, pick up the mouse and place it down again. The pointer
does not move on the screen while the mouse is in the air.
The mouse as a general rule has 2 buttons. The LEFT mouse button is the one
normally used in the techniques of pointing clicking and dragging in Windows. If you
are left-handed for example the functions for the left and right mouse buttons can be
swapped to make it easier to operate. The mouse clicking speed can also be
customised to suit individual preferences.
Check - means positioning the pointer on a check box and pressing the LEFT mouse
button to select a value option or dialogue box.
Point - means to move the mouse pointer and place it over an item on the screen.
This method is used to pick menus or input fields.
Click - to point to an item on the screen the quickly press and release the LEFT mouse
button. This method is used to select menus, entry fields or list options. Selected
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items are highlighted and/or surrounded by a dotted rectangle. When used in selecting
command buttons, clicking will activate the procedure indicated (e.g. Calculate).
Double-click - or quickly pressing the mouse button twice is also a convenient shortcut
for many tasks. Double-clicking should be used with caution, as it may have different
effects from one window to the next.
Drag - to hold the mouse button as you move the mouse in any direction across the
screen. This method is used in the plot screens where areas of interest can be
magnified for a closer view.
Using the Keyboard
The keyboard is another way of effectively moving around windows or executing
commands in MBAL. As you work with the program you will notice that all menus,
menu items and command buttons have a single letter underlined.
These are activated by using the ALT key followed by the underlined letter. For
example, to execute the Save command in the File menu, press ALT F S. Commands
can also be executed by using a combination of keys or shortcuts, for example Ctrl+O.
These combinations are always listed to the right of a menu item and eliminate the
need selecting a command via a menu.
While you proceed through the menus, you will see that some of the menus items
appear dimmed and several have ellipses (....) or black triangles after their names.
These are Windows menu conventions.
Dimmed menu items - indicate the options are not available at this time. It usually
means you have to enter something before you can use the option, or this option
cannot be used with your application.
Ellipses (...) - after menu item indicates a screen will appear when the menu or
command button is chosen. You will be required to make a selection before the
program can carry out the command.
Black Triangles - after a menu item indicates additional options are available.
2.2.3 Choosing and selecting items
Once a menu is displayed, menu items can be selected by either using the mouse to
click the item name, typing the underlined letter of the item name or using the
directional arrow keys. The following describe some useful keys which accomplish
much of the same functions as the mouse.
Arrow Keys - The collective name for the directional ↑, ↓, ← and → arrow keys.
These keys cannot be used to move between data entry fields, but the ↑ and ↓ arrow
keys are useful to view the selections in the drop-down list boxes. The keys move you
forward or back one row at a time. To display the contents of a list box, press ALT ↓.
Enter or ↵ - Once an item has been selected the ↵ key activates the command. A
selected item is usually highlighted, shadowed and/or surrounded by a dotted
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rectangle. This key should not be used for selecting items from list boxes as it will exit
you from the window. To make a selection from a list and close the list box, use the
TAB key.
Esc - This key cancels the current selected menu or quits the current screen display.
Del or Delete - The Del key on the numeric key pad and Delete key on extended
keyboards erases the entire contents of a data entry field. The alternative Backspace (
←) key located next to the top row of numbers on the keyboard can also be used.
These keys do not delete selections in list boxes.
Tab and Back tab - This key moves the insertion point forward to the next field or
backward to the previous field. Any data that is currently in the field will not be
changed. To back tab press the SHIFT and tab keys together.
PgUp/ PgDown and Home / End - Moves forward or back a screen page at a time.
These keys are useful for viewing the selections in list boxes. The Home and End keys
move you to the very top or bottom of a list box.
First Letter - Lets you select an item in the list boxes. Simply type the first letter of
your choice (e.g. T for Temperature) and the program will highlight the first item that
begins with that letter. If more than one item begins with the same letter, type the letter
again to select the next item.
List boxes
List boxes or combination boxes are columns of selections listing correlations or
parameters that can be chosen for your application. Fields where more than one
choice is offered are indicated by an underlined arrow to the right of the entry. To
display the available choices point and click on the arrow or press ALT ↓. The currently
selected (default) item will be highlighted in the list box. Only one item from the list can
be selected at a time.
If there are more choices than can fit in the list box, the complete list can be viewed by
using the scroll bar to the right of the box. To move within the box, drag the scrolling
thumb in the direction required or use the ↑ and ↓ directional arrows.
Smart data input feature
The MBAL program uses a smart data input feature that simplifies the process of
entering data by confining the entry fields to what is relevant for your application. This
feature automatically takes effect when you select the analysis tool and define the
MBAL system options .
Since the analysis tool and system options you select determine the menus, options
and input fields you later have access to, the choices you make must be made with
care. Your selections can be changed at any time; however, always remember new
choices require different data to be supplied and in some instances recalculated.
Closing Nested Dialogs
The MBAL program often has nested dialogs i.e. dialog boxes that are displayed by
clicking buttons on other dialogs. Normally when you left - click the Done button on a
dialog, it will close down that dialog but keep the parent dialog open. However if you
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right - click the Done button on a nested dialog, it will close that dialog and all the
parent dialogs so that you will be returned to the main MBAL window.
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Using the MBAL application
For first time users, this chapter covers the essential features of data management. In
addition to the MBAL procedures used to open files save and print files, this chapter
also describes the procedures to establish links to other Windows programs, define the
system units and getting help. The options and procedures discussed in the following
sections are found under the File, Units, and Help menus.
If you do not have a mouse, please review Chapter 2, "Basic Windows features," for
keyboard equivalents to Windows mouse operations.
3.1 File Management
The following sections describe the File menu commands.
3.1.1 Opening a File
When you first start MBAL, the program automatically opens the last file accessed. If
you do not want to work with this file, other data files can be opened quickly and easily
at any time during the current working session. To open a file, choose File - Open, or
press Ctrl+O. The following screen is displayed:
Figure 3.1:
MBAL- Open File
A dialog box appears listing in alphabetical order, the available files matching your
selection criteria. The files in the default data directory are automatically shown first.
To open a file, use any one of the following procedures:
•
Type in the complete name of the MBAL file in the File Name box, and press
Enter.
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•
Click the File Name box, type the first letter of the filename and press Enter.
the Tab key to move to the Files selection box, next use the ↓ arrow key to
highlight the file you want and press Enter.
• Use
•
Double-click on the file name.
If the file you want is not listed, it is possible that:
1) the file is in a different sub directory,
2) the file is on a different drive, or
3) the file is of a different file type.
The standard MBAL file type is the MBI file. This type is displayed by default. The only
other file type is the MBR file. The only use of this type of file is as an output file from
GAP which stores the results from a GAP prediction that can be read by MBAL.
3.1.2 Creating a New File
While working with MBAL, new data files can be created at any time. To create a new
file choose File - New, or press Ctrl+N. The program clears the MBAL application
screen, title bar, and reinitialises the program input/output data.
3.1.3 Saving a File
When files are opened in MBAL, a copy of the selected file is stored in computer
memory. Any changes to the file are made to the copy in memory. In the event of a
power failure or a computer hanging up, these changes are completely lost. To
maintain your work, we recommend saving your data on a regular basis. This simple
procedure could potentially prevent hours of work and analysis being lost.
To save a file, choose either File - Save or File - Save As, or press Ctrl+S or Ctrl+A.
The Save command stores changes made to the current active file overwriting the
previous data. By default, the Save command saves a file under its original name and
to the drive and directory last selected. If you want to save the file in a different
directory, select the new directory and press Done.
Copying files
Use Save As command to make more than one copy or version of a file. As you work
with the program, the File - Save As command is useful for saving trial runs of your
work. This command allows you to save a file under the same name but to a different
drive, or under a different name on the same drive. Before saving a copy to another
disk or medium, we recommend the original file is first saved on your hard disk.
When copying a file, the default data directory is automatically displayed first. If you
enter a Save As filename that already exists, the program asks if you want to replace
the file. You can choose Yes to replace the existing file or No to select a new name. To
copy a file, enter a new name in the File Name field and press Enter or click Done.
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3.1.4 Defining the Working Directory
The Data Directory option allows you to specify the default working directory. This
facility makes it more efficient to access your data files. Whenever you open, close or
create new files, the program automatically selects the files or saves to the directory
defined in this option.
3.1.5 Preferences
The preferences option allows you to set various MBal preferences. These include:Compress Data Files
Select Yes to compress (zip) data files when saving to disk. This facility is useful for
managing very large data files.
Screen Resolution
Changes the resolution of your screen display. This option is program (MBAL) specific.
The changed settings are temporary and not saved when you close a file or exit the
program. Use this option is useful where you have a large number of wells/tanks in
your data file and wish to see them all displayed on the screen. Your monitor and
display adapter determine whether you can change the screen resolution. Refer to
your computer hardware guide for more information.
Dialog Font
Changes the screen display font type and size. Only fonts installed under Windows are
displayed. Refer to your Windows manual for more information on installing fonts.
Format Numerical Input Fields
This option specifies how the numerical input fields are displayed.
If this is set to Yes, numbers will be displayed with a fixed number of digits e.g. 0.3000
or 12.00. Also the number is centered within the field.
If this option is set to No, numbers will be displayed with as few digits as necessary e.g.
0.3 or 12. Also the number is left justified within the field.
Reload Last File Used at Startup
If you select Yes, MBal will load the file that was in use the last time you ran MBal. If
you select No, MBal will not load any file when it starts.
File History List Length
The file menu normally keeps a list of the last files that were accessed by MBal. This
entry allows you to control the number of files which appears in this list. The maximum
number of files is 10.
Display Results During Calcs.
If you select No, MBal will not update the dialogs with the results until the end of the
prediction and simulation calculations. This will mean that you can not see the progress
of the calculation. However, it will speed up the calculations by up to 25%.
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IPR/VLP Tolerance
This value can be used to control the tolerance used in calculation of VLP/IPR
intersections. The tolerance used in the calculation is the average layer pressure
multiplied by the value displayed in this field. For example, if you enter 0.001 then the
tolerance used will be 0.1% of the average layer pressure.
The default value of 0.001 will handle calculate most intersections accurately and keep
calculation times at a reasonable level. However some cases (particularly with high PIs)
may give poor results - in these cases a smaller tolerance may give better results
although the calculations will be slower.
3.1.6 Viewing the Software Key
The Software Protection command activates the REMOTE software utility program
that allows you to access the software protection key. The REMOTE facility indicates
what programs are enabled on the key, the program expiration date, the key and client
number. This utility is also used to activate the key when the program licence has date
has expired, or update the key when more program modules are acquired. For
information on accessing the REMOTE utility, please refer to Chapter 1, "MBAL
installation".
3.1.7 Selecting Printers and Plotters
Use these menu options to select your output (printer or plotter) devices. For more
information about this menu option, please refer to Chapter 4, "Plotting and printing
results".
3.1.8 The Windows Clipboard
The Clipboard command gives you access to the Windows clipboard where you can
view, save, retrieve or delete data that has been copied or pasted into the clipboard
from another Windows application. This command option can be used to view data
from MBAL calculations that you do not intend to print.
3.1.9 Windows Notepad
The Notepad command gives you direct access to the Windows text editor. This
application is useful to make notes of your current analysis for later inclusion in reports.
This option can also be used view the results of calculations that have been saved to a
file. For more information on reports, please refer to Chapter 5, "Plotting and printing
results".
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Chapter 3 - Using the MBAL Application 3-5
3.2 Setting the System Units
Use the Units menu to define the measurement units that are used in dialog boxes,
calculation output, reports and plots.
•
Units can be defined for each measurement type in the program. Examples of a
measurement type are pressure, density and compressibility.
•
Each measurement type has a set of possible units which can be selected by
the user e.g. pressure can be psia, psig, bar, kPa etc. A different unit can be
selected for input and output for each measurement type. Input units are used
for any value in a dialog that is input by the user. Output units are used for
reports and plots of input data as well as any calculated value on dialogs, plots
or reports.
•
Each measurement type can appear in several places in the program e.g.
pressure is used in the tank setup, production data and prediction output.
•
More than one measurement type can use the same set of possible units (e.g.
gas production and gas injection) but it is useful to have them as separate
measurement types as we may require different units selected for each.
•
A units system is made up of a unit selection for each measurement type in the
program. Four unit systems are supplied with MBAL. These are Oilfield,
Canadian S.I., Norwegian S.I. and German S.I.. You can change the units
selection of all measurement types at once be changing the units system. It is
also possible to create and save your own units systems.
•
The current units selections are saved with each file. So if you change the
units selection, you must save the MBI file or the units selection will be
lost when you open a new file or exit MBAL. Note however that if you select
File-New, it will not reset the units selection so the same selection can be
applied to your next data set.
•
A maximum and minimum validation range can be entered for each
measurement type. Unlike the units selection, the validation range is not
associated with the MBI file. Any change to the range will remain in force until
you exit the program. If you save the range as the default then it will remain in
force until you change it again.
•
To access the Units menu, click the menu name or press ALT U. The following dialog
box appears:
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Figure 3.2:
MBAL Units Definition
The middle of the three columns lists the different measurement types. The input and
output columns show the currently selected unit for each measurement type.
The majority of users are happy to use one of the supplied units systems in which case
you will only need to know how to change and apply the units system.
If you want to use a set of units similar to one of the predefined units systems but with
some modifications, the process is as follows:•
•
•
Select the unit system nearest to the units selection you want to use.
Modify the input and output units selection for any measurement types that you
wish to change.
Save the units selection as a units system so it can be used in the future.
3.2.1 Changing the Units System
The current input/output unit system is shown in the combo box at the bottom of the
column of input and output units. To change to a new units system, simply change the
selection in the combo boxes. This will change the units selection for all the
measurement types to the ones defined for that unit system. For example, if you
change to the oilfield units system it will change the units selection for all the
measurement types to oilfield units.
Make sure that you have the correct units system for both the input and output units.
If you have changed units systems and you wish to keep this setting then you must
save the current MBI file before exiting MBAL or opening another data file. Otherwise
the new setting will be lost.
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Chapter 3 - Using the MBAL Application 3-7
3.2.2 Setting Individual Input / Output Units
Once you have selected your units system you can change a unit selection for an
individual measurement type. This is done by clicking the field in the input/output
column next to the measurement type that you want to change. This will change the
field in the input/output column to a combo box which allows you to change to one of
the other units in the list. Note also that clicking on the input/output column will display
the multiplier and shift for the selected unit and measurement type.
Make sure that you have the correct units system for both the input and output units.
As for the units system, if you have changed the units selection and you wish to keep
this setting then you must save the current MBI file before exiting MBAL or opening
another data file. Otherwise the new settings will be lost.
3.2.3
Saving a Unit System
Once you have been through the process of setting a new units system and changing
the units selection on some individual measurement type, it is wise to save these
settings as a new units system. This means that you can use these settings on other
data files.
To do this, simply click on the Save As button and then enter a name for the new units
system. The new system will appear in the list of units systems.
Also you may wish to modify a previously created units system and save the changes
to the units system. To do this first select the units system you wish to change. Then
make your changes to the units selections for the individual measurement types as
described above. Finally click the Save button to save the changes.
If the Save button is disabled then you may trying to save a predefined units system
(e.g. oilfield) which is not allowed. In this case, use the Save As button to create a new
unit system. Alternatively the Save button is disabled if none of the units selections
have been changed since the units system was last saved.
3.2.4 Using the Minimum and Maximum Limits
When you enter data in MBAL, the program checks that each input value is within a
range of values defined by a minimum and maximum value. This is to avoid wild values
being used as input to the calculations. Each measurement type has its own set of
limits.
MBAL provides a default set of limits but the units dialog allows you to edit these
values. Note that the minimum and maximum fields are displayed in the current
input units. If you edit these values the changes will remain in force until you exit the
program. However once you restart MBAL it will revert to the old limits.
If you wish to edit and then retain the validation limits, you can click the Save as
Default button after changing the minimum and maximum fields. This will mean that
any changes you make are used whenever you run MBAL.
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If you wish to return to the default limits that MBAL uses when first installed, delete the
file unit3.cfg in your windows directory.
3.2.5 Generating a Units Report
A report of the system units can be printed either directly to the printer, to an ASCII text
file, or the Windows clipboard. To print a units report choose the Report command.
You will be prompted to specify the output device and appropriate format. Click Report
again to start the report. When printing to a file, the program prompts you to enter a
name for the report. The .TXT extension is automatically given by the program.
3.3 Getting Help
If you are new to Windows, information about the help system can be found under the
HelpUsing Help option which can be accessed from the Windows desktop or MBAL
main menu. MBAL has an on-line help facility that allows you quick access to
information about a menu option, input field or function command without leaving the
MBAL screen. To use this facility, the help file must be located in the MBAL program
directory.
The help facility offers function buttons and jump terms to move around the Help
system. The function buttons are found at the top of the window and are useful in
finding general information about Windows help. If a feature is not available, the button
associated with that function is dimmed. Jump terms are words marked with a solid
underline that appear in green if you use a colour VDU. Clicking a jump term, moves
you directly to the topic associated with the underlined word(s).
3.3.1 Accessing Help
To get information quickly in MBAL, the following methods display the on-line help.
Help through the menu
From the menu bar, choose Help
Index or ALT H I, and select the subject you want
from the list of help topics provided.
Getting help using the mouse and keyboard
To get help through the mouse, Press SHIFT+F1. The mouse pointer changes to a
question mark. Next, choose the menu command or option to view. An alternative way
is to click the menu command or option to view, and holding the mouse button down,
press F1. To get help using the keyboard press the ALT key followed by the first letter
of the menu name or option and press F1.
Minimising Help
If you want to close the help Window, but not exit the help facility, click the minimise
button in the upper-right corner of the help window. If you prefer using the keyboard,
press ALT Spacebar N.
Petroleum Experts
Data Import
This chapter describes the MBAL program import facilities. These allow data to be
imported into MBAL from external files or databases.
4.1 Importing Data in MBAL
This facility enables you import tabular data from a wide variety of files and databases.
MBAL uses the idea of a filter ‘template’ for defining the format of a file or database to
be imported and how the data in the import file maps to the data in MBAL. These filters
can be configured visually and can be saved to disk for future use. They can also be
distributed easily to other users.
Wherever the
button is available, data can be imported directly into the
program tables. In some cases, the program provides the user with permanent (or
hard-coded filters) such as tubing performance curves imports or imports from the
binary files of other Petroleum Experts products. In most cases, user defined filters can
also be created and saved to disk. These software filters can be created and used
once (Temporary Filter), or they can be stored for future use (Static Filters).
Temporary filter:
A temporary filter is created by using the Temporary Filter file type. A temporary filter
can only be used once. After the data has been imported, the filter ‘script’ is destroyed
immediately afterwards.
Static filter:
If a filter is built as a Static Filter, the ‘script’ of the filter can be stored on the disk and
retrieved to be re-used or re-edited. It can also be distributed to other users of MBAL.
Static filter are stored in on disk into binary files with the MBQ extension.
Once the filter has been stored it will appear automatically in the File Type combo box.
To create a static filter, click on the Static Filter and then click on New (see the Static
Filter topic below).
The data import dialogue is used to import data from the 2 sources currently supported
by MBAL:
ASCII files
Open DataBase Connectivity sources (ODBC).
Depending on the type of data being imported, only some of the data sources may be
available.
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Figure 4.1:
Data import
Once a data source has been selected using the Import Type combo box, the dialog
will display only the fields relevant to that data source.
Command Buttons Data Import Dialogue
Done
Runs the selected filter and imports data into table
Static
Filter
Calls the static filter dialogue. If the current Import Type is ASCII file, an
ASCII file filters will be displayed. If it is ODBC, then an ODBC filter will be
created
ODBC Calls the ODBC administration program, which should reside in your
windows system directory if you have ODBC installed on your machine. The
program is used to set up data sources so that they may work with ODBC.
(ODBC option only)
The following two sections describe the method of importing data from the various data
sources.
4.1.1
Importing an ASCII File
This facility enables you import tabular data from a wide variety of files and databases.
You may select hard coded filters or build a static filter to import your data. A filter is
configured visually and can be distributed easily to other users. Each column of
numbers can be modified if the correct unit does no appear in the program. Once
configured the import static filters appear on the import dialogues together with any
hard coded import file types in the program.
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Figure 4.2:
Data import - ASCII files
Input Fields for ASCII file
File Name
The full path name of the file to import may be entered in this field. When you press
Done the file will be imported using the currently selected File Type. If a segment of a
path is entered into this field the dialog will be updated to show the contents of the new
directory.
File Type
This combo box displays the relevant import filters. These include the hard coded
filters and any static filters which have been created for this particular section of the
program (i.e. filters displayed when the import dialog is called from the PVT table will
be different to those shown when the import dialogue is called from the Production
History table. If the Temporary Filter option is left selected, the program will create a
temporary filter that is deleted once the data has been imported.
Browse
Click this button to select a file from your hard disk or network drive.
For more information on the set-up of the ASCII file import filter, see the ASCII File
Import section below.
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4.1.2
Importing data from an ODBC Datasource
This feature has been designed around the Open Data Base Connectivity standard to
present the user with a common interface to a wide variety of data sources. The
ODBC drivers which currently exist can support such diverse sources as dBase files
and Oracle 7. At present data can be imported from 1 table at a time and supported
with additional SQL to filter the data set.
ODBC is an addition to the operating system (i.e. Win95, NT 4.0) and as such is not
supplied by Petroleum Experts Ltd.
Figure 4.3:
Data import - ODBC Datasource
Input Fields for ODBC Database
Run Filter
This combo box shows the import filters which are relevant. The filters run by this tool
are similar to queries run on a database. If you have temporary filter selected a
temporary filter is created, but it deleted after the data has been imported. When a
filter, other than Temporary, has been selected you cannot select a data source from
the listbox.
Available Data Sources
This list box can be used to select any of the databases which have been set up with
ODBC tools on your computer. Once selected you can build a temporary filter to
import the data. This filter is destroyed after it has been run. To save a filter click the
static filter button to set up a permanent filter.
For more information on the set-up of the ODBC Database import filter see the ODBC
Database Import section below.
4.2 Static Import Filter
This feature allows you to build filters which can be re-used or even distributed to other
users of the program. Any filters that are built as static filters will be listed on the data
import dialogue. If it is an ASCII filter it will be in the list of filter types, and if it is for an
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ODBC data source it will appear in the list of filters to run. The temporary filter option
displayed in these lists is a static filter which is run once, then destroyed.
Static filters are administered with the Static Filter dialog shown below. This dialog will
list the filters for the current import type, i.e. if it is ASCII File only files which contain
ASCII filters will be listed. Consequently when the New, Copy or Edit buttons are
clicked you are given the options relevant to the import type.
Figure 4.4:
Static Filters
This screen is accessed by the Static Filter button on the file import dialogs which
appear throughout the program. It is from here that the import filters can be managed.
The list box is used to select a filter whose details are then displayed at the bottom of
the screen.
Command Buttons :
New
Creates a new filter then displays the Import Set-up screen.
Copy
Copies the currently selected filter then displays the File Import Filter
screen.
Edit
Reads the currently selected filter then displays the File Import Filter
screen
Delete Deletes the currently selected filter.
4.3 ASCII File Import
This facility is designed to let you import tabular data from a wide variety of files and
databases. A filter is configured visually and can be distributed easily to other users.
Each column of numbers can be modified if the correct unit does not appear in the
program. Once configured the import filters appear on the import dialogs together with
any hard coded import file types in the program. The following screens are only used to
modify these filters.
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4.3.1. Import Set-up
On this dialog you can specify the name and description of the filter to be created or
edited. It is also used to define the example file to be used when defining the filter.
Figure 4.5:
Import Set-up (ASCII file)
Input Fields
ASCII File
The full path name of the example file to be used for the definition of the filter must be
entered in this field.
File Format
Select the format of the example file specified above. This defines how MBAL
seperates the columns of data in the example file.
Name
A name for the filter type must be entered here. This will appear in the file type field of
an import dialog.
Description
Up to 120 characters may be entered here to give a more comprehensive reminder of
the operation of the filter. The description only appears in the bottom section of the
Details field on the Import Filters dialog.
Column Width
Enter the number of characters in which you wish each data column to be displayed in
the next filter definition dialog.
Command Buttons :
Browse
Calls up a file selection dialogue. The selected file and path is entered into
the ASCII file input field.
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Line Filter
On this screen the user can define the area of the file, which contains the data to
import. The check boxes may be used in together to build up complex rules. There is
a hierarchy to the rules to prevent duplication.
The First n lines and Last n lines options can be used to remove sections of the file
which are always of a fixed length. These two options define the area of the file within
which the rest of the options work.
The Before string and After string can be used to ignore parts of the file which may
vary in length. The string can be any pattern of characters which appear somewhere
on the boundary line.
The Table End section only has one option, Stop at First Blank line, which will cause
the import filter to stop reading data from the file at the first occurrence of a blank line.
All of the options above are processed in the order in which they are described.
Together they describe an area of the file in which the following options can remove
further lines from the data import.
The Lines starting with non numeric option will ignore all lines whose first character
(not including spaces) is non numeric.
The Lines starting with string option allows you to enter a pattern (up to .. characters)
which will then exclude lines from the import.
Figure 4.6:
Import Set-up (Line Filter)
Input Fields
All of these fields are only available if the option is checked.
First n lines
Enter the number of lines, starting from the top of the file, to be ignored.
Last n lines
Enter the number of lines, starting from the bottom of the file, to be ignored.
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Lines starting.
Enter the pattern which occurs at the start of lines to be ignored.
Before
Enter the pattern which occurs somewhere in the last line which is to be ignored (from
the start of the file).
After
Enter the pattern which occurs somewhere in the first line to be ignored (after reading
has started).
4.3.3
Import Filter
On this page you can define how the filter reads each line from the file. A text window
displays the ASCII file or database, which is completely greyed except for the data area
the first time this screen is displayed. From this screen data can be matched with the
variable names and the data units can be set.
If you are defining a new filter you should call up the Import Filter dialogue to define the
data area. Once this is done you may select columns of data for each field in the list
box. Once defined this column will be blue. If the selection in the Field Names list box
changes the column will turn red.
In the Field Format area you can set the units of the data in the import file. The Shift
and Multiplier fields can be used to modify the data before it is converted into the units
set for the program.
The graphical selections are echoed into the files in the Data Area section.
Alternatively the column number of line section may be entered here.
Figure 4.7:
Import Filter
Input Fields
Unit
A combo box can be used to list the units defined for the measurement in the MBAL
program.
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If the measurement is of time and the unit is date :
Format
A date format can be entered here using the characters Y, M & D separated by an “/”.
When no day is included in the date you are prompted for the day of the month on
which the measurements regularly occur. If the date in this field is to be the ‘end of the
month’ any number greater than 30 can be entered. If the data in the file contains no
delimiters the format defines the number of characters read as the day, month & year.
For example:
data:
data:
data:
data:
➲
MBAL
8901
8901
8901
89/01
format : YYMM
format : YYM
format : MYY
format : M/Y
result is January 1989
result in an error
results is August 1990
results is January 1989
picks up the default date format from the Windows International settings.
Otherwise:
Multiplier
Shift
The data read from the file is multiplied by this number.
This number is added to the product of the Multiplier and the data read
from the file.
If less than This field can be used to handle entries below this value in a special way.
If the carry over radio button is set, the last valid value read is copied to
this entry in the table. When the ignore radio button is set the value will
be set to a blank in the table.
If the file type is delimited :
Column
Enter the column of numbers displayed on the screen which contains the
data. Any valid graphical selection will be echoed in this field.
If the file type is fixed format :
Start Enter the column in which the data starts.
End
Enter the column in which the data ends.
These fields will echo any valid graphical selection and must contain the longest
number in the column of data.
Command Buttons:
Reset
Prompts the user to confirm the resetting of the data in the filter.
Filter
Displays the Import Filter dialogue.
Set-up Displays the Import Set-up dialogue.
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Done
When the user is defining a new filter a file selection dialogue is displayed
for you to enter a file name. If you are editing an existing filter it will be
saved automatically when this button is pressed.
4.4 ODBC Database Import
This facility is designed to let you import data from a database. The ODBC (Open
DataBase Connectivity) standard has been used as it allows the users to work in the
same manner with a wide variety of data sources. Note that you must have ODBC
drivers already installed on you PC to use these features. ODBC drivers are not part of
MBAL and must be purchased separately.
The ODBC filter operated in the same way as the ASCII filter (described above) with
the exception of the 2 dialogues used to define the data set.
4.4.1
Filter Set-up
This dialog is used to select the data source on which the filter is to be based. When
building a static filter you are required to enter a name for the filter which will appear in
the Run Filter combo box of the Data Import dialogue.
Figure 4.8:
Filter Set-up (ODBC)
Input Fields
Name
A name for the filter type can be entered here. This will appear in the file type
field of an import dialogue.
Description
Up to 120 characters may be entered here to give a more comprehensive
reminder of the operation of the filter. The description only appears in the
bottom section of the Details field on the Import Filters dialogue.
Available Data Sources
Data sources which have been configured to communicate with ODBC
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Command Buttons:
Done
Calls the Table/Fields dialogue
ODBC
Calls the ODBC administrator program.
4.4.2
Choose Table & Fields
Once a data source has been chosen you can select the table and fields to include in
your filter. Data can be imported from one table at a time with the current system.
Figure 4.9:
Import Filter
*
Input Fields
Tables
Select the table from which you want to retrieve data.
Fields
Select the fields that contain the data you want to import.
Additional SQL
Additional Structured Query Language can be entered here to filter the data set.
This section is designed for use with one shot filters ( i.e. Temporary;) and is not
saved in the static filter file.
Command Buttons:
Done Calls the Import filter dialogue, see section 4.3.3.
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Plots, Reports
This chapter describes the MBAL program plot and report facilities. It explains how to
modify a plot, change plot colours and print a plot display. This chapter also describes
the report dialogue box and explains how to set up a printer and prepare to print. The
commands described in this chapter are the MBAL Plot and Report commands, the File
-Printer setup and File - Plotter setup commands.
5.1 The Plot Screen
Plot screens can be accessed directly through the relevant dialogue box using the Plot
command button. Where data has been saved, the program also gives you the facility
of accessing a plot through the relevant menu. Throughout MBAL, the menu
command, or command button to access a graphic display will always be Plot. A
screen similar to the following appears:
Figure 5.1:
MBAL plot screen
Leaving the plot screen
The plot screen's Finish menu command will exit the current plot screen and return you
to the previous dialogue box.
5.1.1
Resizing the Display
A plot display can be enlarged to view a particular section of the display more closely.
This is done by zooming in on any portion of the screen. To magnify an area:
•
First place the plot cross-hairs near the area of interest. (Imagine drawing a box
over the area to view and position the cross-hairs on any corner of the box.)
•
Holding down the LEFT mouse button, drag the pointer diagonally across the
area of interest. A rectangle will temporarily be drawn over the area to magnify.
Release the mouse button.
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•
The screen display will automatically enlarge or magnify the area you have
selected.
•
After zooming, double-clicking the grid area or choosing the Redraw menu
command will reset the plot display to its original scales.
5.1.2
Modifying the Plot Display
Options are available in the Display menu to change the plot scales, axes labels and
plot colours. Displays can also be modified to exclude (or include) the plot legend,
cross-hair status information or curve data points.
➲
Any change made to a plot display applies only to the current active plot. That
is, changes to a plot display are plot specific.
Plot Scales
To change the plot display scales, choose Display - Scales. The following dialog box
appears:
Figure 5.2:
Plot Display - Scales option
•
Enter the new minimum and maximum values for the X and Y axis, and press
Done to return to the plot display.
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Plot Labels
To enter new labels for the plot title and axes, choose Display - Labels. The following
dialog box appears:
Figure 5.3:
Plot Display - Labels option
• Enter new labels for the plot title, X and Y axes, and press Done to return to the
plot display.
Plot Colours
The MBAL program uses a simple palette of colours that allows you to customise the
plot display to suit your personal preferences. You can customise the colour settings at
any time. The colours you choose can be saved so they become defaults for all plots,
and/or modified temporarily for a single plot. To access the plot colour options,
choose:Display
Colours. The following screen appears:
Figure 5.4:
Plot Display - Colours Option
The plot colour screen is generally sectioned into three parts : plot elements, plot
variables, and colour scheme. Every item in the lists displayed can be selected, and
each will accept any of the defined colours. To change a colour:• First select the desired colour scheme: colour, grey scale or monochrome; colour
schemes affect entire plots.
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• Next select the plot item to modify. To select a plot item, highlight the item name.
• Lastly choose the desired shade from the colour bar available for the scheme
selected.
• Separate colour schemes can be defined for the screen and hardcopy plots.
Plot Line Widths
This dialog allows you to change the width of lines on the plots. Enter a line width
between 1 and 9.
In most cases, the default value for the line width is acceptable for screens. However,
for printers with a very high resolution, the lines on the plots may appear too thin. In
these cases, try increasing the line width before selecting the hard copy option.
Once a change has been made to the line width, it will stay in force until exiting the
program. However, if you wish to keep the line width setting the next time you run the
program, click the Save button. This will store the line width setting in the INI file.
Plot Legends
The Display menu provides additional options for excluding (or including) the plot
legend, mouse status information and curve data points. To activate the appropriate
option click the menu item, or use the key combination indicated to the right of the
menu item. Where the option is active, a tick will appear to the left of the menu item.
• Legend Off, excludes the legend indicating the plot input data. (Shift+F6)
• Cursor Off, excludes the grey status bar located at the bottom of the plot screen
displaying the X and Y co-ordinates of the plot cross-hairs. (Shift+F7)
• Symbol Off, excludes the data points of the displayed plot curves. (Shift+F8)
5.1.3
Preparing to Plot
Once a plotter device has is chosen, and the appropriate set-up defined, making hard
copies of plots is straightforward. Before printing, verify the plotter device is plugged in,
on-line and connected to your machine. To define the plotter set up options choose
File - Plotter setup. The following screen will appear:
Selecting a Plotter
Figure 5.5:
Output Setup - Plotter selection
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•
On starting Mbal, the printer used is the default printer as specified by
Windows. However you can change to another printer within Mbal by clicking
on the Choose button. This will also allow you to select additional settings
appropriate to the printer.
•
Next select the preferred plot font and size. You are given the option of setting
the plot margins. Defaults are automatically provided by the program for the
plotter selected. These can be changed.
•
Select the preferred page orientation and colour scheme. Click Done to accept
the changes and exit the screen.
The set up dialog box that appears corresponds to the plot device selected. All devices
have varying plotting capabilities, but most devices allow you to select the paper size
and source, page orientation and number of copies.
5.1.4
Making a Hard Copy of the Plot
The Output menu command enables you to make or send copies of the plot display to
include in your reports. You are give the choice of selecting one on the following output
media :
•
Hardcopy, sends the plot display directly to the attached printer or plotter in the
format and layout specified in the Printer setup.
•
Clipboard, sends a copy to the Windows clipboard.
•
Windows Metafile, generates a *.WMF that can be imported into most Windows
The contents of the
clipboard are deleted and replaced whenever a new plot is sent to the
clipboard. If you want to keep the plot in the clipboard, start your preferred
Windows draw program and open a new document. Next, select the program's
Edit menu and choose the Paste command.
graphics programs (e.g. Freelance). A dialogue box appears promoting you
name the plot file. The extension is automatically given by the program.
All the above output options allow you to generate different types of colour plots:
-
Colour outputs the plot in the colours selected. This format is best if you have a
high quality colour laser printer/plotter.
-
Grey Scale outputs the plot is varying shades or grey.
displaying plots on LCD monitor or black and white screens.
This plot is useful for
-
Monochrome outputs the plot display is black and white only. This type is best
used with non-colour printers.
5.1.5
Changing the plotted variables
If you want to change the variables that are currently on the plot to display another set
of variables, choose the Variables menu command. The variable selection dialogue
box that appears will vary with the type of plot selected and the variable items that can
be displayed. To select a variable item, simply click the variable name, or use the ↑
and ↓ directional arrows and use the spacebar to select/de-select a variable item.
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5.2 The Report
This section describes how to select a printer and print or view a report, and describes
the report menu print options.
5.2.1. Preparing to Print
Once you have selected a printer and chosen the appropriate set-up options, printing
reports is simple. When you are ready to print, always verify your printer is plugged in,
on-line and connected to your machine. To define your printer set up options choose
File
Printer setup. The following screen will appear:
Selecting a printer
Figure 5.6:
Output Setup - Printer option
•
On starting Mbal, the printer used is the default printer as specified by
Windows. However you can change to another printer within Mbal by clicking
on the Choose button. This will also allow you to select additional settings
appropriate to the printer.
•
Next select the preferred plot font and size. You are given the option of setting
the plot margins. Defaults are automatically provided by the program for the
plotter selected. These can be changed.
•
Select the preferred page orientation and colour scheme. Click Done to accept
the changes and exit the screen.
The set up dialog box that appears corresponds to the plot device selected. All devices
have varying plotting capabilities, but most devices allow you to select the paper size
and source, page orientation and number of copies.
5.2.2
Printing a Report
As a safeguard, we recommend you save your data file prior to printing a report. In the
unlikely event of a printer error or some other unforeseen problem, this simple
procedure could prevent any work from being lost. Report options are provided in all
the relevant dialogue boxes and/or menus.
When choosing the Report command from a menu, the program prompts you to select
the categories of data to print and the appropriate report settings. When choosing the
Report command button, the program will prompt you for the report settings only as it
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knows the data it is to print. On choosing the Report command, a dialogue box similar
to the following appears:
Figure 5.7:
MBAL Report selection
•
Select the categories of data to print from the Sections to Report list. Selected
categories are retained in memory and printed each time a report is generated.
Categories between brackets, (e.g.<PVT>) indicate further report categories
can be selected. To access these categories, click the small arrow button to
the right of the report name.
•
Select the output device:
- Printer, sends the results directly to the attached printer in the format and
layout specified in the Printer setup.
-
File, generates and ASCII text file (*.TXT) that can be imported into any
word processing or spreadsheet program (e.g. Windows Write, MS Excel).
A dialogue box appears promoting you name the report. The extension is
automatically given by the program.
-
Clipboard, sends a copy to the Windows clipboard, where you can view or
copy the data into any word processing or spreadsheet program. The
contents of the clipboard deleted and replaced whenever new data is
copied to the clipboard. If you want to copy a report from the clipboard,
start your preferred Windows word processing or spreadsheet program and
open a new document. Next, select the program's Edit menu and choose
the Paste command.
•
Display, displays a window where you can view the report.
Next select the report format: (available for File and Clipboard options only)
-
A fixed format report delimits the data columns with blank spaces. This
format is fine for viewing data.
-
A comma delimited report spaces the data columns with commas.
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-
5.2.3
A tab delimited report spaces the data columns with tabulation markers
which allows you to easily create tables or format data. Use this format
when exporting reports to word processing or spreadsheet programs.
Viewing a Report
The alternative to printing a report is viewing it, particularly if the data is only temporary
or an intermediate step in the analysis. To view a report, choose the Report command
in the relevant dialogue box, and select Clipboard as the output device. Next choose
File
Clipboard to display the 'Clipboard Viewer' and the contents of the report.
5.2.4
Solving Printing Problems
If your printed output does not look like the format you see on screen, check the
following:
• Make sure you have sufficient space on disk to create a printer file.
•
Check your printer is connected properly, it is ON and on-line.
•
Check you have selected the correct printer and port from the Printer Set Up.
If can't read the printer file, check the appropriate printer port is selected
(usually 'LPT1').
•
Check you have installed the correct fonts and printer fonts for your driver.
When Windows cannot find the appropriate fonts, it substitutes another font.
•
Check that the latest version of your printer driver has been installed. If you
have an old printer driver, the document may not print or will compress to form
an unreadable file.
Petroleum Experts
Defining the system
The following sections describe the parameters that define the reservoir conditions and
intended analytical use of the MBAL program. This chapter describes the program Tool
and Options menus.
The selections you make in these screens set the scope of the MBAL program. They
establish the kind of input you will be required to enter and specify the nature of the
calculations you will perform. The parameters you select are global for the current
active file.
On selecting the analysis tool, you may immediately notice the options on the menu bar
change. This is the effect of MBAL's smart data input feature. The menu bar changes
when you select a different tool. The options displayed will correspond to the analysis
tool selected and are different between tools. This smart menu feature simplifies the
process of data entry by displaying only those options, fields and input parameters that
are relevant to your application.
You can change your selections at any time. You must remember however, that new
choices may require more or different data to be supplied and in some cases
recalculated.
6.1 Reservoir Analysis Tools
The function of the Tool menu is to define the reservoir engineering analysis tool. The
menu lists the current Reservoir Engineering tools available in MBAL.
To access this menu, click the menu name or press ALT T. The following analytical
tools are displayed:
• Material Balance
Uses Water Influx models for Linear, Bottom Drive or Radial flow. Relative
permeabilities and well performances are used (IPR, VLP) to predict future reservoir
performances.
•
Monte Carlo Statistical Modelling
Statistical tool for estimating Oil and Gas in place.
•
Decline Curve Analysis
Hyperbolic analysis of single well production.
•
1D Model
Analysis of gas or water flooding in an oil reservoir.
•
Multi Layer
Calculation of pseudo-relative permeabilities for a multi-layer reservoir.
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6.2. System Options
Once the analysis tool has been selected, go to the Options menu to establish the
primary fluid of the reservoir. This dialogue box has three main sections:•
Tool Options
Specify the different options available for the tool selected in the Tool menu.
•
User Information
Enter some general heading information. These fields identify the reservoir
and appear on the report and screen plots.
•
User Comments
Space where you can keep a log of the updates/changes to the file. It can also
be used to exchange information between users.
To access the Options menu, click the menu name or press ALT O. A dialogue similar
to the following appears:
Figure 6.1:
MBAL- System Options
Tool Options
To select an option, click the arrow to the right of the field to display the current
choices. To move to the next entry field, click the field to highlight the entry, or use the
TAB button. The options displayed are determined by the analysis tool selected in the
Tool menu. For more information on these fields, refer to the relevant analysis tool
chapter.
User information
The information for these fields is optional. The details entered here provide the
banner/header header information that identify the reservoir in the reports and plots
generated by the program.
User comments and Date stamp
This box is used to keep a history log of events on the system or modifications made to
the file since you started. An unlimited amount of text is allowed. Press Ctrl+Enter to
start a new paragraph.. The comments window can be viewed by either dragging the
scroll bar thumb or using the ↑ and ↓ directional arrow keys. The Date Stamp
command adds the current date and time to the user comments box.
Petroleum Experts
Describing the PVT
In order to accurately predict both pressure and saturation changes throughout the
reservoir, it is important that you accurately describe the properties of the fluid. In an
optimum situation, this data is determined from laboratory studies of fluids and core
samples. As this is not always possible, MBAL offers several options for calculating the
required fluid properties:
- Correlations : Where only basic PVT data is available, the program uses traditional
black oil correlations.
- Matching : Where both basic fluid data and some PVT laboratory measurements are
available, the program can modify the black oil correlations to best-fit the measured
data using a non-linear regression technique.
- Tables : Where detailed PVT laboratory data is provided, MBAL uses this data instead
of the calculated properties. This data is entered in table format (PVT tables), and can
be supplied either manually or imported from an outside source. So called black oil
tables can be generated from an EOS model and then be imported and used in Mbal.
7.1 Entering the PVT
The following paragraphs summarise the steps to take based on the amount of PVT
information you have available.
Using PVT correlations
•
Choose PVT - Fluid Properties, and enter the data requested in the input dialog
box. Select the correlation known to best fit the fluid.
Where additional PVT laboratory data is available:
Using PVT matching
•
Choose the Match command to enter the PVT laboratory data. The measured
data and fluid data entered in the 'Fluid Properties' screen must be consistent.
Flash Data must be used. Up to 5 input tables for different temperatures are
allowed. The bubble point should be entered in the match table for each
temperature as well.
•
Choose the Match command to adjust the selected correlation with the PVT
measured data. Check the parameters and correlations to match. Choose
Calc to start the non-linear regression that will modify the correlations. Click
Results to view the matching parameters. Identify the correlation with the
lowest correction (parameter 1) and standard deviation, and use this correlation
in all further calculations of fluid property data.
Chapter 7 - Describing the PVT
7-2
Section II
Using PVT tables
•
Choose PVT
Fluid Properties, and enter the data required in the input dialog
box. Select the correlation known to best fit the fluid type.
•
Choose the Tables command to use the PVT tables. Up to 5 input tables for
different temperatures are allowed. Enter the data manually, or choose the
Import command to import the PVT data from an external source. Ensure the
'Use Tables' option is checked in the PVT data input dialog.
Checking the PVT calculations
•
To determine the quality of the PVT calculations, return to the 'Fluid Properties'
dialog box and click Calc. Enter a range of pressures and temperatures for the
calculation.
The ranges defined should cover the range of pressures
expected.. The calculations performed can be:
- Automatic, where fluid properties are calculated for a specific range and
number of steps, or
- User defined, where fluid property values are calculated for specific
pressure and temperature points.
Choose Calc to return to the calculation screen. The previous calculation results are
displayed. Choose Calc again to start a new calculation.
When the calculations have finished click Plot to view the calculated and measured
results.
7.1.1
PVT Setup
This dialog is used to setup various attributes relating to the PVT input and models.
Water Viscosity Pressure Correction
At V6.0 of MBAL, we added a correction to the water viscosity as a function of
pressure. Tick this option if you wish to use this correction. If you wish to use the same
water viscosity calculation as was used in V5.0 and before, leave the box unticked.
Note that the correction (if selected) will be used in all the PVT models for this
particular data file.
7.1.2
PVT for Oil
If Oil is defined as the fluid type in the Options menu, the following PVT dialog box is
displayed.
Petroleum Experts
Chapter 7 - Describing the PVT 7-3
Figure 7.1:
PVT for Oil : Data input
•
➲
Enter the required fluid data in the fields provided.
- The Formation GOR is the Solution GOR at the bubble point and should not
include free gas production.
- The Mole Percent, CO2, N2 and H2S are from gas stream composition.
•
•
•
•
Select the appropriate Separator (Single or Two Stage)
Select the black oil correlations to apply.
If PVT Tables have been entered, and you decide to use the matched or
unmatched black oil correlations instead of the tables, un-check the Use Tables
box. Refer to section 7.3 for more information.
If the black-oil correlations have been matched, and you decide to use the
original (unmatched) black oil correlations instead, un-check the Use Matching
box. Refer to section 7.2 for more information.
Where additional PVT data can be provided, continue with the 'Matching Correlations...'
and 'Using the PVT Tables' sections. If no further data is available, click Done to exit the
PVT menu.
7.1.2.1 Controlled Miscibility
This option is used to control how free gas redissolves into the oil if the pressure of the
fluid increases.
Firstly it is worth reviewing how gas re-dissolving was handled in older versions of Mbal
(and how it is still handled if this option is not selected).
Consider a fluid that starts above the initial bubble point. As the pressure drops, the oil
is still undersaturated so no gas bubbles out of the oil. If the fluid continues to drop to
below the initial bubble point, gas will start to bubble out of the oil. The amount of gas is
described by the saturated part of the Rs vs Pressure curve as defined by the PVT
model.
Now if the pressure of the fluid starts to increase, Mbal simply backtracks up the Rs vs
Pressure curve. In other words, we assume that the gas re-dissolves back into the oil at
exactly the same rate as it bubbled out. If the presure increases further, back above the
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initial bubble point pressure, Mbal still keeps to the original Rs vs Pressure curve.
Therefore the amount of gas that can be re-dissolved back into the oil is limited to the
initial Rs. So even if we have injected gas into the sample, it can still not be dissolved
into the oil above the initial Rs - no matter how high the pressure reaches.
So what are the changes if the controlled miscibility option is selected? In fact, as the
pressure drops from the initial pressure, there is no change in the PVT model from
before. The Rs will stay constant until the tank drops below the initial bubble point
pressure - it will then decrease as specified by the saturated Rs vs P curve. It is only if
the pressure starts to increase that we see a change. Firstly, Mbal can now limit the
amount of gas that can redissolve into the oil - this is specified by the gas remixing
value (x) entered in the PVT dialog. Mbal will keep track of the lowest value of Rsref
during a prediction/simulation etc and use this as a reference point.
At each calculation step, Mbal does the following. It first calculates the maximum
amount of gas that can be dissolved in the oil if limitless gas is available and the gas
has infinite time to dissolve. It then calculates the maximum Rs available in the system
i.e. the available gas to available oil ratio. It then sets the potential Rs (RsPot) to the
minimum of these two values i.e. we are either limited by the available gas or the
maximum gas that can dissolve. We then calculate the actual Rs to be:Rs = (1 − x) RsLast + xRsPot
RsLast is the Rs at the last time step. x is adjusted to be the remixing given the length
of the time step. x is limited to a maximum of 1.0. If you wish all the gas to be
redissolved at each time step, then simply enter a very large number for the remixing
e.g. 1.0e08. A value of 0.0 will mean that no remixing will occur.
Note that each time we calculate a new Rs, we also recalculate the corresponding new
bubble point.
Secondly, if the pressure rises above the initial pressure, Mbal will allow the Rs to rise
above the initial Rs, assuming that the remixing factor is large enough, enough gas is
available from injection and the oil can dissolve more gas. Note that if the pressure
keeps rising, but the available gas runs out so the oil becomes undersaturated again,
Mbal will use fluid properties based on undersaturated properties calculated from the
new bubble point.
7.1.3
PVT for Gas
When Gas is defined as the fluid type in the Options menu, the following PVT dialog
box is displayed.
➲
The program assumes all liquid dropout occurs at the separator. In the
calculations, an equivalent gas rate is used that allows for condensate and water
production to ensure that a mass balance is observed.
Petroleum Experts
Chapter 7 - Describing the PVT 7-5
Figure7 7.2
PVT for Gas : Data Input
•
Enter the required fluid data in the fields provided.
➲
- The Mole Percent, CO2, N2 and H2S are from gas stream composition.
•
•
Enter the required separator data in the fields provided.
Select the Gas Viscosity correlation to apply.
Where additional PVT data can be provided, continue with the 'Matching Correlations...'
and 'Using the PVT Tables' sections. If no further data is available, click Done to exit the
PVT menu.
7.1.4
PVT for Retrograde Condensate
If Retrograde Condensate is defined as the fluid type in the Options menu, the
following PVT dialog box is displayed.
Figure 7.3:
PVT Retrograde Condensate :
Input
•
➲
•
Enter the required fluid data in the fields provided.
- If Tank GOR and Tank Gas Gravity are unknown, they may be left at 0.
If this is the case, the total produced GOR should be entered under Separator
GOR.
- Condensate gravity is at standard conditions.
Select the Gas Viscosity correlation to apply.
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Where additional PVT data can be provided, continue with the 'Matching Correlations...'
and 'Using the PVT Tables' sections. If no further data is available, click Done to exit the
PVT menu.
7.1.5
Variable PVT for Oil Reservoir
In an attempt to take into account the change of black oil properties versus depth, a
‘Variable PVT’ tank model has been implemented. To enable this tank model, select
‘Variable PVT’ as the tank model in the Options menu.
In this model, the tank is divided into several ‘layers’ having different PVT properties.
Describe the average PVT properties of each layer. If measured data is available, do
not forget to match each layer PVT correlations by clicking on the Match Data button.
(see 'Matching Correlations’ below). Note that a '*' will appear on the Match Data button
if the match process has already been performed on a layer.
The depths entered here must match the depths entered in the reservoir pore volume
versus depth table(see Tank Input). If a primary gas cap exist, the Datum Depth must
be the depth of the initial Gas/Oil contact. The Datum Depth must correspond to the 0
pore volume versus depth and the bottom depth of the last layer must correspond to
the 1 pore volume versus depth.
➲
The datum depth defines the top of the top layer, so all layer bottom depths must
be greater than the datum depth. Mbal will sort the layers in the table by the
layer bottom depth. Mbal will also stop you entering layers less than one foot
thick.
The following PVT dialogue box is displayed.
Figure 7.4:
Variable PVT: Input
•
Enter the required fluid data in the fields provided.
Petroleum Experts
Chapter 7 - Describing the PVT 7-7
➲
- The Formation GOR is the Solution GOR at the bubble point and should not
include free gas production.
- The Mole Percent, CO2, N2 and H2S are from gas stream composition.
Click Done to exit the PVT menu.
7.1.6 PVT for General Model
If the General fluid model has been selected in Options menu, a tabbed dialog is
displayed. There are three tabs:-
-
-
Oil : This tab will display the same fields as on the standard oil or variable PVT
dialog. The only difference is that the water inputs and the gas impurities are
not displayed.
Gas : This tab will display the same fields as on the standard retrograde
condensate dialog. The only difference is that the water inputs are not
displayed.
Water : This tab displays the water inputs that normally appear on the oil or
retrograde condensate.
In this case, the oil properties are calculated from the model entered in the oil tab, the
gas properties are calculated from the model entered in the gas tab and the water
properties are calculated from the model entered in the water tab.
The Import, Match, Table and Match Param buttons on each tab will operate on each
phase model separately. For example, each phase can be matched separately.
However the results calculated from the Calc button will always be from the
combination of the three models.
It is also possible to exclude use of the full model for either the oil or gas phase. This
allows compatibility with old oil or retrograde condensate models. For example, if you
do not have a full model for the gas phase, you may switch the Use Full Gas Model
option off. In this case, the gas properties will be calculated from the oil model i.e. the
same as the standard oil model. Note that the water properties will still be calculated
from the data in the water tab.
7.1.7 Multiple PVT Definitions
In some circumstances, the PVT section will allow you to define more than one set of
PVT data. Note that each set of PVT data includes the input PVT (e.g. GOR, API, gas
gravity) as well as matching tables, matching parameters and table data. In these
cases the above dialogs will look slightly different:• All the currently defined sets of PVT data will be listed down the right hand side
of the dialog. Click on the PVT definition you wish to edit – all the fields and the
actions relating to the buttons will now act on the PVT definition selected.
• An extra field will be displayed at the top of the dialog to allow you to change
the name of the PVT definition.
• Three buttons are also displayed at the top of the dialog. Click on the plus
button to create a new empty PVT definition. Click on the minus button to
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Section II
delete the currently selected PVT definition. Click on the the multiply button to
create a new PVT definition which is a copy of the currently selected PVT
definition.
7.2. Matching correlations
The matching facility is used to adjust the empirical fluid property correlations to fit
measured PVT laboratory data. Correlations are modified using a non-linear regression
technique to best fit the measured data. You access this facility by clicking the Match
command in the 'Fluid Properties' dialogue box. A similar screen to the following
appears:
Figure 7.5:
PVT Match : Data Input
Up to 5 PVT tables can be entered. Tables are sorted by temperature.
•
➲
Enter a value for the input field(s).
Flash Data not differential liberation data should be used for matching.
•
Enter the corresponding measured PVT laboratory data in the columns
provided. To select the next PVT table, check the next free radio button.
➲
- When matching condensate density, there should be no input pressure higher
than Dew
Point, as the condensate density does not exist beyond that point.
•
Once you have entered all your data, click Match to select the fluid properties
and correlations to match.
Petroleum Experts
Chapter 7 - Describing the PVT 7-9
Figure 7.6:
Matching measured PVT to
the correlations
Match On
Individual fluid properties, or combination of properties can be
matched against the correlations. Dimmed entries indicate no
measured data has been entered. Clicking All/None will select or
deselect all the properties to match. To select properties, check the
appropriate box.
Correlations You can match all or selected correlations to the fluid property data.
Checking the Match All box will flag all the correlations for matching.
•
Select the properties and correlations to modify with the measured PVT data.
•
Click Calc to start the match process. The regression technique applies a
multiplier (Parameter 1), and a shift (Parameter 2) to the correlation. The
Standard Deviation displays the overall match quality. The lower the standard
deviation, the better the match.
When the calculations are done, the match coefficients for the selected correlations
and fluid properties are displayed under Match Statistics. The coefficients for each
property can be viewed by selecting one of the correlations. To view or change
coefficients for all, click Match Param.
➲
To unmatch correlations, click Reset. All matching parameters will be reset to 1
and 0 respectively.
Note that the form of the oil FVF correlation is different above and below the bubble
point. To avoid problems when matching, always enter data at the bubble point.
Separate correlation match parameters are available for matching FVF above the
bubble point. For undersaturated reservoirs, it is essential that the FVF is correct - the
slope of the FVF at a particular reservoir pressure yields the oil compressibility. History
match accuracy for undersaturated reservoirs is critically dependent on the accuracy of
the oil FVF correlation.
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Figure 7.7:
Match Data results
7.3 Using PVT tables
If detailed PVT laboratory data is available it can be entered in the tables provided. The
program will use the data in the PVT tables in all further calculations only if the 'Use
Tables' option in the 'Fluid Properties' data entry screen is enabled.
Up to 5 PVT tables can be entered, and each table may use a different temperature if
desired. Tables are sorted by temperature. Where the program requires data that is
not entered in the tables it will calculate it using the selected correlations. To access
the PVT tables:
•
Enter the information required in the input dialogue box. Select the correlation
known to best fit the fluid type. Check the 'Use Tables' option in the data input
screen, and click Tables. A 'User Table' dialogue box similar to the following will
appear.
Petroleum Experts
Chapter 7 - Describing the PVT 7-11
Figure 7.8:
PVT Tables Input dialogue
•
Enter the measured PVT data in the columns provided. To select the next PVT
table, check the next free radio button.
The Import facility is an alternative method of entering data. The option is open to any
user who would like to use data from their own programs. As file formats vary across
programs, this option is user specific. The general file import facility is described in
Chapter 4, Section 3.
➲
For the material balance tool, if a fixed value for water compressibility has been
entered in the tank data, it will ignore any values entered for Bw in the PVT
tables.
If no further data is available, click Done to exit the PVT menu.
7.3.1
PVT Tables for Controlled Miscibility
If controlled miscibility has been selected, the table entry has some differences. As
before, one can enter up to 5 tables with a different temperature for each set. However
for each temperature one must enter a single saturated table and up to 5
undersaturated tables. Each undersaturated table corresponds to different bubble
point.
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7.4. Checking the PVT calculations
To check the quality of the PVT data entered, click Calc in the 'Fluid Properties' screen
or choose PVT
Calculator. A dialogue box similar to the following appears:
Figure 7.9:
Oil Automatic Calculation
•
Select the correlations to apply. These default from the Fluid Properties input
screen, and can be changed to test the other correlations.
•
Check the method of calculation (Automatic or User Selected)
Automatic
Enter a range of pressures and temperatures, and the number of
steps to calculate for each.
User selected A separate input screen appears that allows you to enter up to 10
specific pressure and temperature points to check.
•
•
If the controlled miscibility option has been selected then the bubble point is not
fixed. So you will also need to enter the bubble point Pb at which you wish the
calculations to be done.
Click Calc. A calculation screen showing the results of the previous calculation
appears.
Petroleum Experts
Chapter 7 - Describing the PVT 7-13
Figure 7.10:
PVT Calculation screen
•
Click Calc again to start the calculation.
•
To view the calculation results graphically, click Plot. A graphics screen similar
to the following appears:
Figure 7.11:
PVT Plot screen.
You can view other PVT variables by choosing the Variables menu option. The
program allows you to modify much of the plot display. You can change the plot
colours, labels and scales or the variables displayed on the X and Y axes. To change a
plot display, use any of the following menu options on the menu bar.
Finish
Closes the plot.
Redraw
Cancels any zoom and redraws the original plot.
Display
Use this option to access the facilities for changing the plot scales,
plot labels and plot colours.
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Output
Use this option to make a copy of the plot display. The plot can be
sent directly to 'the printer, the Windows clipboard or into a
Windows Metafile.
Variables
Use this option to select different display variables for the X and Y
axes.
Next Variable
Use this option to select the next PVT variable to plot.
Versus
Set the x-axis i.e. pressure or temperature.
Help
Display the appropriate help topic.
7.4.1
PVT Command Buttons
Calc
Displays a calculation screen where the calculations on the input
parameters for the selected correlations are performed.
Import This option is used with the Tables command, and is open to users who
would like to bring in their PVT data from an outside source. This option
is user specific an the general import facility is described in Chapter 4,
Section 3.
Match
Displays a variable entry screen where you can enter measured PVT
laboratory data to modify the available correlations to fit the measured
data.
Plot
Displays a graphics screen where calculated results are visually
displayed.
- To select other axis variables, choose the 'Variables' command.
- To change the plot scales, labels or colours, choose the 'Display'
command.
- To generate copies of a selected screen plot, choose the 'Output'
command.
Match Displays a variable entry screen where you can view or edit the current
Param calculated match parameters.
Reset
Used in the Match Data calculation screen, the Reset command reinstates
the matched correlations to the original text book correlations.
Table
Displays a variable entry screen where you can enter or import detailed
PVT laboratory data. This command works with the 'Use Tables' flag.
When the option is checked, the program uses the measured data in the
PVT tables. If the program requires data that is not provided in the tables,
it will calculate the data using the selected correlation.
Petroleum Experts
Chapter 7 - Describing the PVT 7-15
7.5 Fluid Compositions
This section describes how to enter/edit/view a fluid composition, plot its phase
envelope and generate fluid properties.
It is not possible to use a composition to replace the black oil models described earlier
in this chapter. The only use for fluid compositions is for compositional tracking in the
material balance tool. The use of the compositions is therefore described in the
Material Balance – chapter 8.
7.5.1 Entering the Components
When the Oil, Gas or the Gas Injection Composition menu item is selected, the main
composition dialog is displayed.
Figure 7.12:
PVT Main Composition screen
This dialog is used to enter/edit/view a fluid composition. This main dialog allows you to
enter the number of components as well as their names. One can then enter the
various properties per component. It also allows selection of the volume shift option.
There are additional dialogs which can be accessed from this screen to enter Binary
Coefficients and the Separator Conditions.
The description of the composition will be displayed in the window title.
For a dataset, the number of components and the component names must be identical
for all the input compositions. If you want to effectively exclude a component in a
particular composition then enter a very small fraction (i.e. 1.0e-06) - note that it is not
valid to enter a fraction of 0.0.
If the composition is for display only, it will not be possible to type anything into the
cells.
7.5.1.1 Accentric Factors
The accentric factor was put forward as a means of representing the non-sphericity
and polarity of many compounds. The original Equation of State PV=nRT was based
on a model of hard spheres which behaved in a classical and predictable fashion. The
vast majority of compounds are, unfortunately, far from ideal and far from spherical.
The accentric factor provides a number which can be used in the equation of state to
match predicted PVT behaviour with reality.
The accentric factor enters the equation as a component which describes the change
in the intermolecular attraction component a with temperature.
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The table below shows some typical accentric factors. Note that the value increases
with the size of the molecule and its polarity.
Common Accentric Factors:Compound
Nitrogen N2
Carbon Dioxide CO2
Methane C1
Ethane C2
Butane nC4
Hexane C6
Octane C8
Decane C10
Accentric Factor
0.039
0.239
0.011
0.099
0.199
0.299
0.398
0.489
It is particularly important to select the right accentric factor for pseudo components.
7.5.1.2 Composition Command Buttons
BI Coeffs
Displays a screen where the binary coefficients of the fluid composition
can be entered.
Phase Env This option is used to calculate and plot the phase envelope for the
current composition.
Import
This option is used to import a fluid composition from a PRP file. This
file type can be exported by the Petroleum Experts PVT program.
Export
This option is used to export the current fluid composition to a PRP file.
Seperator Displays a screen where you can enter/edit/view the seperator
conditions for the fluid composition.
Reset
This option can be used to delete the current composition.
Generate This option is used to generate a table of fluid properties for the current
fluid composition using the Peng-Robinson equation of state. A range
of temperatures and pressures may be entered and the properties
calculated for each combination of temperature and pressure.
Petroleum Experts
Chapter 7 - Describing the PVT 7-17
7.5.2 Binary Coefficients
When the BI coeffs button on the main composition screen is clicked, the following
screen is displayed to allow entry or viewing of the binary coefficients.
Figure 7.13:
PVT Binary Coefficients screen
The cubic equations of state were originally developed for pure substances. With time
their use was extended to mixtures. This extension required some method of
introducing a measure of the polar and other interactions between pairs of dissimilar
molecules. The binary interaction coefficient was put forward.
This variable enters the calculation as a component in the intermolecular attraction a.
a=∑
For mixtures:i
∑z z a
i
j
ij
j
where zi and zj are mole fractions of components i and j, respectively and :
aij = (aa) 0.5 (1 − k ij )
kij is the binary interaction coefficient.
Binary Interaction Coefficients represent a flexible way of moulding the ideal Equation
of State to match the non-ideal reality of many mixtures.
Use this screen to enter the binary interaction coefficients associated with the pseudo
composition entered on the previous screen. As this table is symmetrical about the
diagonal only half the table has to entered. The program will automatically duplicate the
other half. No values need be entered on the diagonal.
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7.5.3 Separator Conditions
When the Separator button on the main composition screen is clicked, the following
screen is displayed to allow entry or viewing of the separator conditions.
Figure 7.14:
PVT Saparator Conditions screen
Up to five sets of separator conditions can be entered.
7.5.4 Phase Envelope
This feature displays a graphical representation of the phase envelope at 100 percent
vapour fraction. The program will determine and display whether it is a Dew Point or a
Bubble Point system and automatically calculate the cricondentherm, cricondenbar and
where applicable, the critical point.
When the Phase Env button on the main composition screen is clicked, the following
screen is displayed.
Figure 7.15:
PVT Phase Envelope Calculation
screen
First click the Calculate button. This will calculate and display the phase envelope as
well as the fluid system, Critical Point, Cricondentherm and Cricondenbar. Then click
the Plot button to display the plot of the phase envelope.
Petroleum Experts
Chapter 7 - Describing the PVT 7-19
7.5.5 Fluid Properties Calculations
This features allows calculation of the fluid properties of a composition over a range of
temperatures and pressures.
When the Generate button on the main composition screen is clicked, the following
screen is displayed to allow entry of the ranges of pressure and temperature over
which to calculate.
Figure 7.15:
PVT Composition Calculation
Range screen
Up to five sets of separator conditions can be entered.
Enter the lowest temperature required in the From field and the highest in the To field.
Then enter the number of points required. Note that if only one temperature is required
then enter the same value in the From and To field (as shown in the screen above).
Repeat for the pressure.
Then click on the Calculate button to calculate and view the results. This displays the
following screen.
Figure 7.167:
PVT Composition Calculation
screen
Now click on the Calculate button to calculate and view the results.
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Material Balance Program Version 6
The Material Balance Tool
The Material Balance method is by no means a universal tool for estimating reserves. In
some cases it is excellent. In others it may be grossly misleading. It is always instructive
to try it, if only to find out that it does not work, and why. It should be a part of the 'stock
in trade' of all reservoir engineers. It will boomerang if applied blindly as a mystic hocuspocus to evade the admission of ignorance. The algebraic symbolism may impress the
'old timer' and help convince a Corporation Commission, but it will not fool the reservoir.
Reservoirs pay little heed to either wishful thinking or libellous misinterpretation.
Reservoirs always do what they 'ought' to do. They continually unfold a past with an
inevitability that defies all 'man-made' laws. To predict this past while it is still the future is
the business of the reservoir engineer. But whether the engineer is clever or stupid,
honest or dishonest, right or wrong, the reservoir is always 'right'.1
Overview:
The material balance is based on the principle of the conservation of mass:
Mass of fluids originally in place = Fluids produced + Remaining fluids in place.
The material balance program uses a conceptual model of the reservoir to predict the
reservoir behaviour based on the effects of reservoir fluids production and gas to water
injection.
The material balance equation is zero-dimensional, meaning that it is based on a tank
model and does not take into account the geometry of the reservoir, the drainage areas,
the position and orientation of the wells, etc.
However, the material balance approach can be a very useful tool to:
-
Quantify different parameters of a reservoir such as hydrocarbon in place, gas cap
size, etc.
-
Determine the presence, the type and size of an aquifer, encroachment angle, etc.
-
Estimate the depth of the Gas/Oil, Water/Oil, Gas/Water contacts.
-
Predict the reservoir pressure for a given production and/or injection schedule,
-
Predict the reservoir performance and manifold back pressures for a given
production schedule.
-
Predict the reservoir performance and well production for a given manifold pressure
schedule.
1Quotation by Muskat, taken from an excerpt in the 'Reservoir Engineering News Letter', September 1974.
Chapter 8 - The Material Balance Tool
Section III
8-2
Material Balance Tank Model Assumptions :
The Material Balance calculations are based on a tank model as pictured below:Figure 8.1:
Material Balance Tool Tank Model Assumptions
Throughout the reservoir the following assumptions apply:• Homogeneous pore volume, gas cap and aquifers,
• Constant temperature,
• Uniform pressure distribution,
• Uniform hydrocarbon saturation distribution,
• Gas injection in the gas cap,
• Gas injected remains in gas phase.
The Material Balance Program can handle:
•
•
•
•
Oil, gas or condensate reservoirs,
Linear, radial and bottom drive reservoir and aquifer systems,
Naturally flowing, gas lifted, ESP, gas or water injector wells,
In predictive mode, automatic shut-in of well based on production or injection
constraints,
• The use of tubing performance curves to predict well production,
• The use of relative permeability tables or curves.
• Multiple tanks with transmissibilities between them.
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• Single oil tanks with variable PVT vs. Depth.
The Material Balance Tool is divided into three main sections:
1. The INPUT section, where the following information can be entered:
- Known and estimated reservoir parameters,
- Known or estimated aquifer type and properties,
- Pore volume fraction versus depth (optional),
- Relative permeability curves,
- Transmissibility parameters (optional),
- Production and injection history on a well to well basis or total tank production.
2. The HISTORY MATCHING section, where:
- A graphical method (P/Z, Havlena Odeh, ...) is used to quantify the missing
reservoir and aquifer properties.
- An iterative non linear regression is used to automatically find the best
mathematical fit for a given model.
- A simulation of production can be run to check the validity of the results of the
above two techniques.
- Gas, oil and water relative permeabilities can be estimated from historical GOR,
WCT or WGR.
3. The PRODUCTION PREDICTION section,
where reservoir performances can be simulated assuming:
- production and constraint schedules,
- gas contracts,
- relative permeabilities,
- well performance definitions,
- a well schedule or drilling program.
Note:
− It isn't necessary to enter the reservoir production history to run a Production
Prediction.
− It is highly recommended to tune the reservoir & aquifer models if any production
history data is available.
− If you do not wish -or do not have data- to tune the models, the 'Production History'
section of the Input menu, and History Matching menu can be completely
ignored.
− You will still have to enter the Reservoir Parameters & Aquifer Parameters sections
of the Input menu.
− Relative permeability curves are used for tanks, transmissibilities and wells in
prediction – however they are only used in history matching for calculation of
transmissibilities rates.
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Section III
Recommended Processing Steps :
The following steps should be followed in a Material Balance study. For more detailed
advice, try the tutorials in Appendix A.
1. Make certain you have the following data available:
• PVT,
• Production history,
• Reservoir average pressure history, and
• All available reservoir and aquifer data.
2. Enter the data. At every step check the validity and consistency of the data (PVT,
Pressure History, Production, etc.) * This is the most important step. *
3. If you choose to enter the production history well by well, make sure that all wells
belong to the same tank. * This is the most common mistake. *
4. Find the best possible match using the program's non-linear regression the
'Analytical Method'.
5. Confirm the quality and correctness of the match, using the 'Graphical Method'.
6. Run a simulation to test the validity of the match.
7. Then and only then, go to Production Prediction.
8.1 MBAL Graphical Interface
This version of MBAL uses a graphical interface to facilitate the modelling of the reservoir.
The new interface simplifies the task of building a model by letting you sketch the various
components of the reservoir. All the reservoir components such as tanks, wells and
transmissibilities (communication between tanks) are represented by unique graphical
objects which may be easily manipulated on the screen. As components are added, the
relevant input screens and fields are displayed prompting you to enter the appropriate
data.
Figure 8.2:
Material Balance Tool Graphical Interface
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When you open an existing file, the program will place the reservoir components in the
same position as when the file was last saved. This sketch may not be entirely adequate
and can be altered to suit your preferences. Read the following sections for an
explanation on adding, moving and deleting a graphical object. As the MBAL program is
backward compatible you will have access to existing files from previous versions of Mbal.
8.1.1
Manipulating Objects
The objects that can be added in the graphical plot include:•
•
•
•
•
Tanks
History Wells – these are wells that can own production data which can then be
allocated to tanks on a fractional basis.
Prediction Wells – these are wells that can be used in a production prediction
Transmissibilities – used to model the interface between tanks
IPRs – used to model the interface between a tank and a prediction well
Adding Objects
When opening a new data set or adding a component to an existing data set, the
component must first be created.
To add a new component using the icon bar:
• Click the appropriate component button to the left of the main screen. (E.g.: Add
Tank.) The cursor should change to the shape of the object on top of a crosshair. Next, place the cursor anywhere on the screen and click again. Each
component object has a different shape. MBAL currently uses simple squares to
represent tanks, diamonds to represent transmissibilities, and circles to represent
the wells. The data input screen for the selected component will appear. Enter
the appropriate information and click Done. If you click Cancel by mistake, MBAL
will discard the new object.
➲
If you click on the well button it will add a history well if the production history by
well option is selected in the options dialog. If production history by tank option is
selected then the well button will create a history well. If in doubt, use the menu
option as described below.
To add a new component using the menu:
• Select Input
XXX Data (For e.g.: Tank Data).
The relevant input data parameter screen will appear. Click the
button to the
right of the component name. When creating a new object, MBAL automatically
provides a default name for the component selected (E.g.: Tank01). The data
input screen for the new component will appear. Enter the appropriate
information and click Done. If you click Cancel by mistake, MBAL will discard the
new object.
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To add a new component which is a copy of an existing component using the menu:
•
Select Input
XXX Data (For e.g.: Tank Data).
The relevant input data parameter screen will appear. Select the component that
you wish to copy. Click the
button to the right of the component name. When
creating a new object, MBAL automatically provides a default name for the
component selected based on the existing component (E.g.: Tank01-a). The data
input screen for the selected component will appear with a copy of the original
component. Edit any parameters which you wish to be different from the original
component and click Done. If you click Cancel by mistake, MBAL will discard the
new object.
Deleting Objects
To delete a component, double-click the appropriate component object. MBAL displays the
button to the right of the
data input parameter screen for the selected object. Click the
component name.
➲
View the input data carefully and double-check the object to be deleted. Deleted
components cannot be re-instated. If you do not want to include a component in
later calculations, disable the component instead. See “Viewing Objects” for more
information. Alternatively use the Pop-up Menu. Refer to Graphical Interface Popup Menu for more information..
Moving Objects
Once component objects have been created, manipulating its position on the screen is
very easy. To move an object, press the Shift key and click on the object to move.
Holding down the Shift key drag the object to its new position on the screen.
Alternatively, click on the Move button. The cursor should change to a shape with four
arrows directed to the points of a compass. Place the cursor over the object to move, click
the left mouse button and drag the object to a new position (keeping the left mouse button
down). Release the left mouse button when it is moved to the new position.
Connecting / Disconnecting Component Objects
Connecting the appropriate components together is simple and straightforward. To
connect components together, press the Ctrl key and click on the first object to connect.
Holding down the Ctrl key and mouse button draw a line between connecting objects.
Alternatively, click on the Connect button. Move the cursor over the first object to connect
and click the left mouse button down. Holding the left mouse button down, drag the cursor
to the second object and release the mouse button.
If you attempt to connect two inappropriate components, MBAL will not draw a line. If you
connect two tanks, Mbal will automatically create a transmissibility object between the two
tanks. If you connect a prediction well to a tank, Mbal will automatically create an IPR
object between the prediction well and the tank.
To disconnect objects, repeat the same procedure for connecting objects.
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Enabling / Disabling Objects
Disabling or switching off objects is useful for excluding an object from further calculations
or predictions. To disable an object simply check the ‘Disable’ option to the right of the
object field name in the relevant Input Parameters window.
Alternatively, display the object popup menu by placing the cursor over the object to
enable/disable and click the right cursor button. From the popup menu, select
disable/enable.
All similar objects in the data set appear by name in a column to the right of the input
window. Disabled objects appear as dimmed entries and are indicated by an ‘X’ in the
Input Parameters window and MBAL display window. To enable an object, de-select the
‘Disable’ option. Enabled objects are indicated by a check mark in the Input Parameters
window.
Editing Objects
If you double click on an object, the data input dialog for that object will be displayed.
Alternatively, the input dialog can be displayed by selecting the appropriate menu option.
8.1.2
Viewing Objects
In the unusual situation where you may have a large number of components and data to
manipulate, MBAL has a facility that allows you to view and handle the data more
efficiently. These editing facilities are located under the View menu.
Show Main Plot
Use this option to clear the graphical display screen. All objects and connections are
erased from the screen but not deleted. Use this option if you wish to switch off the
graphical interface or remove the sketch from the screen. A check indicates the option is
‘On’.
Show Tanks
Use this menu option to display all the tank components in your data set. A check
indicates the option is ‘On’. Turning the option ‘Off’ hides all the tanks in the current data
set. By turning ‘Off’ the other components in the data set, this facility can be used to
confine the display to the objects you want to view or edit.
Show History Wells
Use this menu option to display all the history well components in your data set. A check
indicates the option is ‘On’. Turning the option ‘Off’ hides all the history wells in the current
data set. By turning ‘Off’ the other components in the data set, this facility can be used to
confine the display to the objects you want to view or edit.
Show Prediction Wells
Use this menu option to display all the prediction well components in your data set. A
check indicates the option is ‘On’. Turning the option ‘Off’ hides all the prediction wells in
the current data set. By turning ‘Off’ the other components in the data set, this facility can
be used to confine the display to the objects you want to view or edit.
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Show Transmissibilities
Use this menu option to display all the transmissibilities components in your data set. A
check indicates the option is ‘On’. Turning the option ‘Off’ hides all the transmissibilities in
the current data set. By turning ‘Off’ the other components in the data set, this facility can
be used to confine the display to the objects you want to view or edit.
Show All
This menu option displays all objects. Use this option to display all hidden components.
Hide All
This menu option hides all objects. Hidden objects are included in the calculations if they
are enabled.
Arrange Icons
Use this menu option to rearrange the graphical display. Objects are arranged in a more
orderly manner to facilitate editing and viewing. Use this option to redraw the sketch
model after deleting objects from the data set. When updating older data sets to the new
version, use this option to draw a sketch of the existing components in the data set.
When are Objects Hidden or Disabled ?
The input dialog for each object type displays a list of the current objects in a column to the
right of the input dialog. The only exception is for a single tank model where there is no
need to display a list as there is only one tank. To view the object data, simply select the
item from the list. MBAL will automatically display the Data Input window for the selected
object. The following markers indicate the current object status:
Object is valid and enabled.
X Object is disabled.
This object will not be included in any of the calculations.
ø
Object is invalid but enabled.
Go to the object Input Parameter window and click Validate to pinpoint the
errors. Invalid object names will be highlighted in RED on the program plot
window.
Objects that are hidden are not shown in the main program plot window. To determine
which objects are hidden choose the View menu. Objects shown on the plot are indicated
by a check mark in the menu. If no objects are marked, choose View - Show All to display
all the entered items in the file. Hidden objects are included in the program calculations.
Hidden objects may also be disabled. Hidden objects that have been disabled will not be
included in the calculations.
Disabled objects are displayed in the main program plot and indicated by a grey object. To
enable an object, go to the input dialog for the object type and select the required object
from the list. Disabled objects are indicated by a check mark in the Disable option field.
To enable an object remove the mark. Disabled objects are not included in the program
calculations.
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8.1.3
8-9
Validating Object Data
The MBAL smart data validation system of this version has been enhanced to allow the
user to move freely within the input section of the program, even if the data entered are
invalid. Previous versions of the program would not exit an input dialogue if any of the
input fields were in error. This version now allows you to exit a window and continue to the
next dialogue box, but disables all remaining calculation menu items while any of the input
data remain invalid. As the program no longer automatically indicates the field(s) in error,
a Validate button has been added to most input screens. When the Validate button is
clicked, the program directs the user to the invalid field and displays a short error
message. The Validate button will only appear on input screens containing invalid data.
You will note that data input has now been divided into tabs or data sheets. If the error is
not readily apparent, click the button to start the validation procedure. MBAL will guide you
to the incorrect field. Enter the correct data and click validate again. If the data is
acceptable, or falls within the data ranges entered in the Units system, the validate
command button will disappear. Where data is incorrect, MBAL will prompt you with an
error message.
To view the results of the validation procedure select Input - Input Summary to display a
validation table. This table will indicate each object entered in the data set by name and
highlight the tabs in error. For easy identification, tabs that contain errors are highlighted
in RED. To view the error, double click the RED highlighted field in the Input Summary
window. MBAL will automatically display the appropriate tab. Click on the validate button
to place the cursor in the incorrect field. Data sheets highlighted in MAGENTA are empty
but not invalid - this is only a warning.
8.1.4
Graphical Interface Pop-up Menu
This version of the MBAL program includes a facility that provides a short cut to editing
objects quickly and easily. To access this facility place the mouse pointer over an object
item on the plot. Click the RIGHT mouse button. A pop-up menu will appear displaying the
following edit options: (to select a menu option use the LEFT mouse button)
Edit:
Delete:
Disable:
April 2001
Displays the Input Parameter menu for the select object item.
Deletes the selected object item. The program will prompt you to confirm
the deletion. Remember deleted items cannot be re-instated.
Disables the selected object item. Disabled objects will be indicated by
an ‘X’ and will not be included in the program calculations.
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8.2 Tool Options
Once you chose Material Balance as the analysis tool in the Tool menu, go the Options
menu to define the primary fluid of the reservoir. This section describes the 'Tool Options'
section of the System Options dialogue box. For more information on the User Information
and User Comments sections, please refer to Defining the System chapter of this guide.
Figure 8.3:
Material Balance Tool Tool Options
To select an option, click the arrow to the right of the field to display the current choices.
To move to the next entry field, click the field to highlight the entry, or use the TAB button.
Input Fields
Reservoir Fluid
• Oil
This option uses traditional black oil models.
•
Gas (Dry and Wet Gas)
Wet gas is handled under the assumption that condensation occurs at the
separator. The liquid is put back into the gas as an equivalent gas quantity. The
pressure drop is therefore calculated on the basis of a single phase gas, unless
water is present.
•
Retrograde Condensate
MBAL uses the Retrograde Condensate Black Oil model. These models take into
account liquid dropout in the reservoir at different pressures and temperatures.
•
General
This option allows a tank to be treated as an oil leg with a gas cap containing a
condensate rather than just a dry gas. In other words, a tank can be treated as an
oil tank with an initial condensate gas cap or as a condensate tank with an initial oil
leg.
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This means that the user can enter a full black oil description of the oil (as would be done
for the old oil case) and a full black oil description for the gas-condensate (as would be
done for the old retrograde condensate case). This allows modelling of solution gas
bubbling out of the the oil in the tank, as well as liquid drop out in the tank from the gas.
The user may still choose to only enter one model i.e. oil or condensate. This will give
compatibility with old Mbal files.
If we have a full oil and gas model, we can calculate oil properties above the dew point
and gas properties above the bubble point. This allows modeling of super-critical fluids.
We still have to define a tank to either be predominately oil or condensate. Their are two
main reasons:-
-
It is convenient to define a tank fluid type from a display point of view. The tank
type controls how we input the fluid in place i.e. OOIP and gas cap fraction of
OGIP and oil leg fraction. It also defines the predominant fluid in the history
matching e.g. gas or oil graphical plots. However these should not effect the
eventual results (apart from that mentioned below). We should get the same
results if we analyze as an oil tank with a gas cap or a condensate tank with a oil
leg.
The tank type defines the wetting phase. This may have an effect on the
calculation of the maximum saturation of the oil or gas phase. For example, the
maximum gas saturation is 1.0-Swc for a condensate tank but is 1.0-Sro-Swc for
an oil tank. This may effect the calculations of the relative permeabilities.
If you switch from an oil to condensate tank, Mbal will automatically recalculate the input
fluid volumes and pore volume vs depth tables assuming that there is both initial oil and
gas.
Whether the tank is defined as oil or condensate, both oil and gas wells can be defined for
a tank. Suitable relative permeabilites can be used to allow production only from an oil leg
or from the gas cap.
If generalise material balance is selected, all calculations are done using total tank
saturations, rather than original oil zone or original gas zone saturations.
Another major change is full tracking of gas injection in the tank. The main benefit is that
production of injected gas can now be controlled by use of recirculation breakthroughs.
Previously, gas production always contained a mixture of original gas and injected gas
based on a volumetric average. Thus as soon as gas injection started, the produced CGR
would start to drop. If no breakthroughs are entered, this will still be the case. However we
are now able to enter a recirculation breakthough. Whilst the gas injection saturation is
below this breakthough, none of the injection gas will be recirculated. This will mean that
injection gas will remain in the tank. The user may also enter a gas injection saturation at
which full recirculation takes place. At this saturation, only injected gas is produced.
Between the breakthough and full recirculation saturation, a linear interpolation of the two
boundary conditions is used.
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Tank Model
• Simple
In this mode, the MBAL runs a single tank reservoir model. If this
model is selected when more than one tank exists, the currently selected tank will
be modelled.
•
Multi Tank In this mode, the MBAL runs a multiple tank reservoir model with
potentially different PVT per tank.
PVT Model
• Simple
In this mode, the program uses a single PVT model.
•
Variable PVT
In this mode, at the start of any material balance calculation that requires PVT
such as history plots, history simulations or predictions, the variable PVT model is
initialised. Each tank is split into layers that correspond to each layer entered in the
PVT description. If the discretisation step size is small enough then more than
one layer will be created for each PVT layer e.g. if step size is 50 feet and the PVT
layer is 200 feet then 4 layers will be created in the tank. The top of the top layer
starts at the initial GOC and the bottom of the bottom layer is at the initial WOC.
The oil volume of each layer is stored.
Each time we require the average fluid properties for the tank, MBAL calculates
the fluid properties of each layer - the pressure and temperature are calculated
taking into account the pressure and temperature gradients. A pore volume
weighted average of each oil property is then calculated. Gas properties are taken
from the top layer and water properties from the bottom layer.
For prediction wells, the fluid properties are taken from the layers at the well
perforations.
As each calculation progresses with time, the layer depths are recalculated. The
top of the top layer is moved to the new GOC and the bottom of the bottom layer is
moved to the new WOC. The other layer positions are then recalculated between
the GOC and WOC given the oil volume in each layer and the current fluid
properties.
At each time step, MBal removes oil from layers at the perforation depths of
prediction wells and history wells. This means that these layers will shrink in
height. Note that this is not possible for history wells with the multi-tank option this is because we do not know the individual layer rates in this case and there is
no sensible approximation.
When performing the various history matching plots, we have to run a simulation
before each plot to precalculate the average PVT properties.
Production History
• By Tank
This option requires you enter the production history for the each tank.
The tank production history can then be used for history matching.
•
By Well
This option should be used if you have production history per well and
the wells either take production from more than one tank or more than
one well takes production from a single tank. In this case, you will
have to enter the production history for each well and also the
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allocation factor to each tank – Mbal will then calculate the production
history for each tank which can then be used in history matching.
Compositional Tracking
•
•
Yes In this mode, the history simulation and production prediction will track the
composition in the tanks and calculate compositions produced by each well.
No Select this mode if no composition is required.
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8.3 Input
The following sections describe the MBAL program Input menu.
8.3.1
Well Data
This option is enabled only if you chose the By Well option of the Production History field in
the Options menu. The Well Parameters dialog box is used to enter the pressure and the
cumulative production or injection history for a well or group of wells.
8.3.2 Setup
To access the Well Parameters dialog, select the Input - Wells Data menu and click on the
Setup tab. A screen similar to the following will appear:
Figure 8.4:
Well Input Data - Setup
Select a well from the list to the right of your dialog. Next, select the well type from a drop
down list containing a variable selection of flow types. The well type selected determines
the remaining data sheets to be entered. Data sheets containing invalid information for
the well type selected will automatically be highlighted RED. Press Validate to run the
validation procedure and pinpoint the error. If no further data is required for the well, the
other tab(s) may be accessed.
Input Fields
Well Type
Define the flow type of the well selected in the Setup data sheet.
Perforation Top (for Variable PVT only)
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Defines the depth of the top of the perforation where the well perforates the tanks.
Note that for the current release we assume the same perforation heights for all
the tanks that intersect this well.
Perforation Bottom (for Variable PVT only)
Defines the depth of the bottom of the perforation where the well perforates the
tanks. Note that for the current release we assume the same perforation heights
for all the tanks that intersect this well.
Creating a new well:
If you want to create a new well, click the
button. Enter a well name of your choice in
the 'Name' field, select the well flow type and supply the rest of the data for the well.
Alternatively, you can create a new well which is a copy of an existing well. Select the well
you wish to copy and click the
button. Enter a well name of your choice in the 'Name'
field.
Selecting a well:
To select another well, select a well from the list display to the right of the Well Data
window. Click to highlight the well name, or select the list box and use the ↑ or ↓ arrows to
choose a well. You can also select a well by typing the first letter of the well name. If
more than one well begins with the same letter, type the same letter again to select the
next item.
Deleting a well:
To delete a well from the list, first call up the desired well and display its data sheet on the
screen. Click the
command button. MBAL will ask you to confirm the deletion.
Command Buttons:
Import This option is used to import a number of wells and their production data
from a Production Analyst (*.REP) file. If some wells already exist it will
simply append the wells to the end of the list. MBal will ask you if you wish
to overwrite or skip a well if one in the PA file is also currently stored in
Mbal.
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8.3.3 Production / Injection History
To access the production/injection history, choose the Input - Wells Data menu and select
the Production History tab. For existing wells, enter the cumulative production plus the
static pressure in each well’s drainage volume where available. Production data can be
entered even when no pressures are available.
Figure 8.5
Well Input Data - Production
History
The various well production tables may later be consolidated using the 'allocation factor'
on each table which allows the entire, part of, or none of the production / injection history
to be allocated to the tank. It will also attempt to calculate the tank pressure using the well
static pressures. This is done in the Production History tab of the tank dialog (See section
Tank Production History for more information.)
➲
The production/injection, GOR and CGR entered must be cumulative. Note that
Cumulative GOR = Cum Gas / Cum Oil. Refer to section 8.3.11 for more information.
Command Buttons :
Import This option is used to import production data from an external file. Note
that if any production data exists for the current well, you will be asked if
you wish to replace the existing data or append to the existing data. This
file can either be:An ASCII file where you must specify a filter to define the columns in the
file and how they translate to the MBal data columns.
A Petroleum Expert's *.HIS history file.
An ODBC data source.
A Production Analyst (*.REP) file. This file can contain production data for
a number of wells. MBal will search for the well name in the file that
matches the currently selected well - if it finds one then it will import the
production data for that file.
Plot
Displays a plot where you can view a graph of the production history data
for the current well.
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This option can be used to report a listing of the production history data
for the current well.
8.3.4 Production Allocation
This tab is used to allocate the well production to the different tanks. This enables the
program to consolidate the tank production history. To access the production allocation,
choose the Input | Wells Data menu and select the Production Allocation tab. A screen
similar to the following will appear.
Figure 8.6:
Well Input Data Production Allocation
First select the producing tanks:
The Producing From list shows which tanks are connected to the current history well. You
can connect/disconnect tanks to the current well by selecting or deselecting the tank in the
Producing From list. To connect a tank, highlight the tank in the Producing From list. The
tank will be added to the allocation table. To disconnect a tank, de-select the tank name in
the list. This will remove the tank from the table.
Next allocate a production fraction to each well:
Allocation Fraction
The fraction of the well production or injection history to be allocated to the tank.
Defines the multiplying coefficient to use for this well, when the well histories are
consolidated. Any value between 0 and 1 is valid. 1.0 allocates the complete well
production /injection to the tank. 0.0 switches this well off completely.
If this fraction changes over time, enter more than one row in the table. Each row
should define the time at which the allocation factor takes effect.
(See 'Reservoir Production History'.)
Use the Normalise button to automatically change the allocation factors to obtain a total
allocation of 1.0. This is done by raising or lowering all the factors by the same proportion
as required.
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Section III
8.3.5. Tank Parameters
This input data sheet screen is used to define the different tank parameters that are
applied in the calculations. If some of the parameters are unknown just enter an estimated
value, the purpose of the program being to quantify more accurately most of these
parameters.
To access the reservoir parameters screen, choose Input
Tank Data and select the Tank
Parameters tab. The following dialog box is displayed:
Figure 8.7:
Tank Input Data Tank Parameters
Input Fields
Tank type
For the General fluid model, this option can be used to specify the tank as
predominantly oil or condensate. This will effect how the input data is specified and
define the wetting phase used in the relative permeability calculations. It also effects
the form of the history matching.
If necessary, this option allows the definition of a water tank. A water tank can be
used to connect several hydrocarbon tanks to the same aquifer. To do so, connect
all the hydrocarbon tanks to the water tank and select an aquifer model for the
water tank. The pore volume of the water tank should be at least double the pore
volume of the biggest hydrocarbon tank connected to it.
Otherwise the tank type should be left as the default which is the same as the
system fluid type selected in the options dialog.
Temperature
This parameter will remain a constant throughout the calculations. The program
assumes the tank temperature does not change with production and injection.
Initial Pressure
Defines the original pressure of the reservoir and is the starting point of all the
calculations.
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Chapter 8 - The Material Balance Tool
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an oil tank with an initial gas cap, make sure the initial pressure of the tank
➲ Inequals
the Bubble Point pressure calculated at reservoir temperature in the PVT
section of this program. The program will display an error message when this is
not the case. You can ensure that the Bubble Point pressure is equal to the Initial
pressure by using the 'Matching' facility of the PVT section. The only exceptions to
this rule are if controlled miscibility has been selected and the remixing factor is
zero or if generalised material balance is being used. In these cases a gas cap
can exist even with the initial pressure above the bubble point.
Porosity
Defines the reservoir and the aquifer average porosity.
Connate Water Saturation
This parameter is used in the pore volume and compressibility calculations.
Water Compressibility (This parameter is optional)
The user has the choice of entering a water compressibility or let the program use
internal correlations. This water compressibility is also used for the aquifer model
connected to this tank.
•
If entered, the program will assume the water compressibility is do not change
with pressure.
➲
•
When the water compressibility is specified, the program back calculates
the water FVF from the compressibility. In this case, the FVF water
correlation used and displayed in the PVT section is ignored. This is to
avoid inconsistencies between different computations in the program,
some using the water compressibility (Graphical and Analytical Methods),
the others using the rate of change of water FVF (Simulation and
Prediction).
If left blank, a 'Use Corr' message is displayed which indicates the program will
do one of the following during the calculations:-:
- If the PVT Tables are in use, and if some values have been entered in the
Water Compressibility column of the PVT Tables, the program will
interpolate/extrapolate from the PVT tables.
- If the PVT Tables are not used, or if there is no data for this parameter in the
PVT tables, the program will use an internal correlation to evaluate the water
compressibility as a function of temperature, pressure and salinity. The
correlation results can be read in the calculation screens or reports.
Initial Gas Cap (OIL Tanks Only)
Defines the original ratio of the volumes occupied by the gas and oil at tank
conditions. It can be defined as m = (G * Bgi) / (N * Boi) where G and N are volume
at surface.
This parameter will be disabled if the Initial Pressure is above the Bubble Point
Pressure calculated by the PVT section at Tank Temperature.
To enable this field, make certain the Bubble Point Pressure matches the Initial
➲ Pressure.
Refer to the Initial Pressure parameter above.
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8-20
Initial Oil Leg (CONDENSATE Tanks Only)
Defines the original ratio of the volumes occupied by the gas and oil at tank
conditions. It can be defined as n = (N * Boi) / (G * Bgi) where G and N are volume
at surface. Note that an initial oil leg can only be used if the General fluid model has
been selected in the Options menu.
Original Oil/Gas in Place
This is usually the parameter you are interested in. If you do not plan to use the
History Matching facility of this program, a value, as accurate as possible, must be
entered. If you plan to use the History Matching section, enter an approximate value
as every Aquifer Influx model will give a different value for this parameter.
Start of Production
The time of start of production.
Permeability (Gas Coning Only)
This is only required if the gas coning option for oil tanks is switched on. This is
simply the average radial permeability of the tank.
Anisotropy (Gas Coning Only)
This is only required if the gas coning option for oil tanks is switched on. This is ratio
of the vertical permeability and the average radial permeability of the tank.
•
Monitor Fluid Contacts
Select this option if the program is to calculate the depth of the Gas/Oil, Oil/Water
or Gas/Water contacts. A check indicates the option is ‘On’. If this option is
selected, you will be required to fill in the table in the 'Pore Volume Fraction Vs
Depth' tab of the Tank Input dialog.
In predictive mode, this table allows the triggering of gas/water breakthrough on
the depth of the fluid contacts instead of the phase saturations. (See the Well
Type Definition dialogue box).
De-select the option, if no fluid contact depth calculation is to be performed or the
required data is not available.
•
Dry Gas Producers (oil fields only)
Select this option, if the primary gas cap is being produced by dry gas producer
wells. It must also be selected if you also wish to select the Use Total
Saturations option - see below for more information on this option.
When this option is selected, the initial pore volume is considered to be the gas
cap + the oil leg. Therefore the initial gas saturation in the pore volume is
(1-Swc) *m / (1 + m) with m = (G*Bgi) / (N*Boi).
Mbal is therefore applying material balance to the total pore volume (oil leg plus
gas cap) so it can successfully model oil being pushed into the initial gas cap. If
oil never encroaches into the initial gas cap, this option will make no difference to
the results.
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Chapter 8 - The Material Balance Tool
➲
•
8-21
Important Note:
The program considers that the pore volume is the original oil pore volume
for the purposes of calculation of relative permeabilities. Therefore the
initial gas saturation used for calculation of relative permeabilities is always
zero. If you wish to use total saturations when calculating relative
permeabilities then use Total Saturations (described below).
Use Total Saturations (oil fields only)
This option can only be selected if Has Dry Gas Producers is also selected. As
well as using the total saturations (i.e. gas cap and oil leg) for material balance,
this option will also use the total saturations when calculating the tank rate from
the relative permeability curves. This will allow immediate production of free gas
from the gas cap rather than having to wait until gas breakthrough e.g. cases
where the well is also perforated in the gas cap. If the General fluid model has
been selected, total saturations are always used so this option is forced to be on.
➲
Important Note:
Input saturations for the tank data must be entered relative to the total
system - not the oil leg.
•
Gas Coning (oil fields only)
This option can only be selected if Use Total Saturations and Monitor Contacts
are also selected. If selected, you will be able to select gas coning for any of the
layers connected to this tank in the Production Prediction - Well Definition
dialog. If gas coning is used, the production prediction will calculate the GOR for
a layer using a gas coning model rather than using the relative permeability.
Water cut will still be calculated from the relative permeability curves. The gas
coning model can be matched for each layer in the Production Prediction Well Definition dialog. The gas coning model is taken from reference 32, see
Appendix B.
•
Gas Storage (gas fields only)
Select this option, to model gas injection into a tank containing water (and gas if
specified). A check indicates the option is ‘On’. In addition You must specify the
Total Pore Volume for the gas storage tank. If there is no gas originally in the
tank, then leave the gas in place field at zero – otherwise enter the amount but
ensure that the down-hole GIP is not greater than the total pore volume.
In prediction you may setup a scheme of injection and production to simulate the
injection of gas for storage and its later retrieval. Mbal will the total saturations to
determine the relative permeabilites. So it is likely that water breakthroughs will
be required on any production wells, particularly if the amount of gas injected is
small compared with the total pore volume.
•
Total Pore Volume (Gas Storage Only)
Enter the total pore volume for gas storage reservoirs as described above.
•
PVT Definition (Multiple Tank Model Only)
Select the PVT definition to use for this tank. If different PVT definitions are used
for different tanks, Mbal treats them in a simple manner. When oil/gas/water
moves from one tank to another, it immediately takes on the properties of the PVT
definition associated with the tank into which the fluid is flowing. This method
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Section III
obviously has limitations if the fluid in the different PVT definitions is significantly
different.
Command Buttons:
Import
This option is used to import a number of tanks and their production
data from a Production Analyst (*.REP) file. If some tanks already
exist it will simply append the tanks to the end of the list. MBal will ask
you if you wish to overwrite or skip a tank if one in the PA file is also
currently stored in MBal.
Enter, or modify the data as required. Then go to the next tab or press Done to accept the
changes or Cancel to quit the screen and ignore any changes.
8.3.6
Water Influx
This screen is used to define the type and properties of the aquifer, if any. To access the
water influx screen, choose Input - Tank Data and select the Water Influx tab. A dialog
box similar to the following is displayed:
Figure 8.8:
Tank Input Data Water Influx
Input Fields
The particular input variables depend of the model, system and boundary type selected. A
description of each variable is only listed if there is some useful additional explanation.
Otherwise please refer to Appendix C which describes the use of each variable within the
Aquifer Functions.
Model
Select one of the different aquifer models available with this program.
Choose None if no water influx is to be included. The remainder of the
screen will change with respect to the aquifer model selected.
System
Defines the type of flow prevailing in the reservoir and aquifer system.
Boundary
Defines the boundary for linear and bottom drive aquifers. Constant pressure
means that the boundary between the hydrocarbon volume and the aquifer is
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Chapter 8 - The Material Balance Tool
8-23
maintained at a constant pressure. Sealed boundary means that the aquifer
has only a finite extent as the aquifer boundary (not in contact with the
hydrocarbon volume) is sealed. Infinite acting means that the aquifer is
effectively infinite in extent.
Radial Aquifers
Reservoir Thickness
This parameter is used to calculate the surface of encroachment of the
aquifer by multiplying it with the radius and encroachment angle.
Reservoir Radius
This parameter is used to calculate the surface of encroachment of the
aquifer by multiplying it with the thickness and encroachment angle.
Outer/Inner Radius Ratio
Defines the ratio of the outside radius to the inside radius of the aquifer
model.
Encroachment Angle
Defines the portion of the reservoir boundary through which the aquifer
invades the reservoir.
Linear Aquifers
Reservoir Thickness
This parameter is used to calculate the surface of encroachment of the
aquifer by multiplying it with the reservoir width.
Aquifer Volume
Defines the amount of fluid in the aquifer. It is used to calculate the aquifer
fluid expansion when reservoir pressure declines.
Reservoir Width
This parameter is used to calculate the surface of encroachment of the
aquifer by multiplying it with the reservoir thickness.
Bottom Drive Aquifers
Aquifer Volume
Defines the amount of fluid in the aquifer. It is used to calculate the aquifer
fluid expansion when reservoir pressure declines.
Vertical Permeability
Defines the aquifer vertical permeability.
Enter, or modify the data as required. Then go to the next tab or press Done to
accept the changes or Cancel to quit the screen and ignore any changes.
See appendix C for details of the water influx equations.
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8.3.7
Section III
Rock Properties
This screen is used to define the Rock properties. To access this screen, choose Input Tank Data and select the Rock Compressibility tab. A dialog box similar to the following
is displayed:
Figure 8.9:
Tank Input Data Rock Compressibility
The rock compressibility’s specified here are used both for the tank model and the aquifer
model connected to this tank (if any).
Input Fields
From Correlation
If this option is selected, the program will use an internal correlation to
evaluate the compressibility as a function of the porosity. The internal
correlation used is expressed as :
-6
if porosity > 0.3 then Cf = 2.6e
if porosity < 0.3 then Cf = 2.6e-6 + (0.3 - porosity) 2.415 * 7.8e-05
Variable vs Pressure
If this option is selected, the program will linearly interpolate / extrapolate
from the data entered in this table. Note that the Cf in this table defines the
change in volume with pressure from the initial conditions. Therefore the
pore volume at the i’th time step in the history simulation or prediction is
given by:PVi = PV0 (1.0 − C f ( P0 − Pi ))
Where PV0 and P0 are the pore volume and pressure at initial conditions.
This formulation means that the results are not dependant on the time
steps selected.
User Defined
If this option is selected, The user must enter the formation compressibility
and the program will assume that the compressibility does not change with
pressure.
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Command Buttons :
Plot
If the rock compressibility is entered as a table of values vs pressure,
this button will display a plot of the table.
Enter, or modify the data as required. Then go to the next tab or press Done to
accept the changes or Cancel to quit the screen and ignore any changes.
8.3.8
Pore Volume vs Depth
This screen is used to define the Pore Volume vs Depth. To access this screen, choose
Input - Tank Data and select the Pore Volume vs Depth tab. A dialog box similar to the
following is displayed:
Figure 8.10:
Tank Input Data Pore Volume vs Depth
This data sheet is enabled only if you have selected the Monitor Contacts option in the
The table displayed is used to calculate the depth of the
different fluid contacts. This table must be entered for variable PVT tanks.
Tank Parameters data sheet.
Pore Volume vs. Depth
The pore volume fraction must be entered, and not the pore volume as the pore
volume changes with the reservoir pressure. The pore volume can also be entered
as acre foot volumes (see the Units System section in Chapter 3).
Important Note:
For oil reservoirs without primary gas cap the pore volume fraction must be
between 0.0 (referring to the top of the structure) and 1.0 (referring to the
initial oil/water contact).
For an oil reservoir with a gas cap, the 0.0 fraction pore volume refers to
the initial gas/oil contact. Gas cap pore volume fraction must be entered
with a negative value.
For example :
Pore
Depth
Volume
(ft)
-2.2
8234
top of structure
0
8343
initial gas/oil contact
.5
8383
1
8412
initial oil/water contact
➲
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Section III
➲
For gas or retrograde condensate reservoirs without a primary oil leg the
pore volume fraction must be between 0.0 (referring to the top of the
structure) and 1.0 (referring to the initial gas/water contact) .
For a retrograde condensate reservoir with a primary oil leg, the 0.0 fraction
pore volume refers to the top of the structure and the 1.0 fraction refers to
the initial gas/oil contact. Oil leg pore volume fraction must be entered with
pore volume values greater than 1.0. The largest depth refers to the initial
oil/water contact
For example :
Pore
Volume
0
1.0
1.5
2.5
Depth
(ft)
8234
8343
8383
8412
top of structure
initial gas/oil contact
initial oil/water contact
If you switch a tank from being of type oil to type retrograde condensate, the pore volume
vs depth table will be recalculated automatically to adhere to the above definitions.
Command Buttons :
Plot
This option displays a plot of the Pore Volume vs Depth table.
Report
This option allows you to produce a listing of the Pore Volume vs
Depth table.
Enter, or modify the data as required. Then go to the next tab or press Done to accept the
changes or Cancel to quit the screen and ignore any changes.
8.3.9
Relative Permeability
Required for production prediction and multi-tank history matching. This screen defines
the Residual Saturations and the different phase Relative Permeabilities. To access this
screen, choose Input
Tank Data and select the Relative Permeability tab. A dialogue box
similar to the following is displayed:
Figure 8.11:
Tank Input Data - Relative
Permeabilities
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Input Fields
Water Sweep Efficiency
The Water Sweep Efficiency is used in the calculation of the depth of the
Oil/Water contact or Gas/Water contact. This parameter is only used in the
calculation of the water contact and can be adjusted to match the measured
depth when the production simulation does not reproduce the observations.
Gas Sweep Efficiency (oil reservoir only)
The Gas Sweep Efficiency is used in the calculation of the depth of the Gas/Oil
contact. This parameter is only used in the calculation of the gas contact and
can be adjusted to match the measured depth when the production simulation
does not reproduce the observations.
Rel Perm From
Select whether the relative permeabilites are to come from
- Corey Functions, or
- User Defined input tables.
Modified
Select from No, Stone 1 or Stone 2 modification. See Appendix C.2 for details
of these modifications.
Residual Saturations
Defines respectively : - The connate saturation for the water phase,
- The residual saturation of the oil phase for water and gas flooding,
- The critical saturation for the gas phase.
These saturations are used to calculate the amount of oil or gas ‘by-passed’
during a gas or water flooding.
End Points
Defines for each phase the relative permeability at its saturation maximum. For
example for the oil, it corresponds to its relative permeability at So = (1-Swc).
Corey Exponents
Defines the shape of the rel perm curve between zero and the end point. A
value of 1.0 will give a straight line. A value less than one will give a shape
which curves above the straight line. A value greater than one will give a shape
that curves below the straight line.
Command Buttons :
Plot
Displays the relative permeability tables in a graph.
Copy
Copies a relative permeability belonging to another object in the
current data set.
Enter, or modify the data as required. Then go to the next tab or press Done to accept the
changes or Cancel to quit the screen and ignore any changes.
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8.3.10 Production History
This tab is used to enter the pressure and cumulative production/injection history of the
tank. It can also be calculated from the well production and allocation data entered in the
Well Data Section using the Production Allocation table described below.
8.3.10.1 Entering the Tank Production History
To access the tank production history, choose Input
Tank Data and select the Production
History tab. A dialog similar to the following will appear.
Figure 8.12:
Tank Input Data Production History
➲
The production/injection, GOR and CGR entered must be cumulative. Note
that Cumulative GOR = Cum Gas / Cum Oil.
Input Fields
Work with GOR (OIL and CONDENSATE Tanks Only)
Check this box if you want to enter the cumulative GOR instead of the gas
cumulative production. When you supply the GOR, the program
automatically calculates the gas cumulative production.
Work with CGR (GAS Tanks Only)
Check this box if you want to enter the cumulative CGR instead of the
condensate cumulative production. When you supply the CGR, the program
automatically calculates the condensate cumulative production.
➲
When they are not known, some reservoir pressure fields can left be blank. These
points can optionally be included in the Graphical and Analytical Methods - in this
case the pressure value will be interpolated.
Be careful, this is not a substitute for good data!
Command Buttons :
Calc Calculates the tank production history rate and pressure. Described in more
detail in section 8.3.10.2 below. Active only for By Well production histories
only.
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Calc
Rate
Calculates the tank production history rate only. Described in more detail in
section 8.3.10.3 below. Active only for By Well production histories only.
Plot
Displays the different production / injection, GOR and CGR data points
versus Time. Click on 'Variable' to select another data column to plot.
Report Allows creation of reports of production history data.
Import Accesses Data Import (Chapter 4) facilities.
➲
The Calc and Calc Rate buttons are not available if the variable PVT model has
been selected. This is because we can not calculate the consolidated pressure
without knowing which wells are producing from which PVT layer - and we do not
know the PVT layer depths over time until we have done a full material balance.
8.3.10.2 Calculating the Tank Production History and Pressure
Clicking Calc will consolidate the different well production tables entered in the Well Data
Production History tabs. The program will combine the input tables using the ‘allocation
factor’ defined for each well. After the calculations, the old production history table will be
destroyed and the new calculated one will be displayed.
At each time step, the cumulative productions are consolidated by adding the cumulative
production/injection of each well corrected for its allocation factor. Refer to Well DataProduction History (Section 8.3) above for the definition of the allocation factor.
To calculate an average pressure, a detailed description of the geology is required.
However if we assume an isotropic reservoir and all the wells start and stop at the same
time, we can estimate a drainage volume proportional to the rate. The average tank
pressure is calculated from the static pressure of each well assuming that:
∑ p *V
p=
∑V
i
i
i
i
i
The Vi are calculated from production history and PVT evaluated at the current reservoir
pressure.
➲
If these assumptions are in any way invalid, then the calculation will yield incorrect
answers. In this case the calculations must be done outside of Mbal.
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Section III
Figure 8.13:
Tank Input Data Tank Production History Calculate
Input Fields
Calculation Frequency
This parameter defines when an average tank pressure and cumulative
productions / injections are calculated.
•Automatic:
The programme performs a calculation every 3 months.
•User
Defined:
The user can define any date increment in days, weeks, months or years in
the adjacent fields.
Command Buttons :
Calc
Performs the production consolidation and average reservoir pressure
calculation.
8.3.10.3 Calculating the Tank Production History Rate Only
Clicking Calc Rate will consolidate the different well production tables entered in the Well
Data Production History tabs. There are two differences between the Calc button and the
Calc Rate. Firstly, it does not calculate the tank pressures. Secondly it does not delete the
existing tank production history table but uses the existing times and pressure at which to
recalculate the rates. The purpose of two buttons is to allow different well allocations to be
used when calculating pressures and rates.
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8.3.10.4 Plotting Tank Production History
Clicking Plot displays the production data from the different wells.
Figure 8.14:
Tank Input Data Plotting Tank Production History
Command Buttons :
The following operations can be performed directly from the consolidated production
history plot screen:
Variables Select variables and well data streams to plot.
Well
Access the well production input screen.
Production
Calculate Re-calculate consolidate production after editing the well productions.
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8.3.11 Production Allocation
This tab is visible only if the by Well option of the Production History field in the Options
Menu is selected. To access, choose Input
Tank Data and select the Well Production
Allocation tab. The Well Production Allocation tab is used to enter the allocation
factors for each tank. These can then be used to calculate the tank production history from
the Well Production History. You may enter allocation factors that change over time.
This tab simply shows a different view of the data entered in the Production Allocation
data page in the Wells Data dialogue. In the Wells Data dialog each table shown is per
well - each column in the table is for one of the tanks connected to the current well. In this
tab, each table shown is per tank - each column in the table is for one of the wells
connected to the current tank.
Figure 8.15:
Tank Input Data Production Allocation
First select the producing wells:
The Wells list shows which history wells are connected to the current tank. You can
connect/disconnect wells to the current tank by selecting or deselecting the well in the
Wells list. To connect a well, highlight the well in the Wells list. The well will be added to
the allocation table. To disconnect a well, de-select the well name in the list. This will
remove the well from the table.
Next allocate a production fraction to each well:
Allocation Fraction
The fraction of the well production or injection history to be allocated to the tank.
Defines the multiplying coefficient to use for this well, when the well histories are
consolidated. Any value between 0 and 1 is valid. 1.0 allocates the complete well
production /injection to the tank. 0.0 switches this well off completely.
(See 'Reservoir Production History'.)
If this fraction changes over time, enter more than one row in the table. Each row
should define the time at which the allocation factor takes effect.
➲
If you do enter/edit the allocation in this tab rather than the Wells Data dialog, be
careful that the allocations factors for each well do not become greater than 1.0 as
you can not see them all on the same table.
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8.3.12 Transmissibility Data
This option is enabled only if you chose the Multi Tanks option of the Tank Model field in
the Options menu. The Transmissibility Parameters dialog box described in the following
section is used to establish the different communication links between tanks.
8.3.13 Transmissibility Parameters
To access the Transmissibility Parameters tab, choose Input
 Transmissibility Data and
select the Setup tab. A screen similar to the following will appear:
Figure 8.16:
Transmissibility Input Data –
Setup
Select a transmissibility from the list to the right of your dialog. Data sheets containing
invalid information for the connection selected will automatically be highlighted RED. Data
sheets containing missing but not invalid data will be highlighted MAGENTA. This is only a
warning. Press Validate to run the validation procedure and pinpoint the error.
Input Fields
Tank Connection
Defines the tanks connected through this transmissibility. Two tanks must be
specified. The connection between the tank can also be created on the main
plot ( see Manipulating Object section above)
Transmissibility
This parameter defines the transmissibility between the
transmissibility model implemented in MBAL is the following.
Kri
Qt = C * ∑ i
* ∆P
tanks.
The
µi
where : Qt is the total downhole flow rate,
C is the transmissibility constant,
Kri is the relative permeability of phase i,
i is the viscosity permeability of phase i,
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P is the pressure difference between the two tanks.
Qt is then split into Qo, Qg and Qw using the relative permeability curves. If
relative permeability curves have been entered for the transmissibility, it will use
those belonging to the transmissibility. Otherwise it will use the relative
permeability curves from the producing tank – this will depend on the sign of the
P.
Certain phases can be prevented from flow by using the Breakthrough
Constraints described below. The relative permeability curves can be corrected
to maintain their shape but starting from the breakthrough saturation.
Permeability Correction of Transmissibility
This factor can be used to correct the transmissibility for changing permeability
in the tank as the pressure decreases. The formula used is:k = k i (1.0 + C f (P − Pi ))
N
where N is the entered value. The permeability decrease is proportional to the
ratio of the current pore volume to the initial pore volume raised to a power.
Breakthrough Constraints
In an attempt to take into account the geometry of the reservoir, one or two
phases can be prevented from flowing until the corresponding phase saturation
reaches a pre-set value. If no breakthrough constraints are required, enter an
asterix in these fields (‘*’).
If a value is entered, it will tell the program that the corresponding phase will not
flow until the phase saturation in the upstream tank reaches this value. When
the sauturation reaches the breakthrough value, the relative permeability will
jump from zero to the value at the breakthrough saturation. If you wish the
relative permeability to increase smoothly after reaching the breakthrough
saturation, select the Shift Relative Permeability to Breakthrough option. This
will shift the relative permeability curve so that it starts at the breakthrough
saturation but maintains the shape of the original curve.
Rel Perms
Used to select which set of relative permeabilites should be used. If Use Tank is
selected then the relative permeabilites are taken from the tank from which the
fluid is flowing. If Use Own is selected then the user must click 'Edit' and enter
a set of relative permeabilites specifically for the transmissibility.
Pressure Threshold
No Threshold
Tanks which are joined by transmissibilities are assumed to have equal potentials.
In other words there is no flow between tanks when they are at their initial
pressures. If the two tanks have different pressures, it is assumed that this was
caused by the tanks being at different depths and the pressure difference is purely
due to hydrostatic effects. As a simulation or prediction progresses and the tank
pressures change from their initial values, MBal always subtracts the initial pressure
difference to remove the effect of hydrostatic pressure differences.
A transmissibility is assumed to allow flow between tanks as soon as the pressure
difference changed from the initial pressure difference. In other words the
transmissibility does not require a significant pressure difference before it allows
fluid to flow.
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Use Threshold with Equal Potentials
This options allows the user to specify a pressure threshold. As the prediction or
simulation progresses, MBal checks if the pressure difference across the
transmissibility is above the threshold pressure. If not, the transmissibility is
modelled as not allowing flow between the tanks. As soon as the pressure
difference increases to above the threshold pressure, the transmissibility is
assumed to have started to flow and we model it as for 'No Threshold' above.
Three important points:Once the pressure difference increases above the threshold and the transmissibility
starts to flow, it will never close again for a particular simulation/prediction. This is
true even if the pressure difference drops below the threshold pressure.
MBal assumes that the pressure threshold works in both directions so it always
checks the absolute pressure difference being above the pressure threshold.
Once the transmissibility has started to flow we do all transmissibility calculations on
the normal pressure difference i.e. we do not subtract the pressure threshold.
Note that for this case, MBal still obeys the rule that tanks are initially at equal
potentials. So any pressure difference is always the current pressure difference
minus the original pressure difference.
Use Threshold with Unequal Potentials
This option is exactly the same as the ‘Use Threshold with Equal Potentials’ except
for the following difference:MBal now assumes that the initial pressure difference in the tanks was not due to
hydrostatic differences but due an actual potential difference which was supported
by the pressure threshold in the transmissibility.
This means that any pressure difference calculated is simply the difference between
the current tank pressures and it does NOT subtract the initial pressure difference.
Use Production History
If need be, flow rates between tank can be obtained from a look-up rather than
computed using the above equation. To do so check the From History check box
and fill in the Production History tab described below. The transmissibility
production history will then be used for a history simulation and any history
simulation at the beginning of the production prediction. It can also be used to
calculate an equivalent transmissibility which can be used in prediction. This option
can be useful if the fluxes between the tank have been calculated in a reservoir
simulator.
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Section III
8.3.14 Transmissibility Production History
To access the Transmissibilities Production History tab, choose Input Transmissibility Data and select the Production History tab. A screen similar to the
following will appear:
Figure 8.17:
Transmissibility Input Data Production History
If the fluxes between the tanks are known, for example from a reservoir simulation run,
such fluxes can be entered in this screen. This data may be used in two different places.
1. If the ‘Use Production History’ check box is checked on the Transmissibility
Parameter screen, the program will use this table as a lookup table to estimate the
fluxes between tanks rather than using the correlation. This can be used in a
history simulation and also in the history simulation part of a prediction.
2. This data can be used to calculate an equivalent transmissibility. The matching is
performed after the MBAL history simulation run.
See section
8.3.15
Transmissibility Matching.
Select a transmissibility from the list to the right of your dialog. Enter the time and
cumulative rates. Although the table has columns for Delta Pressure and the pressure of
the two adjoining tanks, these values are calculated internally by Mbal – so there is no
need to enter anything in these columns. When you reenter this tab, the columns will be
updated automatically.
➲
The production/injection, GOR and CGR entered must be cumulative. Note that
Cumulative GOR = Cum Gas / Cum Oil.
Command Buttons :
Import
This option is used to import production data from an external file.
Note that if any production data exists for the current tank, you will be
asked if you wish to replace the existing data or append to the existing
data. This file can either be:An ASCII file where you must specify a filter to define the columns
in the file and how they translate to the MBal data columns.
A Petroleum Expert's *.HIS history file.
An ODBC data source.
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Plot
This option allows you to plot the production history entered for this
transmissibility.
Report
This option allows you to produce a listing of the production history
data.
Match
This option allows you to calculate a transmissibility equivalent to the
production history. As inputs it uses the production history, the relative
permeability curves of the producing tank and the PVT. See
Transmissibility Matching below for more information.
8.3.15 Transmissibility Matching
This plot can be used to calculate C by matching on production history for that
transmissibility. Note that only transmissibility production history can be used which is
normally only available from reservoir simulators.
The transmissibility can be matched on a transmissibility-by-transmissibility basis. The
following must be performed before matching can take place:-
-
Enter the PVT.
Enter the relative permeability curves. Either enter curves for the transmissibility in
the Setup tab or enter the rel perm curves for both tanks connected to the
transmissibility.
Enter a set of production history points in the Transmissibility Data dialog.
For each point in the transmissibility production history data, MBal plots the total downhole
rate versus the delta pressure between the two tanks. It also calculates the total mobility
for each point. If you click on the Regression menu item, MBal calculates the
transmissibility factor (C) which best matches the data. This is done simply by minimising
the error in the basic transmissibility equation:k
k rg 
k

Qtot = C∆P ro + rw +

µ
µ
µ
w
g 
 o
In this process, the total rate and delta pressure can be simply calculated from the
production history. However the relative permeabilities are more complex. It is done as
follows:-
•
•
Calculate the Fw/Fg/Fo from the production history
Fw/Fg/Fo can also be expressed as a ratio of relative permeabilites e.g.
k rw
Fw =
•
µw
k rw k ro
+
µw µ o
Since relative permeabilites for different phases have opposite trends, there is
always a unique saturation for which such a ratio has a particular value, and thus a
unique set of Kr's.
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Section III
If you wish to increase/decrease the weighting on a data point then double click the point
to display the Match Point Status dialogue. To set the weighting for a group of points at
once, select a range of data points whilst holding down the right mouse button. The Match
Point Status dialogue will be displayed on releasing the mouse button and the new setting
will be assigned to all the points within the area selected.
➲
This method of transmissibility matching does not work if breakthroughs on
fluid contact depths have been used.
Menu Items
Trans.
Select the transmissibility name on which you wish to perform
matching.
Previous Select the previous transmissibility in the list.
Trans.
Next
Trans.
Select the next transmissibility in the list.
Regressi Perform the regression to calculate the transmissibility. This can be
on
either done on the currently selected transmissibility or all
transmissibilities at once.
Sampling If you have a large number of points, this can be used to select ten
equally spaced points by rate or delta pressure. It can also be used to
enable or disable all points.
Save
Use this option to save the last calculated C value to the
transmissibility data.
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8.3.16 Input Summary
This menu option displays the results table of the validation procedure. The table indicates
each object entered in the data set by name. Invalid data sheets and sections in error are
highlighted. For easy identification, data sheets that contain errors are highlighted in RED.
Data sheets highlighted in MAGENTA are empty but not invalid - this is only a warning.
Follow the procedure described in Section 8.1.3 to check data validity.
8.3.17 Input Reports
Please refer to Chapter 5, “Plots and Reports” for an explanation on generating reports.
8.4 History Matching
The following sections describe the MBAL program History Matching menu.
Overview
MBAL provides four separate plots to determine the reservoir and aquifer parameters :
•
Graphical Method
•
Analytical Method
•
Energy Plot
•
Dimensionless Aquifer Function (WD) Plot
All four plots can be displayed individually or simultaneously.
Individually
To open one plot, select the appropriate plot option from the History
Matching menu.
Simultaneously
To open all the plots, select the All option from the History Matching menu.
➲
The Dimensionless Aquifer Function Plot is only available if certain aquifer
models have been selected.
Simultaneous Plot Display
When more than one plot is open is displayed at a time, the following applies:1. Only one plot is active at a time, i.e. has the input focus. This plot will normally
have a blue title bar whereas the inactive plots will have a grey title bar.
2. The menu bar always displays the enabled options of the current active plot. The
menu options vary between plots.
3. Clicking an inactive plot, will make it active.
displayed to reflect the current active plot.
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Section III
4. By default all plots (active and inactive) are synchronised. That is, any change to
the reservoir or aquifer properties will automatically be reflected on all plots.
5. Plots can be de-synchronised by choosing the Windows
Synchronize Plots menu
from the display menu. De-synchronising plots can be useful when the calculations
are too slow (due to the number of data points for example), and the updating of all
plots is taking too long. If this case, only the current active plot needs to be
updated. When the calculations are finished, simply clicking an inactive plot will
refresh / update it.
6. Plots may be tiled or cascaded for an alternate display arrangement.
8.4.1 History Setup
This dialog is used to set various general inputs for the history matching section of the
material balance tool.
History Step Size
During a history matching calculation, Mbal will always perform simulation calculations at
each production history point to be included in the calculation. However, it may also
perform calculations at intermediate steps to ensure that aquifer responses are correctly
modeled. This is particularly important if production history data points are far apart. The
history step size controls these intermediate steps.
If you select automatic, Mbal will perform calculation steps at least every 15 days (more
often if production history points occur more frequently). If you select User Defined then
you can control the calculation step.
If you are running a multi-tank model you will quickly be aware of how much more slow the
calculations are compared to single tank models - this is due to the complications caused
by the transmissibility calculations. If you do not have particularly strong aquifers, you can
significantly speed up the calculations by increasing the calculation step size. In fact if you
enter a very large number (e.g. 1000 days) the calculations will only be done at the times
of the production history data points.
This step size applies to calculation of all the history matching plots, the analytic
regression and the history simulation.
History Matching Plots
Exclude Data Points with Estimated Pressures
This option allows you to exclude any history production data points that have no pressure
values and normally have the pressure value estimated by Mbal.
If you select this option then the estimated points are excluded from all display and
calculations. If the estimated points are to be included in the calculations then the following
rules apply:In the plot display it will use the estimated pressure points exactly as if they were normal
points. Also for multi-tank cases it will also use the estimated points in the initial history
simulation to calculate the transmissibility rates.
In the analytic plot regression the rules are somewhat different. Since the pressures are
estimated, we do not include them in the regression. However for the multi-tank option we
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still use the estimated points in the history simulations that are run every iteration (we only
use the rates for the history simulation anyway) - but we still do not include them in the
actual regression algorithm.
Include transmissibility rates in graphical plots
This option allows you to add the transmissibility rates to the various rates (e.g. F, Qg)
displayed on the graphical plots. Note that the leak rates are always added to the analytic
plot.
8.4.2
Graphical Method
This graphical method plot is used to visually determine the different Reservoir and Aquifer
parameters. To access the graphical method plot, choose History Matching
Graphical
Method. A screen similar to the following is displayed:
Figure 8.18:
History Matching Graphical Method
The following different methods are available:
• For Oil reservoirs
• For Gas/Condensate reservoirs
- Havlena-Odeh,
- F/E versus We/Et.
- (F-We)/Et versus F (Campbell)
- F-We versus Et
-(F-We)/(Eo+Efw) vs Eg/(Eo+Efw)
- P/Z
- P/Z (over pressured)
- Havlena - Odeh (over -pressured)
- Havlena - Odeh (water drive)
- Cole ((F-We)/Et)
- Roach (unknown compressibility)
For a more detailed description of each method, please refer to the appendices.
The aim of most graphical methods is to align all the data points on a straight line. The
intersection of this straight line with one of the axes (and, in some cases the slope of the
straight line) gives some information about the hydrocarbons in place.
For this purpose, a 'straight line tool' is provided to attain this information, . This line 'tool'
can be moved or placed anywhere on the plot. Depending on the method selected, the
slope of the line (when relevant) and it's intersection with either the X axis or Y axis is
displayed at the bottom part of the screen.
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8.4.2.1 Changing the Reservoir and Aquifer Parameters
Reservoir, Transmissibility and Aquifer parameters can be changed without exiting the plot
by clicking on the Input... menu options. On closing the dialog box, the program will
automatically refresh/update the plot(s).
8.4.2.2 Straight Line Tool
The Graphical Method straight line tool is composed of 4 elements: - a straight line, and
three small squares which are used to move the line around the screen.
To translate the line:
click and drag the square at the centre of the line,
To rotate the line:
click and drag one of the squares at the end of the line.
Depending on the Graphical Method used, some squares may be hidden. For example,
the F/Et vs. Et plot for the Oil Reservoir should, when a good match is achieved, show a
horizontal line. In this case, the line 'tool' can only be horizontal and can only be translated
vertically. Thus the squares at the end of the line are hidden.
The line 'tool' always represents the latest set of reservoir and aquifer parameters that
have been entered or calculated. The line] is automatically rotated or translated by the
program to reflect the new values according to the graphical method selected.
➲
Be careful when moving the line 'tool'. Moving the line 'tool' also changes the Oil
or Gas in place value in the Input
Reservoir Parameters dialogue box.
The Best Fit Option:
The 'Best Fit' menu option will automatically find the best fit for the line 'tool', depending on
the Graphical Method used.
Locating the Straight Line tool:
If the straight line 'tool' disappears or becomes to small due to a of change of scales,
double-clicking the centre of the plot will re-scale the line and place it across the plot.
8.4.2.3 Calculations Behind the Plot:
The calculations related to this plot can be viewed or printed by clicking Output | Results
from the plot menu.
−
Only portions of the results can be shown at one time because of the huge amount
of data to be displayed.
−
To browse through the results, use the horizontal and vertical scroll bars.
−
Click the Report button to send the results directly to the printer, the Windows
clipboard or save the results to file.
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Figure 8.19:
Graphical Method – Calculated
Results
The Results screen shows the Expansion, Underground Withdrawal, Aquifer influx etc.
values for each match point.
8.4.3
Analytical Method
This analytical method uses a non-linear regression to assist you in estimating the
unknown reservoir and aquifer parameters. This method is plot based, meaning that the
response of the model is plotted against historical data.
To access the analytical method plot, choose the History Matching
Analytical Method
menu. A screen similar to the following is displayed:
Figure 8.20:
Analytical Method plot
On this plot, the program assumes the tank pressure and some of the productions from
the history entered, and calculates the production of the main fluid. The calculation is done
this way because it is considerably faster to calculate than it would be to calculate the
pressure from all the rates – this is particularly important when doing regression.
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Oil Reservoir
Tank Pressure
Gas production
Water production
Gas injection
Water injection
Calculated Oil production
Values
Water Influx
Inputs
Gas Reservoir
Condensate Reservoir
Tank Pressure
Water production
Gas
production
Water Influx
Tank Pressure
Condensate Production
Water production
Gas injection
Water injection
Equivalent Gas production
Water Influx
The plot always displays at least one curve and the history data points. This curve is:
-
The calculated cumulative production using the reservoir & aquifer parameters of
the last regression (a solid line).
If the tank has an aquifer then a second curve will also be displayed. This curve is:-
➲
The calculated cumulative production of the reservoir without aquifer (by default
this is a blue dotted line although the colour can be changed)
The dotted line (calculated production of the reservoir without aquifer) is plotted
as a safeguard to ensure the validity of the PVT and other reservoir properties.
This line should always under-estimate the production and should always be
located on the left hand side of the historical data points. If it is not the case,
check the PVT properties or tables.
If using a multitank system, another curve will also be displayed. This curve is:-
The calculated cumulative production of the reservoir with aquifer if present but
without the effect of the transmissibilities (by default this is a red dotted line
although the colour can be changed)
However for generalised material balance we do something different. We calculate the
equivalent of a history simulation where the pressures are calculated for the input oil, gas
and water rates. We then plot the calculated pressure and input pressure both versus the
main phase cumulative production (i.e. cumulative oil for an oil tank and cumulative gas for
a gas tank). Since we have to run a full simulation for each calculated line, we do not
display the line without the effect of the aquifer or the transmissibilites.
The data displayed on the plot is for one tank at a time. If you wish to change the tank that
is plotted, use the Tanks, Previous Tank or Next Tank menu items.
➲
As described above, the analytic method attempts to match the calculated and
the input main phase rate. The main phase rate is always plotted on the X-axis
of the plot. Therefore if you wish to check the validity of the match, look at the
error between the data points and the calculated line in the X direction (the
horizontal error) rather than the error in the Y direction (the vertical error).
However if you are using generalised material balance then the pressure is
calculated so in this case examine the vertical error.
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➲
The regression calculation is a slow calculation. One method to speed up the
calculation is to increase the calculation step size. The default is 15 days. To
change this value, select the Production Prediction | Prediction Setup menu.
Change the Prediction Step Size setting to User Defined and enter a large
number e.g. 1000 days. This will cause the regression to only use the entered
times for the calculations instead of using 15 day sub-steps. However it is
inevitable that this will reduce the accuracy of the calculations particularly if there
is a large aquifer or data points are far apart – so it is advised to go back to the
smaller time steps once a reasonable estimate has been found.
➲
If a model is incorrectly matched or the input data is incorrect, the calculated line
can sometimes reverse in the X direction i.e. the cumulative main phase rate
plotted on the X axis can start to decrease. For an explanation, let us consider
an oil tank. If the entered gas rate or water rate is too high to maintain the
entered pressure (even with a zero oil rate), the only solution for the calculation
is to ‘inject’ oil into the tank to maintain that pressure. Therefore the cumulative
oil will decrease and the curve will appear to reverse. This may indicate that the
current estimates of the input tank and aquifer parameters are wrong or the input
production history is incorrect.
➲
For multi-tank. the plot displays one tank at a time. Before plotting the data,
MBal first runs a history simulation with the current model to calculate the
transmissibility rates. These rates are then added to/subtracted from the tank
production history as if it was real production. The tank response can then be
calculated as for a single tank model. Note however that during a regression the
complete multi-tank model is calculated for each new estimates.
Menu Commands
Tanks
Only for multi-tank option. The analytic plot only shows the response for one
tank at a time. Use this menu to select the tank that you wish to view.
Similarly the Next and Previous menu items can be used to change the tank
that is currently plotted.
Input
Access the standard tank and transmissibility edit dialogs. This allows you to
change the input data directly. If any data is changed, then for the single tank
case the plot is recalculated immediately. As the multi-tank calculation can
be very slow, we do not recalculate immediately - when you are ready to
recalculate the plot to show any changes to the tank/transmissibility data,
select the Calculate menu item.
Regression Run the regression calculation.
Sampling
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This menu contains various items for changing the data on which the plot
and the regression work.
Enable All, Disable All act on all points in the current tanks production
history. Disable Estimated Points will disable any points that do not have
any pressure entered and therefore would normally have the pressure
estimated.
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8-46
On Time, On Reservoir Pressure and On Production History are used to
automatically enable only 10 points in the production history. The sampling
will be equally spaced on the quantity in the menu selected.
Show Estimated Pressure Points effects the display only. It is used switch
on/off the display of points with no pressure value.
Exclude Data Points with Estimated Pressures is the same as described
in the History Matching Setup section.
8.4.3.1 Regressing on Production History
To access the Regression dialog box, click the Regression... plot menu option. The content
of this dialogue box depends on the type of reservoir and aquifer selected, the existence of
a gas cap, etc.
Figure 8.21:
Analytical Method - Regressing
on Production History
Running a Regression:
•
Select the parameters you want to regress. For single tank cases, this is done by
selecting the tick box to the left of the parameters. For multi-tank cases, click on
the Yes/No button to the left of the Start column. If you wish to remove (filter) all
unselected parameters from the regression dialog, press the Filter button - press it
again to display them again.
•
Enter the starting value of the regression in the centre column. If necessary, these
values can be reset to the values entered in the 'Reservoir Parameters' and 'Water
Influx' dialogue boxes by clicking the Reset command button.
•
Click Calc.
The program regresses on the So + Sg + Sw = 1 equation. After a few iterations (maximum
500) the program will stop, and display in the right hand column the set of parameters
giving the best mathematical fit.
➲
•
Please note that the 'best mathematical fit' may not necessarily be the best
solution. Some of the parameters may seem probable, others will not.
The regression can be stopped at any time by clicking the Abort command button.
The program will display in the right hand column the best set of parameters found
up to that point.
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•
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For single tanks, the standard deviation shows the error on the material balance
equation re-written
(F - We) / (N*E) - 1 = 0 for oil reservoirs
(F - We) / (G*E) - 1 = 0 for gas or condensate reservoirs
to obtain a dimensionless error term. A value less than 0.1 usually indicates an
acceptable match.
For the multi-tank case the standard deviation is the total error in pressure divided by
the number of points in the regression.
•
To use the regression results for one of the parameters as a starting point for the
button (for single tanks) or the
button (for multinext regression, click the
tanks) in the centre column between the values. The program will copy the value
across.
•
To transfer all the parameters at once, click the
button (for single tanks) or the
button (for multi-tanks) between 'Start' and 'Best fit'.
•
Start a new regression by clicking Calc.
•
Return to the plot by closing the current dialog box. The program will automatically
copy the values in the centre column into the fields of 'Reservoir Parameters' and
'Water Influx' dialogue boxes. The program will then immediately recalculate the
new production. The plot now shows the production calculated using the latest set
of parameters.
Command Buttons
Calc
Start the regression calculation.
Reset
This button re-initialises the regression starting values to the original
set of reservoir and aquifer parameters entered in the Reservoir
Parameters and Water Influx dialogue boxes.
8.4.3.2 History Points Sampling
It is sometime an advantage in the first stages of a study to reduce the number of history
data points used in the regression. MBAL offers a simple tool of automatically reducing to
10 the number points used in the regression. Depending on the menu option selected, the
programme will sample the data based on 'equal' time, cumulative production or pressure
steps.
Select the Sampling menu option followed by one of the sub-options available. The Select
All cancels any sampling previously performed and resets the weighting of all the points to
'medium' (see below).
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Section III
8.4.3.3 Changing the Weighting of History Points in the
Regression
Each data point can be given a different weighting in the Regression. Important and
trustworthy data points can be set to HIGH to force the regression to go through these
points. Secondary or doubtful data points can be set to LOW or switched OFF completely.
Changing Single Points:
Figure 8.22:
Analytical Method - Set Match
Point Status (Single Point)
Using the LEFT mouse button, double-click the history point to be changed. The above
dialogue box appears, displaying the point number selected. Choose as required, the
point weighting (High / Medium / Low) and/or status (Off / On). Points that are switched off
will not be taken into account in the regression or production calculations. Click Done to
confirm the changes.
Changing Multiple Points :
Figure 8.23:
Analytical Method – Set Match
Point Status (Multiple Point)
Using the RIGHT mouse button and dragging the mouse, draw a dotted rectangle over the
points you want to modify. (This click and drag operation is identical to the operation used
to re-size plot displays, but uses the right mouse button.) When you release the mouse
button, a dialogue box similar to the above will appear, displaying the number of points
selected.
All the history points included in the 'drawn' box will be affected by the selections you are
about to make. Choose the points' weighting (High / Medium / Low) and/or status (Off / On)
as desired. Click Done to confirm the changes. If you have no right mouse button, the
button selection can still be performed by using the left mouse button and holding the shift
key down while you click and drag.
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8.4.3.4 Calculations Behind the Plot
The calculations related to this plot can be viewed or printed by selecting Output, followed
by the Results option from the plot menu. Only portions of the results can be shown at
one time because of the large amount of data to be displayed. To view the complete
results, use the horizontal and vertical scroll bars to browse through the rest of the
calculations. Click the Report button to send the results directly to the printer, the Windows
clipboard or save the report to file.
8.4.4
Energy Plot
This plot shows the relative contributions of the main source of energy in the reservoir and
aquifer system. It does not in itself provide the user with detailed information, but indicates
very clearly which parameters and properties you should concentrate on. (i.e. PVT,
Formation Compressibility, Water Influx.).
8.4.5
WD Plot
The WD plot shows the dimensionless aquifer function versus dimensionless time type
curves. This plot also indicates the location of the history data points in dimensionless coordinates.
Linear and logarithmic axes are available.
➲
This plot is only available with some aquifer types.
Changing rD parameters
For Radial Aquifers, the rD parameters (ratio of outer aquifer radius to inner aquifer radius)
can be changed on the plot. You may note some WD curves displayed by the programme
that point to rD values shown to the right of the plot display.
To change the current rD parameters, position the cursor in the value range nearest the
point you want to investigate. Double-click the LEFT mouse button. The program
immediately runs a short regression on the rD to find the type curve passing through the
selected point.
The programme will not calculate rD parameters for points selected below the minimum
displayed rD value. An infinite WD solution curve will be calculated for points selected
above the maximum displayed rD value.
8.4.6
Simulation
This dialog box is used for running a production history simulation based on the tanks and
aquifer models that have been tuned with the graphical and/or analytical methods. The
calculations assume the productions from the history data entered, and iterate at each
time step to calculate the reservoir pressure and water influx. Only the times/dates
entered in the history are displayed, even though the program uses smaller time
increments to calculate.
To access the simulation, choose the History Matching
Simulation menu. The following
dialog box is displayed:
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Section III
Figure 8.24:
History Matching Production Simulation
8.4.6.1 Running a Simulation
On entering this dialog, the results of the last history simulation will be displayed. The
scroll bars to the bottom and right of the dialogue box allow you to browse through the
calculations.
This dialog can also be used to display other results. Each set of results is stored in a
stream. There are always three streams present by default:- Production history
- The last history simulation
- The last production prediction
Copies of the current history simulation calculations can be made using the Save button.
This will create a new stream.
To change the stream displayed, change the selection in the stream combo-box at the top
left of the dialog.
For single tank cases, each stream corresponds to the one and only tank.
For multi-tank systems, the list of streams is more complex. Within each stream there are
additional items called sheets. Each sheet corresponds to a tank or transmissibility. You
may also select a sheet to display in the streams combo-box. The results displayed if you
select the stream (rather than one of its sheets) are the consolidated results i.e. the
cumulative results from all the tanks.
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Command Buttons
Layout Allows you to display a selection of the variables you are only interested in
few of the calculation results. These column selections are also used by
the reporting facility.
Save
Use this button to save the current history simulation in a new stream.
Calc
Click this button to start a new history simulation. A small progress window
with an Abort button will appear in the top right hand corner of your screen.
Press the Abort button at any time to stop the calculation.
Report Allows reporting of the currently displayed stream/sheet to a file, clipboard
or printer.
Plot
Displays a plot of up to two variables from one or more streams or sheets.
Refer to section 8.4.5.2 for information on the plot.
➲
The simulation calculation is a slow calculation. One method to speed up the
calculation is to increase the calculation step size. The default is 15 days. To
change this value, select the Production Prediction | Prediction Setup menu.
Change the Prediction Step Size setting to User Defined and enter a large
number e.g. 1000 days. This will cause the simulation to only use the entered
times for the calculations instead of using 15 day sub-steps. However it is
inevitable that this will reduce the accuracy of the calculations particularly if there
is a large aquifer or data points are far apart – so it is advised to go back to the
smaller time steps once a reasonable estimate has been found.
➲
Make sure a new simulation is run each time the PVT or the main set of
reservoir, aquifer parameters are changed.
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8.4.6.2 Saving Simulation Results
At the conclusion of a history simulation run, you may click Save to save the current run in
memory for comparison with other calculations. The following screen will be presented:
Figure 8.25:
Production Simulation Save Calculation Stream
Data Stream
Displays a list of the saved data streams. By default you will normally get the three data
streams:History (production history entered in the tank data)
Simulation (production history simulation)
Prediction (production prediction)
It also displays any data streams that have been saved (see Add below)
Note that you can change the name of any of the streams (apart from the default streams)
simply by clicking on the name and editing the name.
Description
The program automatically provides a default description name. Enter a new meaningful
description for this prediction/simulation run.
Nb Points
Displays the number of calculated points for the prediction/simulation to be saved.
Command Buttons
Add
Creates a new stream which is a copy of the current history simulation. The
stream is given a default name which you may change.
Replace This can be used to replace an existing stream. Select an existing stream
(not one of default ones) and click Replace. The selected stream will be
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replaced by a copy of the current history simulation. The stream is given a
default name which you may change.
Remove Deletes the selected stream set from the list. You will be prompted to
confirm the deletion.
Click Done to implement the stream changes. Click Cancel to exit the screen and
ignore the changes.
8.4.6.3 Plotting a Simulation
To access the simulation plotting facility, click Plot.
appears:
A screen similar to the following
Figure 8.22:
Production Simulation - Plot
screen
To change the variables plotted on the axes, click the Variable plot menu option. The
following dialog box appears:
Figure 8.27:
Production Simulation – Plot
Variable Selection
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This dialog box allows you to choose the X and Y variables to plot. Two variables can be
selected from the left list column (Y) and one from the right list column (X).
To select a variable item, simply click the variable name, or use the ↑ and ↓ directional
arrow, and use the space bar to select or de-select a variable item. The program will not
allow more than two variables to be selected from the Y axis at one time.
➲
If you have already selected 2 variables for the Y axis and want to change one of
them, first de-select the unwanted variable, and then choose the new plot
variable.
This option allows the user to select the data streams/sheets to be displayed, allowing the
comparison of the simulation and the prediction on the same plot. To select a data stream
or sheet, click on the name of the stream/sheet. The stream/sheet can be unselected by
clicking again on the same name.
8.4.7
Fw / Fg / Fo Matching
One on the main difficulties of running a Production Prediction is to find a set a relative
permeability curves that will give a GOR, WCT or WGR similar to the ones observed during
the production history. The purpose behind this tool is to generate a set of Corey function
parameters that will give the same fractional flows as in the production history at the
saturations calculated while running the simulation.
The relative permeabilities can be generated for the tank, for the individual wells or for the
transmissibilities.
- In order to generate the relative permeabilities for a well, the production history for
this well must be entered in the Well Data Input section.
- In order to generate the relative permeabilities for a transmissibility, the production
history for the transmissibility must be entered in the ‘Transmissibility Data' Input
section and the 'Use Production History' flag must be switched on. Note that the
history simulation has to be run after this input data has been entered. If this is not
done, the history simulation uses the rel perms of the source tank so any Fw/Fg/Fo
match will simply generate the entered relative permeability curves. In order for the
transmissibility relative permeabilites to be used in the prediction, the 'Use Own'
option must be set in the ' Transmissibility Data' Input section after performing the
Fw/Fg/Fo match.
Choose the item to regress on by selecting the tank, transmissibility or the well in the item
menu option.
In a Corey function, the Relative Permeability for the phase x is expressed as :
 Sx − Srx nx

Krx = Ex * 
 Smx − Srx 
where :Ex is the end point for the phase x,
nx the Corey Exponent,
Sx the phase saturation,
Srx the phase residual saturation and
Smx the phase maximum saturation.
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The phase absolute permeability can then be expressed as :
Kx = K * Krx
where :K is the reservoir absolute permeability and
Krx the relative permeability of phase x.
➲
For the purpose of clarity, the following detailed explanation describes the
matching of the water fractional flow in an oil tank.
Mbal’s first step is to calculate the points from the input production history – these are
shown as points on the plot. For each production history point the Sw value is taken from
the value calculated in the production history. The Fw value is calculated using the rates
from the production history and the PVT properties. Now taking into account the capillary
pressures and the gravity’s, the water fractional flow can be expressed as :
Fw =
Qw * Bw
Qo * Bo + Qw * Bw
where :µx is the viscosity,
Qx the flow rate and
Bx the formation volume factor of phase x.
The second step is to calculate the theoretical values – these are displayed as the solid
line on the plot. As for the date points, the water saturations are taken from simulation.
The Fw is calculated from the PVT properties and the current relative permeability curves
using:Kw
µw
Fw =
Kw Ko
+
µw µo
When a regression is performed, Mbal adjusts the Corey terms in the relative permeability
curves to best match the Fw from the data points and the Fw from the theoretical curves.
The other matching types are defined as follows:- For Fg matching in an oil tank, Fg is the gas rate divided by the sum of the gas, oil
and water rates. Note that the gas rate is the free gas produced from the tank –
not the gas produced at surface.
- For Fw matching in a gas tank, Fw is the water rate divided by the sum of the
water and gas rate.
- For Fw matching in a condensate tank, Fw is the water rate divided by the sum of
the water and gas rate.
- For Fo matching in a condensate tank, Fo is the oil rate divided by the sum of the
gas plus oil rate. Note that the oil rate is the free oil produced from the tank – not
the oil produced at surface.
➲
This fractional flow matching tool can only be used if a Simulation has been run.
It is also important to re-run a Simulation each time input parameters are
changed as they will probability affect the saturations and/or the PVT properties.
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8.4.7.1 Running a Fractional Flow Matching
To access the fractional flow matching, choose the History Matching
Fw/Fg/Fo Matching
menu. A plot showing the fractional flow versus saturation will be displayed. No data
points will be displayed if :
•
•
the simulation has not been run,
there is no production of the phases required for the match.
Figure 8.28:
Fractional Flow Matching
Most of the time, particularly after a long production history, the late WCT does not really
represent the original fractional flows. They usually take into account the Water
breakthroughs, and also show the different work-overs done to reduce water production.
These late data points can be hidden from the regression by double-clicking on the point to
remove. A group of points can also be removed by drawing a rectangle around these
points using the right mouse button. The data points weighting in the regression can also
be changed using the same technique. (Refer to the Changing the Weighting of History
Points in the Regression section described above.)
The breakthrough for the saturation that is displayed on the X axis is marked on the plot by
a vertical blue line. This will be taken into account by the regression. The breakthrough
value can be changed on the plot by simply double-clicking on the new position – the
breakthrough should be redrawn at the new position.
Click on Regression to start the calculation. After a few seconds, the program will display
a set of Corey function parameters that best fit your data.
➲
These parameters represents the best mathematical fit for your data, insuring a
continuity in the WCT, GOR and WGR between history and forecast. This set of
Corey function parameters will make sure that the fractional flow equations used
in the Production Prediction Tool will reproduce as close as possible the fractional
flow observed during the history. These parameters have to be considered as a
group and the individual value of each parameter does not have a real meaning
as, most of the time, the solution is not unique.
The set of parameters can be edited by selecting Parameters option from the plot menu.
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The set of parameters regressed can be copied permanently into the data set by selecting
the Save option from the plot menu.
➲
In the case of an Oil reservoir, the water fractional flow should be matched
before the gas fractional flow.
8.4.8
Sensitivity Analysis
This option is used for running a sensitivity on one or two variables. A certain number of
values between a minimum and a maximum can be defined for each variable. For each
combination of values the program will calculate the standard deviation of the error on the
material balance equation rewritten:(F – We)/(N*E) – 1 = 0
for oil. The regression uses the point selected in the analytic method along with their
respective weighting.
Note that this option is not available for multi-tank cases.
To access this option, choose the History Matching | Sensitivity menu. The following
dialog appears.
Figure 8.29:
Sensitivity Analysis
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8.4.8.1 Running a Sensitivity
Select the sensitivity variables by checking the corresponding boxes. A minimum of 1 and
a maximum or 2 variables may be selected at a time. Specify the number of steps the
program is to perform between the minimum and maximum values. Selecting 20 steps will
generate 21 values for the variable from the minimum to the maximum. Selecting 20 steps
for each variable will perform (20+1)*(20+1) runs. If necessary, these values can be reset
by clicking the Reset command button.
Click Plot to start the calculation. After a few seconds, a plot of one of the variables versus
the standard deviation will appear. A sharp minimum indicates the most probable value for
this variable. A flat minimum indicates a range of probable values. Select Variables to
change the variable being plotted.
When two variables are used, the plotting of the standard deviation will also indicate the
uniqueness of the solution. In some cases, the program will show that for each value of the
first parameter, there exists a value for the second parameter that gives the same
minimum standard deviation. This means there is an infinite number of solutions and that
one of the variables must be fixed in order to calculate the other.
8.5 Production Prediction
The production prediction section of the program is used to simulate the reservoir
performances. The program can switch from history simulation to prediction mode at a
date selected by the user.
The model assumes the following:
•
•
•
•
•
•
All the producers are connected to the same production manifold.
All the water injectors are connected to the same water injection manifold.
All the gas injectors are connected to the same gas injection manifold.
All the aquifer producers are connected to the same aquifer production manifold.
All the gas cap producers are connected to the same gas cap production manifold.
The pressure of the five manifolds can be set independently.
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Figure 8.30:
Production
Prediction
Model
Assumptions
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The program provides four different types of prediction:
1.
Reservoir Pressure only from Production Schedule
This mode is not available with Multiple Tanks. In this mode the well and manifold
are completely ignored. Only the tank and the aquifer are taken into account. The
user enters the tank production and injection schedule. The program simulates the
tank and aquifer behaviours.
Input data:
• The tank parameters and relative permeabilities,
• The aquifer type and parameters,
• The description of the fluids injected (optional),
• The production schedule for the main phase (e.g. oil for an oil system, gas for a
gas or condensate system).
• The injection schedule (optional)
Assumptions:
•
The GOR, CGR, WCT, WGR, etc. are calculated from the fractional flows using
the tank relative permeabilities. These values then define the other phase rates
(e.g. water rate for an oil system). There is no notion of breakthrough or
abandonment.
Calculated data:
• The tank pressure and saturations,
• Tank rates and cumulative productions for the other phases.
• Tank average water salinity, gas cap gravity, etc.
➲
2.
Use Prediction Mode 1 to find reservoir pressures for a given production
offtake. This is the classical Material Balance calculation.
Reservoir Pressure and Production from Manifold Pressure
In this mode the user has to enter the manifold pressure schedules. The program uses the
well definitions (IPR’s, TPC’s) to evaluate the performance of each well for given reservoir
and manifold pressures. The program iterates on the manifold pressures until the total
production and injections match the schedule provided.
Additionally, minimum and maximum constraints can be set on the production and
injection rates. When triggered, these constraints supersede the manifold pressure
schedules. For example, if the production manifold pressure specified by the user triggers
the maximum production rate, the program will increase the manifold pressure to satisfy
this constraint, overriding the user input. This facility can be used for example to define a
production plateau followed by a decline.
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Input data:
• The tank parameters and relative permeabilities,
• The aquifer type and parameters,
• The well performance definitions, including IPR’s and Tubing Performance
Curves.
• The constraints on injection and production rates,
• The manifold pressures schedules,
• The well (or drilling) schedule.
Assumptions:
•
The GOR, CGR, WCT, WGR, etc. are still calculated from the fractional flows
using the reservoir relative permeabilities but breakthrough, abandonment,
and/or production constraints can be provided with the well definitions.
Calculated data:
• The tank pressure and saturations,
• Tank rates and cumulative productions for the all phases,
• Tank average salinity, impurity constraints, etc.
• Manifold pressures (if constraint is triggered),
• Individual well performances such as :
• Production or injection rates,
• Flowing bottom hole pressure,
• Flowing or manifold pressure (if rate constraint triggered),
• CGR, GOR, WCT, WGR, etc.
➲
3.
Use Prediction Mode 2 to calculate production forecasts for a given reservoir
and well configuration.
DCQ from Swing Factor and DCQ Schedule (Gas Reservoirs Only)
In this mode the program calculates the maximum daily gas contract that the reservoir can
deliver over the specified periods of time. The program takes into account a seasonal
swing factor entered in the ‘DCQ Swing Factor’ Table (see below), and a maximum swing
factor entered in the ‘DCQ Schedule’ Table (see below). The program also honours
(where possible) the constraints entered in the ‘Production and Constraints’ table. If well
definitions and well schedules are provided, the program calculates the production
manifold pressure (or compressor back pressure) required to meet the DCQ.
Input data:
• The reservoir parameters and relative permeabilities,
• The aquifer type and parameters,
• The well and reservoir performance definitions, including the IPR’s and Tubing
Performance Curves.
• The manifold pressures schedules,
• The constraints on injection and production rates,
• The well (or drilling) schedule,
• DCQ swing factors describe the seasonal variations on a calendar year basis,
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•
DCQ schedule describing the dates at which a new DCQ is started along with
the maximum swing factor.
Assumptions:
•
The WGR is still calculated from the fractional flows using the reservoir relative
permeabilities but, breakthrough, abandonment, and/or production constraints
can be provided with the well definitions.
Calculated data:
• The tank pressure and saturations
• DCQ, tank rates and cumulative productions for all phases,
• Tank average salinity, impurity constraints, etc.
• Manifold pressures (if rate constraints are triggered),
• Individual well performances such as :• Production or injection rates,
• Flowing bottom hole pressure,
• Flowing or manifold pressure (if rate constraints are triggered),
• CGR, WGR, etc.
➲
Use Prediction Mode 3 to determine what contract rate a given reservoir and
well configuration can support.
The MBAL program may be used in prediction mode only. Where this may be the case,
the Production History tab of the Input Tank Data section and the History Matching
section can be completely ignored.
Reservoir Simulation Calculation Technique
At each time step MBAL does the following :
•
•
•
•
Assumes a tank average pressure,
Calculates the relative permeabilities and fractional flow of the 3 phases ,
Calculates the produced GOR/CGR and WOR/WGR.
Calculates the individual well production or injection rates and flowing pressures
based on:
• the PVT fluids ,
• the IPR,
• the tubing performance curve or constant bottom hole pressure,
• the production/injection constraints,
• the production schedule,
• Calculates the water influx for this reservoir pressure and time,
• Calculates the tank overall productions and injections,
• For multi-tanks, calculates the transmissibility rates,
• Calculates the gravity of the gas and water phases,
• Calculates the tank’s new saturations and assumes a new reservoir pressure,
• Iterates until convergence of tank pressure.
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Calculated Properties
During the simulation, the program will always calculate the following properties :
• Tank average pressure,
• Oil, Gas and Water saturations,
• Oil, Gas and Water relative permeabilities based on the saturations,
• PVT properties of the three phases,
• Water and gas fractional flows based on relative permeabilities, dip angle and
PVT,
• Gas gap average gravity, taking into account the gravity of the gas injected and
out of solution (oil reservoir only),
• The gas impurity constraints (for gas storage only), taking into account the H2S,
CO2 and N2 constraints of the gas in place and the gas injected.
• The water average salinity, taking into account the salinity of the water injected
(oil reservoir only).
Calculation and Reporting Time Steps
The Reporting Frequency (or time step - see the Reporting Schedule dialog box) can be
set by the user to determine the times displayed in the results dialogs. However there are
usually extra calculation times between the time steps displayed on the results dialogs or
reports.
•
The prediction step size defaults to 15 days. This can be changed in the
Prediction Setup dialog. Extra calculation times will be inserted based on the
prediction step size.
• Changes in production and constraints. An extra calculation time will be inserted
whenever there is a change in any of the entries in the Prediction Production
and Constraints dialog.
• A calculation time will be inserted if and when the calculation changes from
history to prediction mode.
• A calculation time will be inserted whenever a well is started or shut in as
defined in the Well Schedule dialog.
• A calculation time will be inserted whenever there is a change in any of the DCQ
inputs.
Switching Between History Simulation and Prediction
To run an accurate prediction, the calculation should always be started from day one of the
reservoir producing live. This can be time consuming if you have chosen to run the
prediction based on the well performance definitions. This would require :-
•
the entry of the performance definition of all the wells that have been active
since the reservoir started production,
•
along with their evolution in time (change of completion, stimulation, change of
well head conditions, etc.).
For this the reason the program offers the possibility of running the simulation based on
the Production History from day 1 to a user defined date – this will do exactly the same
calculation as the simulation in History Matching. You can then switch to a Prediction
Mode that uses the well performance definitions provided.
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The variable ‘switching’ date gives you the possibility of an overlap in the last part of the
production history, which allows you to check the validity of the well performance
definitions provided. It also avoids duplicating the entry of the production history if you
chose to run the prediction based on a production schedule. The ‘switching’ date can be
set anywhere between day one and the last day of the production history. See section
8.5.1 ‘Prediction Set-up’ for more details.
8.5.1
Prediction Set-up
This is the first prediction dialog box. It defines the prediction mode :
Figure 8.31:
Production Prediction – Setup
Input Fields
Predict
Defines one of four prediction modes described in the Overview section.
With
Defines the different options for injections/productions. The main purpose of
these options is to simplify the subsequent data entry screens. For example, if
the Water Injection box is not checked, no water injection fields will be
displayed in the rest of the prediction screens.
Options
Check the additional parameters you wish to include in the prediction
calculations.
Prediction Start
This parameter defines when the program will switch from History Simulation
to Prediction.
•
Start of Production
Prediction starts at the first day of production of the tank (specified in
Tank Parameters). For multi-tank systems, if the tanks have different
times for the start of production, it will use the earliest one.
• End of Production History :
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Mbal first uses the production entered in the Production History to
simulate the reservoir behaviour – this will be the same calculation as in
the simulation in History Matching. At the end of the Production History
it switches automatically to prediction mode.
•
User Defined :
The user can defined any date between the Start of Production and the
End of the Production History. This option can be used to compare the
Prediction with the Historical data on the last days of the Production
History, making sure that the well definitions and well schedule perform
properly.
Prediction End
This parameter defines when the program will stop the prediction.
•
•
•
Automatic :
Prediction stops when one of the following conditions is triggered:
• all the wells have stop producing,
• after 80 years of prediction,
• the computer memory is full.
End of Production History :
Prediction stops with the last record of the Production History. This option
is mainly used to check the quality of the prediction against the
Production History before running a full prediction.
User Defined :
The user can defined any date after the Prediction Start defined above.
This option must be used if there is ever likely to be a period with no
production, for example in the case of a gas storage.
Prediction Step Size
The user may specify a reporting step size i.e. how often results for a
prediction are reported. This may only be every year, six months or three
months. However, for accuracy of calculation the prediction must usually be
done with a smaller step size – typically ever two weeks. This option allows
you to specify the maximum step size for a prediction.
So a prediction step will be done for this minimum step size unless another
event (such as a reporting time or change of constraints) occurs first.
•
Automatic
Normally every 15 days – this option should be used unless there is a
good reason to do otherwise.
•
User Defined
Enter the prediction step size in days.
Choose the relevant options and click Done to register the selections or click Cancel to exit
the screen.
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8.5.2
Section III
Production and Constraints
This dialog box describes the production and injection constraints for the tank. The number
and content of the columns will vary depending on the prediction mode and injection
options selected in the Prediction Set-up dialog box.
Each column is linked to a button. Clicking this button will switch the interpolation mode
for the column. When Step is displayed, the parameter will remain constant until redefined.
When Slope is, displayed the program performs a linear interpolation between 2
consecutive values of in the column. This table allows you to define the different column
parameters versus time.
Constraints can be read from ASCII files using the Import button. Please refer to Chapter
4 for further details of the Import Filter.
The following rules apply:
Condition
Meaning
A column is left entirely empty
There is no constraint on this
parameter.
A column contains only one value.
This parameter will remain constant
from
that time onwards
The numbered button on the left hand The corresponding line is ignored
side is depressed
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Figure 8.32
Production Prediction Production and Constraints
Input Fields
Manifold Pressure
Defines the production manifold pressure. This constraint may be overridden
to honour the minimum/maximum oil/gas/water rate constraint.
Oil/Gas Rate
Defines the production rate of the main phase. This is parameter may be
overridden to honour the minimum / maximum Manifold Pressure.
Minimum/Maximum Manifold Pressure
Defines the pressure constraints on the production manifold. When one of
these constraints is triggered, the program changes the Oil/Gas rate in order to
satisfy the constraint.
Minimum/Maximum Oil/Gas/Liquid Rate
Defines the production rate constraints. When one of these constraints is
triggered, the program changes the production manifold pressure in order to
satisfy the constraint. The program checks this constraint against the average
rate.
Voidage Replacement
Defines the fraction of the reservoir pore volume to be replaced with the
injection fluid and can be larger than 100% if you intend to raise the pressure
of the reservoir. The option can be started or altered at any time during the
production of the reservoir and to stop the replacement you must enter a value
of 0%. Voidage Replacement is independent of the Water/Gas Recycling and
Water/Gas Recycling Cut-off constraints. See section 8.5.2.1 Voidage
Replacement and Injection below for more details.
Gas Injection Manifold Pressure
Defines the gas injection manifold pressure. This parameter may be
overridden by the minimum/maximum gas injection rate parameter.
Gas Injection Rate
Defines the production rate of the main phase. This is parameter may be
overridden by the minimum/maximum Manifold Pressure.
Minimum/Maximum Gas Injection Manifold Pressure
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Defines the pressure constraints on the gas injection manifold. When one of
these constraints is triggered, the program changes the gas injection rate in
order to satisfy the constraint.
Minimum/Maximum Gas Injection Rate
Defines the gas injection rate constraints. When one of these constraints is
triggered, the program changes the gas injection manifold pressure in order to
satisfy the constraint.
Injection Gas Gravity
This value is used to calculate the average gas gravity of the gas cap (if any).
It affects the gas cap PVT properties. Leave blank if the injected gas gravity is
the same as the gravity of the gas produced. The original gravity of the gas in
place is defined in the PVT.
Gas Recycling
The Recycling input field signals the program to automatically re-inject this
fraction amount of the gas production. The gas is re-injected without using
Tubing Performance Curve and these injection wells do not need to be
included in the Well Schedule. On the other hand, this re-injection is taken into
account in the calculation of the maximum gas injection rate above.
Gas Recycling Cut-off
Defines the cut-off GOR for the Gas Recycling. The program stopped the gas
recycling if the producing GOR exceeds this value.
CO2, H2S, N2 Mole %
Defines the mole percent of impurity in the gas injected. These percentages
are used to calculate the reservoir average gas content in H2S, CO2, N2. The
original constraints of the gas in place are defined in the PVT section. If these
field are left blank, the program assumes that the content in CO2, H2S, N2 is the
same than the gas produced.
Water Injection Manifold Pressure
Defines the water injection manifold pressure. This parameter may be
overridden by the minimum/maximum water injection rate parameter.
Water Injection Rate
Defines the production rate of the main phase. This is parameter may be
overridden by the minimum/maximum Manifold Pressure.
Minimum/Maximum Water Injection Manifold Pressure
Defines the pressure constraints on the water injection manifold. When one of
these constraints is triggered, the program changes the water injection rate in
order to satisfy the constraint.
Minimum/Maximum Water Injection Rate
Defines the water injection rate constraints. When one of these constraints is
triggered, the program changes the water injection manifold pressure in order
to satisfy the constraint.
Water Injection - Water Salinity
This value is used to calculate the average water salinity of the water in the
pore volume. It affects water compressibility calculation. Leave blank if the
salinity of the injected water is the same than the salinity of the water
produced. The original water salinity is defined in the PVT.
Water Recycling
The Recycling input field signals the program to automatically re-inject this
fraction amount of the water production. The water is re-injected without using
Tubing Performance Curve and these injection wells do not need to be
included in the Well Schedule. On the other hand, this re-injection is taken into
account in the calculation of the maximum water injection rate above.
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Water Recycling Cut-off
Defines the cut-off WCT for the Water Recycling. The program stopped the
water recycling if the producing WCT exceeds this value.
Gas Lift - Maximum Rate
Follows the same rules than the water injection maximum rate above.
Gas Lift- Gas Gravity
This value is used to calculate the PVT properties of the fluid in the tubing.
This parameter only affects predictions using the Well Type Definition and
Tubing Performance Curves.
Enter the relevant information. Click Plot to check the quality and validity of the data.
A Copy button is available in single tank mode. It can be used to copy the current
calculated history simulation results into the corresponding constraint columns. This can
then be used to verify the relative permeability curves by checking if the simulation results
can be reproduced in prediction mode.
8.5.2.1 Voidage Replacement and Injection
When voidage replacement and injection options are selected in the Prediction Setup,
some special rules apply. These rules are true whether the voidage replacement and
injection is selected for gas or water.
The first situation is when both options are selected but there are no injection wells of the
corresponding fluid. In this case, Mbal will calculate the amount of injection fluid required
to replace all the fluid produced for each time step. It then factors this injection rate by the
voidage replacement percentage entered in the Production and Constraints dialog. It will
then inject that amount of fluid into the tank for that time step. No wells are needed to do
this so Mbal always injects the full amount. Note that the voidage is recalculated at each
time step.
The second situation is when both options are selected but injection wells of the
corresponding fluid are currently in operation as specified in the well schedule. In this case
Mbal again calculates the amount of injection needed including the voidage replacement
percentage (as described above). However, rather than simply injecting this amount, Mbal
will set the value as a maximum injection constraint. This means that the full amount will
only be injected if the injection wells can achieve this injection rate - otherwise it will only
inject what it can. If a maximum injection constraint has also been entered then it will
honour the lesser of the two values.
Since we only have one maximum injection constraint for the whole system which can only
be controlled by a single injection manifold pressure, this second method can only be
guaranteed to work if there is only one tank and one injection well.
Note also that both of these situations can occur in a single prediction run as Mbal will
check at each time step if any injection wells are in operation and if a voidage replacement
percentage greater than zero has been entered.
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8.5.3
DCQ Swing Factor (Gas reservoirs only)
This dialog box describes the daily gas contract (DCQ) swing factor over a period of one
calendar year. The instantaneous gas production rate is the product of the DCQ and
Swing Factor.
Figure 8.33
Production Prediction DCQ Swing Factor
Input Fields
Time
Enter the day and month at which the new swing factor should be applied.
Swing factor
Enter the correction to be applied to the DCQ to obtain the production gas rate
from that point in time until the next record.
At the bottom of the swing factor column there is an Average field. This is average value of
the swing factor over the year recalculated by MBal whenever any of the swing factors are
changed.
Note that the program automatically loops back to the top of the table when the last record
is reached (i.e. only one calendar year needs to be described). Enter the relevant
information. Click Plot to check the quality and validity of the data
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8.5.4. DCQ Schedule
This dialog box defines the time at which the program should begin calculating a new
DCQ. The DCQ is maintained constant between two consecutive entries.
Figure 8.34
Production Prediction DCQ Schedule
Input Fields
Time
Defines the next allowed change for a new DCQ. The start time of prediction
must be the top entry.
Max. Swing Factor
Depending on the gas contract, the gas producer may be required to produce
above the DCQ for a short period of time. The maximum swing factor can be
used to insure that the reservoir will be able to produce DCQ * MaxSwing at
any time. In other words, the program makes sure that the potential of the
reservoir is at least DCQ * MaxSwing. You are only required to enter values
when the max swing factor changes. The program maintains the Max. Swing
Factor constant until a new factor is encountered.
Enter the relevant information. Click Plot to check the quality and validity of the data
The timing of the peaks in the Swing Factor and the DCQ schedule breaks may affect the
calculated DCQ. If the maximum swing is required to be produced near the end of the
DCQ contract period, then additional deliverability would be needed if the peak swing
occurred nearer the beginning of the contract period.
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8.5.5
Section III
Well Type Definitions
This dialog is used to define the properties and constraints of a well or group of wells.
Once the well type definitions are established, these definitions are used through the well
schedule to drive the production prediction calculations.
The dialog is split into three data pages:Setup
Define the well type.
Inflow Performance
Enter the parameters for the IPR and layer constraints
Outflow Performance
Enter the parameters for the tubing performance and the
well constraints
Creating a new well definition:
command button in the Well Data
If you want to create more new definition click the
dialog box or press the Add icon button.. Enter a well identifier of your choice in the Name
field, select the well type and supply the rest of the data for the well.
If you wish to create a copy of an existing well definition, first select the well you wish to
copy. The click on the
button. Enter a well identifier of your choice in the Name field.
Selecting a well definition:
To select another well definition, select a well from the list display to the right of the Well
Data window. To pick a well definition, click to highlight the well name, or use the ↑ or ↓
arrows to choose a well. You can also select a well by typing the first letter of the well
name. If more than one well begins with the same letter, type the same letter again to
select the next item.
Deleting a well definition:
To delete a well from the list, first call up the desired well and display its definition on the
command button. MBAL will ask you to confirm the deletion.
screen. Click the
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8.5.5.1 Well Type Setup
Figure 8.35
Well Definition - Setup
Input Fields
Well Type
Defines the flow type of the well.
Tanks (multi-tank only)
Defines which tanks the well is connected to (for multi-tank only). Highlighted tank in the list to indicate that it is connected to the well.
8.5.5.2 Well Inflow Performance
This tab is used to enter the IPR data, relative permeabilities and the layer constraints.
Figure 8.36
Well Definition - Inflow
Performance
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Input Fields
Layers
For multi-layer wells, this list box is used to select which IPR is being edited
in this data sheet.
Layer Disabled
Set this button to on if you wish to temporarily disabled the layer (i.e. the tank
connected to the current well) for the purposes of the calculation. This allows
a layer to be removed from the calculation without deleting it permanently.
Gas Coning
This button is only visible if the gas coning option has been set in the tank
connected to the selected layer. Set this button to on if you wish to use gas
coning for this layer. If gas coning is used, the production prediction will
calculate the GOR for a layer using a gas coning model rather than using the
relative permeability. Water cut will still be calculated from the relative
permeability curves. The gas coning model can be matched for each layer by
clicking on the Match Cone button. The gas coning model is taken from
reference 32, see Appendix B.
Inflow Performance
Defines the well IPR type. The data to be entered for the IPR type selected
will be displayed in the panel below the selection box (e.g. Productivity
Index). For more information on the different models and the associated data
see Inflow Performance (IPR) Models below.
Permeability Correction
This factor can be used to correct the inflow performance for changing
permeability in the tank as the pressure decreases. The formula used is:k = k i (1.0 + C f (P − Pi ))
N
where N is the entered value. The permeability decrease is proportional to
the ratio of the current pore volume to the initial pore volume raised to a
power.
Rel Perms
Used to select which set of relative permeabilites should be used. If Use
Tank is selected then the relative permeabilites are taken from the tank for
the layer. If Use Own is selected then the user must click the Edit button and
enter a set of relative permeabilites specifically for the IPR.
Maximum drawdown
Describes the formation maximum delta P. The flow rate will be reduced to
satisfy this constraint. Leave blank if not applicable.
IPR dP Shift
This field is used to shift the IPR pressure.
Top Perf (TVD) (variable PVT and gas coning only)
This field is used to specify the depth of the top of the perforations for this
layer.
Bottom Perf (TVD) (variable PVT gas coning only)
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This field is used to specify the depth of the top of the perforations for this
layer.
Abandonment Constraints
The layer will automatically be shut-in if one of these values is exceeded. Leave
blank if not applicable. Abandonment constraints can be specified in different ways
e.g. water cut, water-oil contact, WOR. Click the button to select the appropriate
expression. When the Allow Recovery after Abandonment flag is checked, the
layer will resume production if the abandonment constraint is no longer satisfied.
These constraints will be checked independently and in addition to any well
abandonment constraints.
Breakthrough Constraints
The breakthrough constraints are used to prevent the production of a particular
phase until it reaches a particular saturation in the reservoir. This is a control over
and above the relative permeabilities that already control the breakthrough
saturation by use of residual saturations. Breakthrough constraints can be specified
in different ways e.g. water cut, water-oil contact, WOR. Click the button to select
the appropriate expression. Leave blank if not applicable.
When a saturation is below the breakthrough constraint, the layer will not produce
the fluid in question – it will use a relative permeability of zero regardless of the
saturation being higher than the residual saturation in the relative permeability
curves. When the saturation rises above the breakthrough constraint it will start to
flow. The relative permeability will now be found by looking up the relative
permeability curve as normal. This has the disadvantage that the relative
permeability will suddenly jump from zero to the relative permeability at the
breakthrough saturation - not always the physical reality.
Therefore MBal provides a correction to the above method which causes the
relative permeabilites to rise more gradually after breakthrough – the Shift Relative
Permeability to Breakthrough flag. In this case, the relative permeability is still zero
when the saturation is below the breakthrough value. But after the breakthrough
saturation it modifies the relative permeability curves.
In effect it linearly compresses the relative permeability curves. It compresses the
section of the input relative permeability curves from:the residual saturation to the end point saturation
into
the breakthrough saturation to the end point saturation.
This is done by a simple linear translation. It maintains the character of the relative
permeability curve without the sudden large increase at breakthrough.
WARNING:MBI files saved in releases of V4.0 after sub-release 4.0.6.12 failed to save the
relative permeability correction flag correctly. Please check these flags are correct if
you suspect the file may have been written by V4.0. The problem will not occur in
files saved by any other version of Mbal e.g. v3.5, v4.1 or v5.0.
Command Buttons:
Report
Allows reporting of the well definition data to a file, printer or clipboard.
Plot
Displays a graph of the in-flow performance curves to check the
quality and validity of the data.
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Match IPR This option can be used to match the current IPR to one or more sets
of welltest data. See Multirate Inflow Performance for more
information.
Match
Cone
This option can be used to match the gas coning model for this layer
to some test data points i.e. liquid rate and produced GOR.
Calc
Calculates IPR’s and TPC’s intersection on test points provided by the
user.
8.5.5.3 Inflow Performance (IPR) Models
OIL
Straight Line IPR
The productivity index (or injectivity index for injectors) must always be entered. A
straight line inflow model is used above the bubble point. The Vogel empirical
solution is used below the bubble point. There are two further corrections which can
be applied to the IPR calculations (for oil producers only):Water Cut Correction
The Vogel part of the IPR model assumes a water cut of zero. However, in a
prediction, Mbal will correct the Vogel part of the IPR for the current water cut. As
the water cut increases, the Vogel curve is straightened out and hence the AOF
increases. The correction will not have any effect on the straight-line part of the IPR.
The plot of the IPR is normally plotted with a zero water cut. However if you wish to
check the shape of the IPR with a particular water cut, enter the value in the Test
Water Cut field. The IPR plot will now be displayed with the correction for that water
cut.
Mobility Correction
A second assumption on the Straight-line + Vogel IPR model is that the mobility
does not effect the IPR. However if you click the P.I. Correction for Mobility option
on, MBal will attempt to make corrections for change of fluid mobility using the
relative permeability curves. If this option is used you must also enter the Test
Reservoir Pressure and Test Water Cut.
The process is as follows:• Use the test water cut and the PVT model to calculate the downhole
fractional flow Fw.
• Calculate the water and oil saturations that give the Fw. Note we set Sg=0 as
the IPR is already corrected for gas with the Vogel correction.
• Calculate the relative oil and water permeabilities using the relative
permeability curves and the oil and water saturations.
• Calculate a test mobility from:Mt = Kro/(µoBo) + Krw/(µwBw)
The water and oil viscosities are calculated from the test reservoir pressures
and the PVT. We should actually use the absolute oil and water relative
permeabilities but since the only use of the total mobility is when divided by
another mobility, the final results will be correct.
• Whenever an IPR calculation is done:-
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•
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•
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Calculate the PVT properties using the current reservoir pressure and the
PVT model.
Calculate the downhole fractional flow from the current water cut.
Calculate the water and oil saturations that give the Fw. Note we set
Sg=0 as the IPR is already corrected for gas with the Vogel correction.
Get the relative permeabilities for oil and water from the relative
permeability curves.
Calculate the current mobility M as shown above.
Modify the PI using:PI = PIi * M/Mt
In the above method we do not take into account the reduction in oil mobility due
to any increase in the gas saturation. When calculating the Sw and So for a
particular Fw we set Sg=0.0.
If you wish to take the effect of increasing gas saturation into account then
select the Correct Vogel for GOR option. You will also be required to enter a
Test GOR - this is a produced GOR. The process will now be as follows:• Use the test water cut, test GOR and the PVT model to calculate the
downhole fractional flows Fw and Fg.
• Calculate the gas, water and oil saturations that satisfy the Fw, Fg and
So+Sw+Sg=1.0.
• Calculate the relative oil and water permeabilities using the relative
permeability curves and the oil, gas and water saturations.
• Calculate a test mobility from:Mt = Kro/(µoBo) + Krw/(µwBw)
• The water and oil viscosities are calculated from the test reservoir pressures
and the PVT. We should actually use the absolute oil and water relative
permeabilities but since the only use of the total mobility is when divided by
another mobility, the final results will be correct.
• Whenever an IPR calculation is done:• Calculate the PVT properties using the current reservoir pressure and the
PVT model.
• If the Kro, Krw and Krg have already been calculated (e.g. if doing a
prediction) then
• Calculate the current mobility directly as shown above.
• If the Kro, Krw and Krg are not available e.g. IPR plot, IPR matching, well
test calculation
• Calculate the downhole fractional flows Fw and Fg from the current
water cut and produced GOR.
• Calculate the gas, water and oil saturations that satisfy the Fw, Fg and
So+Sw+Sg=1.0.
• Get the relative permeabilities for oil and water from the relative
permeability curves and the oil, gas and water saturations.
• Calculate the current mobility M as shown above.
• Modify the PI using:PI = PIi * M/Mt
Gas
Forcheimer
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The Forcheimer equation expresses the inflow performance in terms of turbulent
and non turbulent pressure drop coefficients expressed as :
(Pr2 − Pwf2 ) = aQ 2 + bQ
In the inflow tab, a (the turbulent pressure drop) is the Non Darcy input field.
Similarly b (the laminar pressure drop) is the Darcy input field.
C and n
This is the most common form of the back pressure equation:
Q = C(Pr2 − Pw2 )n
C and n can be determined from a plot of Q versus (Pr2 - Pw2) on log-log paper.
n is the inverse of the slope and varies between 1 for laminar flow and 0.5 for
completely turbulent flow. This option requires direct entry of C and n in the
inflow tab.
Forchheimer[Pseudo]
This is a variation of the Forcheimer equation using pseudo pressures.
m(Pr ) − m(Pwf ) = aQ 2 + bQ
In the inflow tab, a (the turbulent pressure drop) is the Non Darcy input field.
Similarly b (the laminar pressure drop) is the Darcy input field.
Crossflow Injectivity Index
This field is only accessible if you are using the multi-tank option and only for
producer wells.
Normally if a layer of a production well starts to act as an injector (due to
crossflow), the IPR function is simply extrapolated for negative rates. This can
cause stability problems as the IPR can be very flat as the rate goes negative
(particularly for gas wells).
This field can be used to define a different IPR for negative rates. This can then
be used to reduce the injectivity of a layer and thus give better stability to crossflow.
For oil and water wells, the crossflow injectivity index is the same as the
productivity index.
For Forcheimer gas wells, the crossflow injectivity index is the same as the
Darcy field. The Non Darcy value is set to zero for negative rates.
For C&n gas wells, the crossflow injectivity index is the same as the C value.
The n value is set to 1.0 for negative rates.
If you do not wish to use a crossflow injectivity index (and simply wish to
extrapolate the normal IPR) then enter an ‘*’ in this field.
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8.5.5.4 Multirate Inflow Performance
If one or several well test data are available, the IPR parameters can be regressed upon to
fit the observed rate and pressures. To access the Multirate IPR screen click Match IPR in
the Inflow Performance screen above. A screen similar to the following will appear:
Figure 8.37
Well Definition Multirate Inflow Performance
Input Fields
Reservoir Pressure
Define the reservoir average pressure at the time of the well test.
Water Cut (Oil only)
Define the water cut at the time of the well test.
Well Test Data
Enter all the rates and flowing bottom hole pressures available.
Click Calc or Plot to start the regression. It will only take a second.
Click Done to keep the regressed parameters or Cancel to ignore the calculation.
➲
Before entering data in this tables (a time consuming exercise), please note that
tubing performance curves can be imported from different sources – including
*.MIP files from Petroleum Expert’s PROSPER Single Well Systems Analysis
program. See the Importing Tubing Performance Curve data section that follows.
8.5.5.5 Gas Coning Matching
This dialog is used to match the gas coning model to up to three test data points. The test
points should be from a multi-rate test i.e. at the same tank conditions. You may also
directly edit the match parameters. See reference 32, see Appendix B for an interpretation
of the match parameters.
To access the gas coning match screen, click Match Cone in the Inflow Performance tab
above. A screen similar to the following will appear:
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Figure 8.38
Well Definition Gas Coning Match
Input Fields
Total Liquid Rate
Enter the water plus oil rate for each test point.
Produced GOR
Enter the produced GOR for each test point.
Gas-oil contact
The position of the gas oil contact at the time of the multirate test.
Test Reservoir Pressure
The tank pressure at the time of the multirate test.
Water cut
The water cut at the time of the multirate test.
F2
First matching parameter.
F3
Second matching parameter.
Exponent
Third matching parameter.
Enter the input fields in the Test Points section of the dialog and then click Calc to
calculate the match parameters that best fit the test data.
If only one test point is entered, only the F3 tuning parameter is matched. If two or three
test points are entered, only the F3 and Exponent tuning parameters are matched. If
desired, the unmatched tuning parameters can be edited directly by the user.
It is also possible to calculate the produced GOR for a single liquid rate in the Single Test
Point Calculation Panel. Enter the rate in the Rate field and then click the Calculate
button. The produced GOR for that entered rate will be displayed in the Calc. GOR field.
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8.5.5.6 Well Outflow Performance
This tab is used to enter the outflow performance and the well constraints.
Figure 8.39
Well Definition – Outflow
Performance
Input Fields
Outflow Performance
Defines the well FBHP (flowing bottom hole) Constraints. Select the
appropriate option from the list of constraints currently supported. Click Edit
to get access to the FBHP constraints dialogue box. (See the section on
“Tubing performance curves” for more information.)
➲
The option of Constant FBHP should ONLY be used with extreme caution. It
is likely to give erroneous results for any constraints applied to the system.
Extrapolate TPC’s
This option can be used to extrapolate TPC’s beyond the entered range. If
this option is not selected, then the TPC will remain at its maximum/minimum
value outside of its entered range.
➲
Extrapolated TPC’s frequently give unexpected results. It is recommended
that TPC’s are generated to cover the whole range of rates (WPH’s, GOR,
GLR,...) used by the program during the calculations.
Minimum FBHP
The well is automatically shut-in if the FBHP falls below this value. The well
can be re-started if the FBHP later exceeds this value, due to the start of
water injection for example. Leave blank if not applicable.
Maximum FBHP
The flow rate for injectors will be reduced to satisfy this constraint. Leave
blank if not applicable.
➲
This value is ignored for producing wells as there is no way to increase the
rate. It is only respected for injectors where the well can be choked back to
decrease the FBHP.
Minimum Rate
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The well is automatically shut-in if the calculated instantaneous rate falls
below this value. The well may be re-started after a change in reservoir
pressure due to, for example the start of water injection. Leave blank if not
applicable.
Maximum Rate
If the calculated flow rate exceeds this value, the instantaneous rate will be
reduced to satisfy this constant. Leave blank if not applicable.
Minimum FWHP
The well is automatically shut-in if the FWHP falls below this value. The well
can be re-started if the FWHP later exceeds this value. Leave blank if not
applicable.
Maximum FWHP
The flow rate will be reduced to satisfy this constraint. Leave blank if not
applicable.
Operating Frequency (ESP Producer Wells Only)
The operating frequency of the pump can be specified in this field.
Optimum GLR Injected (Gas Lifted Wells Only)
This field indicates the optimum GLR injected for this type of well. The
program will attempt to allocate this optimum GLR to all gas lifted wells.
Where this is not possible, due to injection constraints, the program will try to
allocate 95% of the optimum GLR to each gas lifted well, and reduces the
allocation by 5% for each subsequent trial.
Abandonment Constraints
The well will automatically be shut-in if one of these values is exceeded.
Leave blank if not applicable. Abandonment constraints can be specified
different ways e.g. water cut, water-oil contact, WOR. Click the
button to
select the appropriate expression.
When the Allow Recovery after
Abandonment flag is checked, the well will resume production if the
abandonment constraint is no longer satisfied. For a well with more than one
layer these constraints will be checked independently and in addition to any
layer abandonment constraints.
Command Buttons:
Report
Allows reporting of the well definition data to a file, printer or clipboard.
Calc
Calculated IPR’s and TPC’s intersection on test points provided by the
user.
8.5.5.7 Tubing Performance
This section describes how to model the performance of the well.
8.5.5.7.1 Constant Bottom Hole pressure
Using this option, the program will maintain the bottom hole flowing pressure constant
throughout the prediction. This option can be used for a quick estimation of injectors’
potential. It should not be used for other than sucker rod pumped producers.
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The option of Constant FBHP should ONLY be used with extreme caution. It is
likely to give erroneous results for any constraints applied to the system.
8.5.5.7.2 Tubing Performance Curves
The Tubing Performance Curve (TPC or VLP) dialog box will appear different depending on
the well type selected (i.e. Natural Flowing, Gas lifted, Injector, etc.). The example below
describes the most complicated of all TPC dialog boxes: Gas Lifted Producer.
Figure 8.40
Well Definition Tubing Performance curves
In this particular example of a Gas Lifted Well, the tubing performance curves table is a 5
dimensional array of FBHP versus WHP, GLR, WCT, GOR and Rates, making altogether
200,000 (10*10*10*10*20) possible FBHP entries. For each WHP,GLR,WCT,GOR and Rates
combination, there will be one bottom hole pressure.
WHP 1
WHP 1
...
WHP 1
WHP 1
...
WHP 1
WHP 1
...
WHP 1
...
WHP 10
GLR 1
GLR 2
...
GLR 1
GLR 2
...
GLR 2
GLR 2
...
GLR 2
...
GLR 10
WCT 1
WCT 2
...
WCT 1
WCT 1
...
WCT 1
WCT 2
...
WCT 2
...
WCT 10
GOR 1
GOR 2
...
GOR 1
GOR 1
...
GOR 1
GOR 1
...
GOR 1
...
GOR 10
RATE 1
RATE 2
...
RATE 20
RATE 1
...
RATE 20
RATE 1
...
RATE 20
...
RATE 20
FBHP 1
FBHP 2
...
FBHP 20
FBHP 21
...
FBHP 40
FBHP 41
...
FBHP 60
...
FBHP
200000
Altogether a total of 50000*5 values that have to entered and stored. To minimise data
entry, reduce the amount of memory space required and speed up the calculations, the
tubing performance curves have been split into 6 tables, displayed as follows:
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10,000
Lists
WHP
200
300
......
......
1000
1500
GLR
200
300
......
......
1000
1300
WCT
0
10
......
......
75
95
GOR
200
400
......
......
900
1400
Rate
1000
2000
4000
5000
...
...
1000
0
FBHP
1234
2345
2897
3190
...
...
4589
These 6 tables comprise:
• 4 tables containing up to 10 values for WHP, GLR, WCT and GOR,
• 1 table containing up to 20 rates,
• 1 2D table containing 10000 (10*10*10*10) lists of 20 FBHP’s.
This means that the GLR, WCT, GOR, and the Rates only need to be entered once. The
FBHP’s displayed on the screen are for a given WCT, GLR and WHP combination. To
display the TPC’s for another combination of WCT’s, GLR’s and WHP’s, depress the table
button above the WCT, GLR and WHP values desired.
Enter data in a TPC table:
1. First enter up to 10 WHP values in the first (horizontal) table.
2. Next enter up to 10 GLR values in the second (horizontal) table.
3. Next enter up to 10 WCT percentages in the third (horizontal) table.
4. Follow with the GOR’s (up to 10) in the fourth lower (horizontal) table
5. Then, enter up to 20 rates in the vertical table for this combination, using the
scroll bar if necessary.
6. Fill in the FBHP table for the given rate and GOR, again using the scroll bar if
necessary.
7. Select another combination of GLR, WCT and WHP by depressing the buttons
above the desired values. A new table of FBHP is displayed.
8. Repeat step 6, until all GLR, WCT and WHP combinations are exhausted.
Importing Tubing Performance Curve data:
To import TPC data from another source, click the Import command. An import dialog box
is displayed prompting you to select an import file to be read. Several file formats may are
available.
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Chapter 8 - The Material Balance Tool
8-85
Figure 8.41:
Well Definition - Tubing
Performance Curves Import
File Type
This field holds a list of import file types. MBAL currently recognises Petroleum Experts’
.MBV and .TPD and GeoQuest ECLIPSE format lift curves. For information on opening a
file, please refer to Chapter 3, “Using the MBAL application”.
When you have selected the appropriate file, press OK. This will open the file and
reformat the data according to the type of file selected. The procedure displays an import
information screen that gives brief details about the file being translated. You will be
informed when the translation is finished.
Command Buttons
Import
Reads a data file generated by other systems containing production
and reservoir pressure data.
➲
Report
Output the current TPC to the clipboard, file or printer.
Plot
Displays the different production / injection, GOR and CGR data points
versus Time. If the IPR has been entered, it also displays the IPR for
the reservoir initial pressure. Click on ‘Variable’ to get a different view
of the TPC’s.
Reset
Deletes the entire contents of the selected input table.
Ensure that the well type has been correctly set before importing Tubing
Performance Curves. Always check the Units used to generate ECLIPSE lift
curves before importing them since the file format does not allow MBAL to
check units.
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Section III
8.5.5.7.3 Cullender Smith correlation
This correlation estimates the pressure drop in the tubing/annulus for a dry gas well. [Ref.
Cullender, M.H. and Smith, R.V.: “Practical Solution of Gas-Flow Equations for Well and
Pipelines with Large Temperature Gradients”, Trans., AIME (1956)207.]
The correlation can be adjusted by entering well test data in the corresponding table and
clicking the Match. button. Two adjustment parameters are then displayed. These
indicate the changes that have been applied to the gravity and friction terms respectively.
GH
* C0 =
53.34
∫
Pw
Ps
 p 
 T * z 
 p 
1000 * ( L / H ) * ( Fz * Q) * C1 + 
 T * z 
2
*dp
2
where:
G
L
H
Q
z
T
d
Fr
=
=
=
=
=
=
=
=
gas gravity relative to air
length of pipe or tubing, ft
vertical elevation difference, ft
flow rate in MMscf/D
Gas deviation factor
temperature, °R
inside diameter of the tubing, in.
friction factor.
C0,C1 are the matching parameters initially set to 1.
Figure 8.42:
Well Definition Cullender Smith correlations
Input Fields
Type of Flow
Select Tubing or Annular flow.
Tubing length
The measured length of the tubing.
Tubing depth
The true vertical depth of the end of tubing.
calculated from the length of the tubing.
An average deviation is
Tubing Head Temperature
An estimate of the well head flowing temperature.
Roughness
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Average roughness of the tubing.
Tubing ID (tubing flow only)
Inner diameter of the tubing.
Tubing OD (annular flow only)
Outer diameter of the tubing.
Casing ID (annular flow only)
Inner diameter of the casing.
➲
This correlation should only be used with dry gas wells. This option is
significantly slower than the Tubing Performance Curves.. If possible
TPC’s should be used rather than this correlation..
8.5.5.7.4 Witley correlation
This correlation estimates the pressure drop in the tubing/annulus for a dry gas well. The
correlation can be adjusted by entering well test data in the corresponding table and
clicking the Match. button. Three adjustment parameters are then displayed.
Qg 2 = ( Ps 2 − CI * Pw 2 ) /( E * (CI − 1))
E = eX
X = 0.006644 * ( Z 2 * T 2 / D 5.23 ) * ( XTUB / DEPTH ) * DD * C1 + (C 2 − 1) * 1e −7
CI = 0.06844 * S * DEPTH /( Z * T ) * C 3
where:
•
•
Qg
= total stream rate
Ps
= Bottom hole flowing pressure
Pw
= Well head flowing pressure
Z
= Gas deviation factor @ T and PW
T
= Reservoir temperature
XTUB = tubing length
DEPTH = tubing vertical depth
For tubing flow
D
= Tubing inner diameter
DD
= 1
For annular flow
D1
= Casing inner diameter
D2
= Casing outer diameter
D
=
D1+D2
DD
= [(D1+D2)/(D1-D2)]3
C1,C2,C3 are the matching parameters initially set to 1.
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Section III
Figure 8.43:
Well Definition - Witley correlation
Input Fields
Type of Flow
Select Tubing or Annular flow.
Tubing length
The measured length of the tubing.
Tubing depth
The true vertical depth of the end of tubing. An average deviation is
calculated from the length of the tubing.
Tubing ID (tubing flow only)
Inner diameter of the tubing.
Tubing OD (annular flow only)
Outer diameter of the tubing.
Casing ID (annular flow only)
Inner diameter of the casing.
➲
This correlation should only be used with dry gas wells. This option is
significantly slower than the Tubing Performance Curves.. If possible
TPC’s should be used rather than this correlation..
Petroleum Experts
Chapter 8 - The Material Balance Tool
8.5.6
8-89
Testing the Well Performance
This dialog box lets the user test the solution points of the IPR’s and TPC’s. This ‘local’
calculation does not affect the rest of the prediction. It is only provided to check the validity
of the IPR / TPC combinations.
Figure 8.44:
Well Definition Well Performance Test
Input Fields
Enter the test conditions (reservoir pressure, manifold pressure, GOR, Water Cut,
etc.) and click the Calc button. The program displays the solution points for each set
of test conditions entered.
To suppress an entry, simply blank out all the fields in the corresponding row. To
add or insert a new record, just enter the record at the end of the list you have
already created. The program automatically sorts the entries.
➲
April 2001
The Well Performance calculator is a convenient tool for calculating well
rates for a given top node pressure. It can also be used in reverse to
determine reservoir pressures. The reservoir pressure is varied until the
model and measured rates agree.
Material Balance Program - Version 6
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8.5.7
Section III
The Well Schedule
This dialog box describes the well schedule. It uses the well definitions previously entered
to define the drilling program of future wells.
Figure 8.45:
Production Prediction Well Schedule
Input Fields
Start Time
Indicates when this well or wells will be started.
End Time
Indicates when this well or wells will be shut-in. Leave blank if not to be shutin.
Number of Wells
Indicates the number of wells involved.
Well Type
Indicates the well type definition involved (one of the well definitions created
in the Well Type Definition dialogue box).
Down-time Factor
Constant defining the relationship between the well average and
instantaneous rate. The average rate is used to calculate the cumulative
production of the well. The instantaneous rate is used to calculate well head
and bottom hole flowing pressures. If 10% is entered then Qavg = Qins * (1 0.1). This constant can be used to take into account recurrent production
shut-down for maintenance or bad weather.
➲
Make sure the first enabled record ‘Start Time’ is less than or equal to the
‘Start of Prediction’ time entered in the Reporting Schedule dialogue box.
The prediction calculation will stop if the ‘End of Prediction’ is set to
‘Automatic’ and there is no flowing well.
To remove an entry permanently, simply blank out all the fields in the corresponding
row. To add or insert a new record, just enter the record at the end of the list you
have already created. The program automatically sorts the entries in ascending
time/data order.
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Records can be switched off or on temporarily by clicking the buttons to the left of
the first column entry fields. When a record is switched off, it is not taken into
account in the prediction calculations. This facility enables you to run different
simulations without physically deleting the information.
8.5.8
The Reporting Schedule
The reporting schedule defined the type of prediction to be performed, the start and end of
prediction and the reporting frequency.
Figure 8.46:
Production Prediction Reporting Schedule
Input Fields
Reporting Frequency
This parameter defines when the prediction result are displayed.
•
Automatic:
The programme displays a calculation every 90 days.
• User List:
The user can specify a list of up to 60 dates in the table provided.
• User Defined:
The user can defined any date increment in days, weeks, months or years in
the adjacent fields.
Keep History
This button is only displayed for a prediction setup where the first part is
actually running in history simulation mode before changing to prediction
mode. If you select this option then the calculations during the history
simulation will be displayed in the results.
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Section III
8.5.9
Running a Prediction
You will not be able to run a prediction until all the necessary data has been input. To run
a prediction, choose Production PredictionRun Prediction. The following dialog box is
displayed:
Figure 8.47:
Production Prediction Calculation
On entering this dialog, the results of the last prediction will be displayed. The scroll bars
to the bottom and right of the dialog box allow you to browse through the calculations.
This dialog can also be used to display other results. Each set of results is stored in a
stream. There are always three streams present by default:- Production history
- The last history simulation
- The last production prediction
Copies of the current production prediction calculations can be made using the Save
button. This will create a new stream.
To change the stream displayed, change the selection in the stream combo-box at the top
left of the dialog.
For single tank cases, each stream corresponds to the one and only tank.
For multi-tank systems, the list of streams is more complex. Within each stream there are
additional items called sheets. Each sheet corresponds to a tank or transmissibility. You
may also select a sheet to display in the streams combo-box. The results displayed if you
select the stream (rather than one of its sheets) are the consolidated results i.e. the
cumulative results from all the tanks.
Rates are reported in three ways in the prediction:-
•
Cumulative rates : This is the total rate produced up to the time at which the rate
is reported.
•
Average rate : This is the average rate over the time period from the last
reported time and the time at which the average rate is reported. e.g. if reported
time steps are every year then an average rate reported at 01/01/1985 is the
average rate over the time period from 01/01/1984 to 01/01/1985.
Petroleum Experts
Chapter 8 - The Material Balance Tool
•
8-93
Rate : This is an instantaneous rate at the time reported.
Note that if a well has a non-zero downtime defined in the well schedule then cumulative
and average rates will include the downtime factor but instantaneous rates will not have
the factor included.
Command Buttons
Layout
Allows you to display a selection of the variables you are only
interested in few of the calculation results. These column selections
are also used by the reporting facility.
Save
Use this button to save the current prediction results in a new stream.
See 8.5.9.1 below for more details.
Calc
Click this button to start a new prediction. A small progress window
with an Abort button will appear in the top right hand corner of your
screen. Press the Abort button at any time to stop the calculation.
Report
Allows reporting of the currently displayed stream/sheet to a file,
clipboard or printer.
Plot
Displays a plot of up to two variables from one or more streams or
sheets. Refer to section 8.5.9.2 for information on the plot.
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Section III
8.5.9.1 Saving Prediction Results
At the conclusion of a prediction run, you may click Save to save the current run in
memory for comparison with other calculations. The following screen will be presented:
Figure 8.48:
Production Prediction Save Calculation Stream
Data Stream
Displays a list of the saved data streams. By default you will normally get the three data
streams:History (production history entered in the tank data)
Simulation (production history simulation)
Prediction (production prediction)
It also displays any data streams that have been saved (see Add below)
Note that you can change the name of any of the streams (apart from the default streams)
simply by clicking on the name and editing the name.
Description
The program automatically provides a default description name. Enter a new meaningful
description for this prediction/simulation run.
Nb Points
Displays the number of calculated points for the prediction/simulation to be saved.
Command Buttons
Add
Creates a new stream which is a copy of the current prediction stream. The
stream is given a default name which you may change.
Replace This can be used to replace an existing stream. Select an existing stream
(not one of default ones) and click Replace. The selected stream will be
replaced by a copy of the current prediction stream. The stream is given a
default name which you may change.
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Remove Deletes the selected stream set from the list. You will be prompted to
confirm the deletion.
Click Done to implement the stream changes. Click Cancel to exit the screen and ignore
the changes.
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Section III
8.5.9.2 Plotting a Production Prediction
To access the prediction plotting facility, click Plot.
appears:
A screen similar to the following
Figure 8.49:
Production Prediction – Plot
screen
To change the variables plotted on the axes, click the Variable plot menu option. The
following dialog box appears:
Figure 8.50:
Production Prediction – Plot
Variable Selection
This dialog box allows you to choose the X and Y variables to plot. Two variables can be
selected from the left list column (Y) and one from the right list column (X).
To select a variable item, simply click the variable name, or use the ↑ and ↓ directional
arrow, and use the space bar to select or de-select a variable item. The program will not
allow more than two variables to be selected from the Y axis at one time.
➲
If you have already selected 2 variables for the Y axis and want to change one of
them, first de-select the unwanted variable, and then choose the new plot
variable.
This option allows the user to select the data streams/sheets to be displayed, allowing the
comparison of the simulation and the prediction on the same plot. To select a data stream
or sheet, click on the name of the stream/sheet. The stream/sheet can be unselected by
clicking again on the same name.
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8.5.10 Displaying the Tank Results
To display the tank results, choose Production PredictionTank Results.
This dialog is exactly the same as the Run Prediction dialog described above except that
the Calc and Save buttons are not available.
8.5.11 Displaying the Well Results
To display the results of each well on the last prediction run, choose Production Prediction
Well Results. The following dialog box is displayed:
Figure 8.51:
Production Prediction Well Results
Select the well to be displayed from the Stream combo-box.
If a well has more than one layer (i.e. connection to a tank), then the different layers will be
shown as sheets. In this case, if the stream (rather than one of the sheets) is selected, the
consolidate well results will be displayed i.e. the cumulative results of all layers in that well.
The Analysis button can be used to view the well performance for the selected row in the
well results. It will extract all the relevant data from the well results required for the Well
Performance Test and display a dialog to allow calculation and plotting of the IPR/VLP and
the operating point. This is the same dialog as can be viewed from the well definition
dialog – see section 8.5.6 above. If compositional tracking is also selected, this button can
also be used to view the details of the composition of the well for the selected row.
In the Status column, the program shows any special conditions for that well. These may
be :
• Abd CGR : Abandonment on CGR constraint,
• Abd Gas
: Abandonment on Gas saturation constraint,
• Abd GOR : Abandonment on GOR constraint,
• Abd Wat
: Abandonment on Water saturation constraint,
• Abd WCT : Abandonment on WCT constraint,
• Abd WGR : Abandonment on WGR constraint,
• Abd WOR : Abandonment on WOR constraint,
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Section III
• End Date : Automatic Well shut-down according to well schedule,
• Gas Brk
: Gas breakthrough.
• Gas Levl
: Abandonment on Gas Contact depth,
• Man Gmax : Rate reduced because of Gas Rate constraint,
• Man Pmax : Rate reduced because of Manifold Maximum pressure,
• Man Pmin : Abandonment because of Manifold Minimum pressure,
• Man Qmax : Rate reduced because of Manifold Maximum rate,
• Man Qmin : Abandonment because of Manifold Minimum rate,
• Max DwDn : Rate reduced because of Maximum Drawdown on the formation,
• Max FBHP : Rate reduced because of Maximum Flowing Bottom Hole Pressure,
• Max Rate : Rate reduced because of Maximum Well Rate,
• Man Wmax : Rate reduced because of Water Rate constraint,
• Min FBHP : Abandonment on Minimum Flowing Bottom Hole Pressure,
• Min Rate
: Abandonment on Minimum Well Rate,
• Neg TPC : The IPR intersects the TPC on the negative slope of the TPC,
• No OptGl : Optimum GLR could not be provided a Gas Lifted Well because of
a constraint on the maximum gas lift gas available,
• No Solut
: No IPR / TPC intersection,
• Out TPC
: Program working outside of the TPC’s generated range,
• Wat Brk
: Water breakthrough.
• Wat Levl
: Abandonment on Water Contact depth.
Command Buttons
Layout
Allows you to display a selection of the variables you are only
interested in few of the calculation results. These column selections
are also used by the reporting facility.
Report
Allows reporting of the currently displayed stream/sheet to a file,
clipboard or printer.
Plot
Displays a plot of up to two variables from one or more streams or
sheets.
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Chapter 8 - The Material Balance Tool
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8.6 Compositional Tracking
The material balance tool allows compositional tracking in both history simulation and
production prediction.
8.6.1 Input Data
To use compositional tracking the following input data must be entered.:-
•
•
•
•
•
•
Select the Options menu and select the Yes option in the Compositional
Tracking combo box.
Next enter the composition of the tanks at the start of the production history (or at
the start of the prediction if there is no production history). Select the PVT menu
and Oil Composition and Gas Composition.
You must enter the composition of the free oil and the composition of the free gas
at this time. If you are using a gas or condensate system then there is no free oil in
the tank - in this case you do not need to enter the oil composition. Conversely, if
you are using an oil system above the bubble point there is no free gas - in this
case you do not need to enter the gas composition. If you have a gas cap and do
not enter a gas composition, the program will use the oil composition for the
gas cap and thus calculate the wrong results. Note that the same input
composition is used for all tanks in a multi-tank system.
If you have entered a gas and oil composition, they must have the same number of
components and the components must have the same names in the same order.
If you have gas injection, gas recycling or gas voidage replacement then you must
also enter the composition of the gas that is injected into the tank. Select the PVT
menu and Gas Injection Composition.
If you enter a gas injection composition, then it does not need to have the same list
of components as any entered oil or gas composition. However the component list
in the gas injection composition must be a subset of the list of components in any
entered oil or gas composition.
The input data for history simulation or production prediction must also be entered
as normal.
8.6.2 Operation
If all this input data has been successfully entered, Mbal is ready to do compositional
tracking.
If you now do a simulation or a production prediction as normal it will calculate the
composition of the free oil, the free gas and the combined composition (of the free oil and
gas) in each tank at each time step.
To view the tank results for the history simulation, select the History Matching-Run
Simulation menu item. The mole fraction of each component is displayed as an extra
column to the far right or the results table. For more detailed results, click on the analysis
button for a particular row - you will be able to view the free oil composition, free gas
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Section III
composition and total composition as well as generate fluid properties and plot the phase
envelope.
The tank results for a production prediction are in the same form but you must access the
Production Prediction-Run Prediction menu item.
If you have performed a production prediction with prediction wells then Mbal will also
calculate the compositions from each layer and also the combined well compositions. To
view the well/layer results, select the Production Prediction-Well Results menu item.
The results are accessed as for the tank results.
8.6.3 What is MBAL Calculating?
The first important thing to note is that this calculation is a post processor. The standard
simulation/prediction results such as pressure, rates, sauturations will be exactly the same
whether compositional tracking is on or off. This is because MBal does not use the
composition to calculate the required fluid properties at each time step - it uses the
standard black oil models.
So what does Mbal actually calculate?
•
•
•
•
•
At the start of the time step, MBal calculates the well and layer compositions using
the well and layer rates plus the composition in the tank at that time.
MBal then calculates the pressure and the new volumes at the end of the time step
as normal.
The composition at the start of the time step is then flashed to the new pressure at
the end of the time step.
Using the new volumes of oil and gas at the end of the time step and the new oil
and gas composition, MBal can calculate a new total composition.
These new compositions are then used as input to the next time step and so on...
Petroleum Experts
Monte-Carlo Technique
Programme Functions
The Monte-Carlo technique is used to evaluate the hydrocarbons in place. Each of the
parameters involved in the calculation of reserves, basically the PVT properties and the
pore volume, are represented by statistical distributions.
Depending on the number of cases (NC) chosen by the user, the program generates a
series of NC values of equal probability for each of the parameters used in the
hydrocarbons in place calculation. The NC values of each parameter are then crossmultiplied creating a distribution of values for the hydrocarbons in place. The results
are presented in the form of a histogram.
Technical Background
The program supports five types of statistical distributions:
In the definitions below f represents the distribution relative frequency and P the
distribution cumulative probability.
•
Fixed Value :
Value = Constant
•
Uniform Distribution :
This distribution is defined by a minimum (Min) and maximum (Max) value with
an equal probability for all values between these 2 extremes.
Value = Min + (Min - Max) *Probability
Figure 9.1:
Monte-Carlo Technique
Uniform Distribution
Chapter 9 - Monte-Carlo Technique
9-2
Section III
•
Triangular Distribution :
This distribution is defined by a minimum, maximum and mode value with:
P mod e = (Mode − Min) (Max − Min)
At value Mode :
If P < Pmode :
If P > Pmode :
P
Value = Min + (Mode − Min) *
P mod e
1− P
Value = Max − (Max − Mode) *
1 − P mod e
Figure 9.2:
Monte-Carlo Technique
Triangular Distribution
•
Normal Distribution :
This distribution is defined by an average (Avg) and a standard deviation (Std)
with:
Value = Avg + Std *
(
Ln(1 p2)
)
Figure 9.3:
Monte-Carlo Technique
Normal Distribution
•
Log Normal Distribution :
This distribution is defined by an average (Avg) and a standard deviation (Std)
with:
Value

Std 
= exp(log( Avg )) + log 1 +
*
Avg 

(
Ln(1 p2)
)
Figure 9.4:
Monte-Carlo Technique
Log Normal Distribution
Petroleum Experts
Chapter 9 - Monte-Carlo Technique
9-3
9.1 Tool Options
On selecting Monte-Carlo as the analysis tool in the Tool menu, go to the Options menu
to define the primary fluid of the reservoir. This section describes the 'Tool Options'
section of the System Options dialogue box.
Refer to Chapter 6 of this guide for more information on the User Information and User
Comments sections.
Figure 9.5:
Monte-Carlo Tool Tool Options
To select an option, click the arrow to the right of the field to display the current
choices. To move to the next entry field, click the field to highlight the entry, or use the
TAB button.
Input Fields
Reservoir Fluid
• Oil
This option uses traditional black oil models. Four correlations are provided. The
parameters for these correlations can be changed to match real data using a
non-linear regression.
• Gas
(Dry and Wet Gas)
Wet gas is handled under the assumption that condensation occurs at the
separator. The liquid is put back into the gas as an equivalent gas quantity. The
pressure drop is therefore calculated on the basis of a single phase gas, unless
water is present.
• Retrograde Condensate
uses the Retrograde Condensate Black Oil model. The regression allows
you to match your PVT data to real data. These models take into account liquid
dropout at different pressures and temperatures.
MBAL
Working with the tool
Before you begin working with the Monte-Carlo analysis tool,
•
April 2001
After making your entries in the Options menu, proceed to the Pvt menu to
enter the PVT properties of the fluid in place. Refer to Chapter 7 for
information on the PVT.
Material Balance Program Version 6
9-4
Section III
•
Next choose Distributions to enter the reservoir parameters.
9.2 Distributions
Figure 9.6:
Monte-Carlo Technique
Distributions
Input Fields
Number of Cases
Defines the number of segments of equal probability the distribution will
be divided into.
Histogram Steps
Defines the number of steps that will be plotted on the histogram.
Temperature
Defines the reservoir temperature.
Pressure
Defines the reservoir initial pressure.
Method
The pore volume can be calculated using:
• Bulk Volume * N/G ratio
• Area * Net Thickness
Distribution Type
For each reservoir parameter listed (Area → Gas Gravity), select the
appropriate distribution type from the list box available for each field entry,
and enter the values required.
When all the necessary parameters have be entered, click Calc to enter the calculation
screen. The following dialogue box is displayed :
Petroleum Experts
Chapter 9 - Monte-Carlo Technique
9-5
Figure 9.7:
Monte-Carlo Technique
Calculations
This calculation dialogue box displays the results of the previous calculation. Click the
Calc command to start a new calculation. The new distribution results are displayed
when the calculation finishes.
To view the results of the 10%, 50% and 90% probabilities, click the Result command.
the following dialogue box is displayed
Figure 9.8:
Monte-Carlo Technique
Results summary
To view the calculations graphically, click the Plot command.
A screen similar to the following appears:
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Material Balance Program Version 6
9-6
Section III
Figure 9.9:
Monte-Carlo Technique
Plot screen
For more information on the plot menu commands, refer to Chapter 5.
Petroleum Experts
Decline Curve Analysis
Programme Functions
This tool analyses the decline of production of a well or reservoir versus time. It uses
the hyperbolic decline curves described by Fetkovich based on the equation :
q
=
qi
(1+bi *a *∆t )
−
1
a
¦
where:
q is the production rate,
qi is the initial production rate,
a is the hyperbolic decline exponent,
bi is the initial decline rate,
t is the time.
By integrating equation ¦ , the cumulative production can be represented by:
for
a≠1
 1

1 qi 
 1− 
P=
 (1 + bi * a * ∆t ) a  − 1
a − 1 bi 

for
a=1
P=
qi
* ln(1 + bi * ∆t )
bi
The program also supports production rate 'breaks' or discontinuities. These breaks
can be attributed to well stimulation, change of completion, etc.
10.1 Tool Options
The Decline Curve analysis tool can be used for Production History Matching and/or
Production Prediction. For Production History Matching, the program uses a non-linear
regression to determine the parameters of the decline.
Once you choose Decline Curve as the analysis tool in the Tool menu, go the Options
menu to define the primary fluid of the reservoir. This section describes the 'Tool
Options' section of the System Options dialogue box. For information on the User
Information and User Comments sections, refer to Chapter 6 of this guide.
Figure 10.1:
Decline Curve Analysis Tool Options
Chapter 10 - Decline Curve Analysis
10-2
Section III
To select an option, click the arrow to the right of the field to display the current
choices. To move to the next entry field, click the field to highlight the entry, or use the
TAB button.
Input Fields
Reservoir Fluid
Choose from oil, gas and retrograde condensate. However, the choice only
effects the input and output units of the rates as the theory does not take any
fluid properties into account.
Production History
- By Tank
This option requires you enter the production history for a single well or
the reservoir as a whole.
- By Well
The well by well option requires you to enter the production history for
each well or group of wells. You will then be allowed to match the
production of individual wells and select the list of wells to be included in
the production prediction computation.
•
➲
Next choose Input Production History to enter the production history.
Please note that the remainder of this chapter describes the features of the
program using the Well by Well mode. Some screens will differ slightly if the
Reservoir mode is used, but are usually simpler.
10.2 Production History
This screen is used to enter the well production history, along with the time or date of
the eventual production rate breaks. The following dialog box appears:
Figure 10.2:
Decline Curve Analysis
Production History
Petroleum Experts
Chapter 10 - Decline Curve Analysis
10-3
Input Fields
Well List
A list of all the wells created in this data set. This list box can be used to scan
the well models entered, by clicking on the name of the well you wish to
display. This list box is only displayed if you have selected to enter the
production history By Well in the options dialog.
The well name is usually preceded by an marker indicating the status of the
well:
-
indicates that the well data is valid. This well can be used in the
production prediction calculation.
-
No marker and the well name appears in red. The well data is
incomplete or invalid. This well cannot be used in the production
prediction calculation.
Well Name
A string of up to 12 characters containing the well, tank or reservoir name. This
name is used by the plots and reports.
Decline Type
Select the type of decline curve analysis; hyperbolic, harmonic or
exponential.
Description (optional)
A brief description of the well, tank or reservoir.
Production Start
This field is used as a date origin for plot displays and reporting purposes only.
It is used to produce plots and reports with date references, when the production
history is entered in days or years. When the production history is entered by
date, the reports and plots can be generated in days or years.
Abandonment Rate (optional)
This field is defines the minimum production rate for this well.
Decline Rates
Use this table to enter a list of decline periods (initial rate + decline rate) versus
time. At least one decline period rate must be entered. Several decline periods
can be entered if there is a discontinuity in the decline rate of the production of
the well. This can be due to a well stimulation, a change of completion,
extended shut-down period, etc. Note that the exponent is the same for all the
decline period. Only the initial rate and the decline rate are changing.
This table can be filled in by using the Match option (see Matching the Decline
Curve section that follows). Records can be switched 'Off' or 'On' by depressing
the buttons to the left of the column entry fields. When a record is switched 'Off',
it is not taken into account in the calculations.
Production History (optional)
April 2001
Material Balance Program Version 6
10-4
Section III
Use this table to enter the production rate history. Records are automatically
sorted in ascending order by time, or date.
To view more records, use the scroll bar to the right of the columns. To delete a
record, simply blank out all the fields in the corresponding row. To add or insert
a new record, just enter the records at the end of the list you have already
created, and the program will automatically sort the records in ascending order.
Records can be switched 'Off' or 'On' by depressing the buttons to the left of the
column entry fields. When a record is switched 'Off', it is not taken into account
in the calculations.
The production history is used to automatically generate the exponent, initial
rates and decline rates. This can be done by clicking the Match button (see
Matching the Decline Curve section that follows).
Enter the required information, and press Done to confirm the input data and exit the
screen. If you want to check the quality and validity of the data, click the Plot command
button.
Command Buttons :
Plot
Displays the production history profile versus time.
Reset
Initialises the current tank/well data.
Match
Allows the calculation of the exponent, initial rates and decline rates
from the production data.
Import
Reads a data file generated by other systems which contains
production history data. (see Chapter 4)
Add
Creates a new well. For By Well input only.
Del
Removes the well currently selected for the well list. The data
contained in the well is lost. For By Well input only.
Petroleum Experts
Chapter 10 - Decline Curve Analysis
10-5
10.3 Matching the Decline Curve
To access the history matching screen, click in the Match from the production history
screen A screen plot similar to the following plot appears :
Figure 10.3
Decline Curve Analysis
History Matching plot
On first entry into this screen, only the matching points are displayed.
Choose Regress to start the non-linear regression and find the best fit. The Decline
Curve parameters corresponding to the best fit found by the regression are displayed in
the legend box the right of the plot.
Changing the weighting of history points in the regression
Each data point can be given a different weighting in the Regression. Important and
trustworthy data points can be set to HIGH to force the regression to go through these
points. Secondary or doubtful data points can be set to LOW or switched OFF
completely.
Changing Single Points:
Figure 10.4:
Decline Curve Analysis
- Set Match Point Status
(Single Point)
April 2001
Material Balance Program Version 6
10-6
Section III
Using the LEFT mouse button, double-click the history point to be changed. The above
dialogue box appears, displaying the point number selected.
Choose as required, the point weighting (High / Medium / Low) and/or status (Off / On).
Points that are switched off will not be taken into account in the regression. Checking
the Insert Rate Break option creates a new entry in the decline rate table, i.e. indicates
to the program the occurrence of a discontinuity in the rate decline.
If a rate break has already been inserted at that point, the following screen is displayed:
Figure 10.5:
Decline Curve Analysis
- Remove rate break
(Single Point)
Checking the Remove Rate Break removes the corresponding entry from the decline
rate table.
Click Done to confirm the changes.
Changing Multiple Points :
Figure 10.6:
Decline Curve Analysis Set Match Point Status
(Multiple Point)
Using the RIGHT mouse button and dragging the mouse, draw a dotted rectangle over
the points you want to modify. (This click and drag operation is identical to the
operation used to re-size plot displays, but uses the right mouse button.) When you
release the mouse button, a dialogue box similar to the above will appear, displaying
the number of points selected.
All the history points included in the 'drawn' box will be affected by the selections you
are about to make. Choose the points' weighting (High / Medium / Low) and/or status
(Off / On) as desired. Click Done to confirm the changes. If you have no right mouse
Petroleum Experts
Chapter 10 - Decline Curve Analysis
10-7
button, the button selection can still be performed by using the left mouse button and
holding the shift key down while you click and drag.
➲
Do not forget to choose Regress again to start a new regression with the new
values.
Menu Commands:
Axis
Allows you to select different types of scales for the X and Y axes.
You can also choose to display the estimated cumulative production
based on the last regression parameters.
Prior
Plots the production data of the previous well in the well list of the
production screen above.
Next
Plots the production data of the next well in the well list of the
production screen above.
Regress
Starts the non-linear regression and finds the best fit. The Decline
Curve parameters corresponding to the best fit found by the
regression are displayed in the legend box the right of the plot.
Decline
Type
Select the type of decline curve analysis; hyperbolic, harmonic or
exponential.
10.4 Prediction Set-up
This option is used to enter the production prediction parameters To access the
prediction parameters screen, choose Production Prediction - Prediction Set-up. The
following dialogue box appears:
Figure 10.7:
Decline Curve Analysis Prediction Set-up
Input Fields
Start of Prediction
This field defines the start date of the prediction.
April 2001
Material Balance Program Version 6
10-8
Section III
Prediction end
This parameter defines when the program will stop the prediction.
Abandonment rate (optional)
This field defines the minimum production rate for the prediction.
Wells to include (only displayed if By Well selected in the Options dialogue)
Select the wells to be included in the prediction. Only valid wells are presented
in this list.
10.5 Reporting Schedule
The reporting schedule defines the type of prediction to be performed, the start and
end of prediction and the reporting frequency.
Figure 10.8:
Decline Curve Analysis Reporting Schedule
Input Fields
Reporting Frequency
This parameter defines when the prediction results are displayed.
• Automatic:
The program displays a calculation every 90 days.
• User List:
The user can specify a list of up to 60 dates in the table provided.
• User Defined:
The user can define any date incremented in days, weeks, months or
years in the adjacent fields.
Petroleum Experts
Chapter 10 - Decline Curve Analysis
10-9
Enter the required information, and press Done to confirm the input data and exit the
screen.
10.6 Running a Production Prediction
To run a prediction, choose Production PredictionCalculation. The following dialogue
box is displayed:
Figure 10.9:
Decline Curve Analysis Production Prediction Calculation
This screen shows the results of the last prediction. The scroll bars to the bottom and
right of the dialogue box allow you to browse through the calculations of the last
prediction run.
To start a new prediction, click Calc. To abort the calculations at any stage, press the
Abort command button.
The Layout button allows you to display a selection of variables if you are only
interested in a few of the calculation results. This option may also be used for printing
reports.
Plotting a Production Prediction:
To plot the results of a prediction run, choose Production PredictionPlot. This plot
allows you to select the variables to display.
April 2001
Material Balance Program Version 6
1D Model
11.1
Programme Functions:
This tool allows the study of the displacement of oil by water or gas, using the fractional
flow and Buckley-Leverett equations.
The model does not presuppose any
displacement theory.
Figure 11.1: 1D Model Theory Diagram
The model assumes the following:
•
The reservoir is a rectangular box, with an injector well at one end and a
producer at the other.
•
The production and injection wells are considered to be perforated across
the entire formation thickness.
•
The injection rate is constant.
•
The fluids are immiscible.
•
The displacement is considered as incompressible.
•
The saturation distribution is uniform across the width of the reservoir.
•
Linear flow lines are assumed, even in the vicinity of the wells.
•
Capillary pressures are neglected.
11.2
Technical Background:
The reservoir is a rectangular box, with an injector well at one end and a producer at
the other. The box is divided into cells for which average water/gas and oil saturations
are monitored. A time step is computed based on the injection rate and the overall size
of the reservoir, so as not to produce brusque changes in the cells' saturations. At
each time step, the program calculates the production from cell to cell. The calculation
is performed from the producer well to the injector.
At each time step and for each cell, the program calculates:
•
•
•
•
The water/gas and oil relative permeabilities based on the cell saturations.
The fractional flow of each fluid based on their relative permeabilities.
The cell productions into the next cell based on the fractional flows.
The new cell saturations from the productions.
Chapter 11
1D Model
11-2
Section III
Simultaneous Flow
In the case of displacement of oil by water, the one dimensional equations for
simultaneous flow of oil and water can be expressed as:-
qo =
ρog sin θ 
kkroA  δPo
−


× 10e6 
.
µo  δx 10133
qw =
ρwg sin θ 
kkrwA  δPw
−


µw  δx 10133
.
× 10e6 
and
where:
q = rate
ρ = density
k = permeability
A = cross section area
µ = viscosity
P = pressure
g = acceleration of gravity.
Fractional Flow
The Fractional Flow can then be expressed as:
∆ρg sin θ 
kkroA  δPc
−
1+


× 10e6 
qtµo  δx 10133
.
qw
fw =
=
µw kro
qw + qo
1+
×
krw µo
which, neglecting the capillary pressure gradient with respect to x, gives:
kkroA
∆ρg sin θ
1−
×
qtµo 1. 0133 × 10e6
.
fw =
µw kro
1+
×
krw µo
For a displacement in an horizontal reservoir the equation is reduced to
M
1
fw =
=
µw kro 1 + M
1+
×
krw µo
µo krw
×
.
with the end point mobility factor defined as M =
kro µw
Petroleum Experts
Chapter 11 – 1D Model 11-3
11.3 Tool Options
On selecting 1D Model as the analysis tool in the Tool menu, go to the Options menu to
define the primary fluid of the reservoir. This section describes the 'Tool Options'
section of the System Options dialogue box.
Refer to Chapter 6 of this guide for more information on the User Information and User
Comments sections.
Figure 11.2:
1D Model -Tool Options
Input Fields
Reservoir Fluid
The only fluid selection for this tool is oil.
Supply the header information and any comments about this analysis in the appropriate
boxes. Click Done to accept the choices and return to the main menu.
Two main menu options then become available:
April 2001
•
Input to enter the reservoir, fluids and injection parameters,
•
Calculation to run a simulation and produce result reports and plots.
Material Balance Program Version 6
11-4
Section III
11.4
Reservoir and Fluids Properties
To access the reservoir, injection and fluids properties dialog box, choose Input Reservoir Parameters or press ALT - R. A screen similar to the following appears.
Figure 11.3:
1D Model Reservoir and Fluids Parameters
Input Fields
Injection Fluid
Choose between water or gas.
Injection Rate
Defines the injection rate of the injection fluid.
Start of Injection
Used as the origin of the date system.
Oil Density
Density of the oil at reservoir conditions.
Oil Viscosity
Viscosity of the oil at reservoir conditions.
Oil FVF
Oil Formation Volume Factor at reservoir conditions.
Solution GOR
For gas injection only. Used to calculate the total gas production (free +
solution).
Water/Gas Density
Density of the injected fluid at reservoir conditions.
Water/Gas Viscosity
Viscosity of the injected fluid at reservoir conditions.
Water/Gas FVF
Injected fluid Formation Volume Factor at reservoir conditions.
Petroleum Experts
Chapter 11 – 1D Model 11-5
Figure 11.4: Theoretical 1D Model Reservoir
Reservoir Length
Refer to diagram 11.4. as a guide for entering the reservoir parameters.
Reservoir Width
Refer to diagram 11.4. as a guide for entering the reservoir parameters.
Reservoir Height
Refer to diagram 11.4. as a guide for entering the reservoir parameters.
Oil/Water or Gas/Oil Contact
The vertical distance from the top of the reservoir at the producing end to
the fluid interface.
Dip Angle
Refer to diagram 11.4. as a guide for entering the reservoir parameters.
Permeability
The average absolute permeability of the reservoir.
Porosity
The average reservoir porosity.
Cut-off Water Cut or GOR
Value of the Water Cut (for water injection) or GOR (for gas injection) at
which the program will end the simulation run.
Number of cells
Define the number of cells the block will be divided into for the simulation
run (maximum 500). Choose a higher value if the injected volume is
important.
Enter the correct information appropriate boxes. Click Done to accept and return to the
main menu.
April 2001
Material Balance Program Version 6
11-6
Section III
11.5
Relative Permeability
To access the relative permeabilities dialog box, choose Input - Relative Permeabilities
or press ALT - P. A screen similar to the following will appear.
Figure 11.5:
1D Model Relative permeabilities
➲
See Corey Relative Permeability Equations in Appendix C2
Input Fields
Rel Perm From
Select whether the relative permeabilites are to come from
- Corey Functions, or
- User Defined input tables.
Residual Saturations
Defines respectively : - The connate saturation for the water phase,
- The residual saturation of the oil phase for water flooding,
These saturations are used to calculate the amount of oil ‘by-passed’
during a water flooding.
End Points
Defines for each phase the relative permeability at its saturation maximum.
For example for the oil, it corresponds to its relative permeability at So = (1Swc).
Corey Exponents
Defines for each phase the relative permeability at its saturation maximum.
For example for the oil, it corresponds to its relative permeability at So = (1Swc).
Petroleum Experts
Chapter 11 – 1D Model 11-7
Command Buttons:
Reset
Initialises the relative permeability curve
Plot
Displays the relative permeability tables in a graph.
Copy
Copy a relative permeability curve from elsewhere in the system.
Click Done to exit and return to the main menu screen, or Cancel to quit the screen.
Input Fields
Residual Saturations
Defines respectively :
- The connate saturation for the water phase,
- The residual saturation for the oil phase,
- The critical saturation for the gas phase.
End Points
Defines for each phase the relative permeability at its saturation maximum.
For example for the oil, it corresponds to its relative permeability at So = (1Swc).
Corey Exponents
Defines for each phase the relative permeability at its saturation maximum.
For example for the oil, it corresponds to its relative permeability at So = (1Swc).
Enter the relevant information, and click the Plot button to check the quality and validity
of the data.
➲
Please note that relative permeabilities are always represented as functions
of water saturation.
April 2001
Material Balance Program Version 6
11-8
11.6
Section III
Running a Simulation
To run a simulation choose Calculations - Run simulation, or press ALT C R. A screen
similar to the following will appear.
Figure 11.6:
1D Model –Simulation
The display shows most of your input parameters. Click Calculate from the window
menu to start a simulation run.
The program displays the change in the distribution of the injected phase saturation.
Each curve represents a distribution of saturations for a given pore volume injected
(indicated on the plots as PV injected).
The calculation can be stopped at any time by clicking the Abort button. If the
calculations are not stopped, the program ends the simulation at the cut-off value
entered in the 'Reservoir and Fluids Parameters' dialogue box.
The bottom right portion of the screen displays the values of different parameters at
Breakthrough and at the end of the simulation.
Input parameters can be accessed throughout the Input menu option. When changes
to the input parameters are completed, press Calculate to start a new simulation.
Full details of the calculations behind the plot can be viewed by choosing Output Result. They may be printed and plotted differently using any of the options provided.
Petroleum Experts
Chapter 11 – 1D Model 11-9
11.6.1 Plotting a Simulation
To view other calculated parameters, choose Output - Result - Plot. To change the
variables plotted on the axes, click the Variable plot menu option. A dialogue box
appears which allows you to choose the X and Y variables to plot. Two variables can
be selected from the left list column (Y) and one from the right list column (X).
To select a variable item, simply click the variable name, or use the ↑ and ↓ directional
arrow, and use the space bar to select or de-select a variable item. The program will
not allow more than two variables to be selected from the Y axis at one time.
➲
If you have already selected 2 variables for the Y axis and want to change one of
them, first de-select the unwanted variable, and then choose the new plot
variable.
For more information on the plot display menu commands, refer to Chapter 5.
April 2001
Material Balance Program Version 6
Multi Layer Tool
12.1
Programme Functions:
This tool allows the calculation of a set of pseudo-relative permeability tables for a
multi-layered reservoir where the relative permeability curves are available for the
individual layers.
The model assumes the following:
•
There is no crossflow between the individual layers
•
The fluids are immiscible.
•
Capillary pressures are neglected.
12.2
Technical Background
The reservoir is a rectangular box, with water sweeping from one end of the reservoir to
the other. The reservoir is split into a number of rectangular layers. Each layer has its
own porosity, permeability and height. All other properties are common to all the layers.
Each layer also has its own set of relative permeabilities. The purpose of the tool is to
calculate a set of relative permeability tables which represent the behaviour of the
entire reservoir.
The calculation tracks the water front on each layer using the relative velocity
calculated from:'
k i k rwi
vi ∞
φ (1 − S ori − S wci )
Where:i - layer number
ki – permeability
krw’ – end point water relative permeability
Sori – residual oil saturation
Swci – connate water saturation
Chapter 12
Multi-Layer Tool
12-2
Section III
An artificial simulation time frame is set up to allow all of the layers to fill completely
with water. At each time step the program calculates:•
•
•
•
The water front position from the velocity
The water saturation of each layer
The relative permeability of each layer from the layer water saturation
The water saturation and relative permeability of the complete reservoir by
averaging the layers:-
∑ S φh
∑ φh
∑ k kh
=
∑ kh
∑ k kh
=
∑ kh
S wT =
T
K rw
K roT
w
rw
ro
This algorithm will ensure that a thin, high permeability layer will cause the water
relative permeability to increase markedly at small average saturations.
Once the pseudo relative permeabilities have been calculated, they may be used as
input to either the 1-D Model or the Material balance tool.
Petroleum Experts
Chapter 12 Multi-Layer Tool
12.3
12-3
Tool Options
On selecting Multi Layer as the analysis tool in the Tool menu, go to the Options menu
to define the primary fluid of the reservoir. This section describes the Tool Options
section of the System Options dialogue box.
Refer to Chapter 6 of this guide for more information on the User Information and User
Comments sections.
Figure 12.1:
Multi-layer -Tool Options
To select an option, click the arrow to the right of the field to display the current
choices. To move to the next entry field, click the field to highlight the entry, or use the
TAB button.
Input Fields
Reservoir Fluid
This tool currently handles water flooding into an oil reservoir.
Supply the header information and any comments about this analysis in the appropriate
boxes. Click Done to accept the choices and return to the main menu.
Two main menu options then become available :
•
Input to enter the reservoir, fluids and injection parameters,
•
Calculation to run a simulation and produce result reports and plots.
April 2001
Material Balance Program Version 6
12-4
Section III
12.4
Layer Properties
To access the layer properties dialog box, choose Input-Layer Properties. A screen
similar to the following appears.
Figure 12.2:
Multi-layer Layer Properties
Input Fields
Thickness
Thickness of the layer.
Porosity
Porosity of the layer.
Permeability
Absolute permeability of the layer.
Enter the information for each layer in the reservoir. Then click on the corresponding
Rel Perm button to enter the relative permeability curve for each layer. A tick will
appear next to the Rel Perm button to indicate that a valid relative permeability curve
has been entered.
Click the Reset button to delete all the layers and their relative permeability curves.
Click Done to accept and return to the main menu.
Petroleum Experts
Chapter 12 Multi-Layer Tool
12-5
12.4.1 Relative Permeability
To access the relative permeabilities dialog box for a particular layer, click on the Rel
Perm button. A screen similar to the following will appear.
Figure 12.3:
Multi-Layer Relative permeabilities
➲
See Corey Relative Permeability Equations in Appendix C2
Input Fields
Rel Perm From
Select whether the relative permeabilites are to come from:- Corey Functions, or
- User Defined input tables.
Residual Saturations
Defines respectively:- The connate saturation for the water phase,
- The residual saturation of the oil phase for water flooding,
These saturations are used to calculate the amount of oil ‘by-passed’ during a
water flooding.
End Points
Defines for each phase the relative permeability at its saturation maximum. For
example for the oil, it corresponds to its relative permeability at So = (1-Swc).
Corey Exponents
Defines for each phase the relative permeability at its saturation maximum. For
example for the oil, it corresponds to its relative permeability at So = (1-Swc).
April 2001
Material Balance Program Version 6
12-6
Section III
Command Buttons:
Reset
Reset the relative permeability curve
Plot
Displays the relative permeability tables in a graph.
Copy
Copy a relative permeability curve from another location in the
program e.g. another layer.
Prev
Edit the rel perms for the previous layer in the table.
Next
Edit the rel perms for the next layer in the table.
Click Done to exit and return to the main menu screen, or Cancel to quit the screen.
Enter the relevant information, and click the Plot button to check the quality and validity
of the data.
➲
Please note that relative permeabilities are always represented as functions
of water saturation.
12.5 Running a Calculation
To run a calculation choose Calculations
Run Calculation. A screen similar to the
following will appear.
Figure 12.4:
Multi-layer – Calculation
Click the Calculate button to start a simulation run. The calculation can be stopped at
any time by clicking the Abort button. At the end of the calculation, the calculated
pseudo relative permeability curve is displayed.
Petroleum Experts
Chapter 12 Multi-Layer Tool
12-7
Click on the Plot button to view the relative permeability curve. For more information on
the plot display menu commands, refer to Chapter 5.
The pseudo relative permeability curve that is calculated here can be used by the 1-D
Model and Material Balance Tool. To do so:-
Calculate the pseudo relative permeability curve as described above.
-
Select the other tool that you wish to use - do not select File-New or FileOpen at this point or the table will be lost.
-
In the relative permeability dialog for the other tool, select the Copy button
and the pseudo relative permeability curve should appear in the list labelled
as Multi Layers – Reservoir.
April 2001
Material Balance Program Version 6
Examples
A.1 Water Drive Oil Reservoir
The data file containing this example is OIL_TST.MBI.
This example is designed to show how to find the Oil-in-Place and fit an aquifer model
for a reservoir with a water drive. Operations covered include:
Setting modelling options
Entering PVT properties and performing a correlation match
Entering reservoir and aquifer properties
Entering production history data
Performing a history match
Using regression to improve the match
•
•
•
•
•
•
This example is based on data from Fundamentals of Reservoir Engineering by L.P.
Dake (Elsevier, 1978), Chapter 9.
Setting up the Problem
Begin the session by clearing all previous calculations. Click File - New. Save
changes to your previous work if required. Select Tool - Material Balance, then click
Options from the main menu. Make the following selections:
Reservoir Fluid:Tank Model:PVT Model:Production History:Compositional Tracking:-
Oil
Single Tank
Simple PVT
By Tank
No
Click Done to return to the main menu.
PVT Menu
Click PVT - Fluid Properties and enter the following PVT data:
Formation GOR:Oil Gravity:Gas Gravity:Water Salinity:Mole % H2S:Mole % CO2
Mole % N2
650 scf/STB
40 API
0.6 s.g.
140000
0
0
0
Appendix A - Examples
A-2
Appendices
Make the following selections:
Separator
Correlations - Pb, Rs, Bo
Oil Viscosity
Single Stage
Glaso
Beal, et al
We will now match the correlations to lab PVT data. Click the Match button and enter
the following PVT match data for a temperature of 160 degrees F and a bubble point of
2725.3 psig:
Pressure
psig
Gas/Oil
Ratio
scf/STB
Oil FVF
RB/STB
2725.3
1934.0
1425.0
650
471
364
1.404
1.316
1.27
Oil Viscosity
cp
Once this has been entered, click Match to display the matching screen. For
parameters, select Match All and the program will attempt to match on bubble point,
GOR and FVF. To regress on all correlations, check Match all, then click the
Calculate button to perform the regression.
Inspect the results by clicking the Match Param button to display this screen:
Choose the correlation which needs the smallest change in matching parameters from
the default values (i.e. 1.0 for parameter 1 and 0.0 for parameter 2). This assumes that
the correlation also matches the input data reasonably well. Glaso appears to be the
best correlation for Pb and GOR. As no viscosity data was available, no adjustment of
the oil viscosity correlation can be done. Return to the PVT input screen by clicking
Done 3 times.
Petroleum Experts
Appendix A - Examples A-3
To use the matched PVT correlations, ensure that Glaso and Beal et al have been
selected, and that Use Matching has been selected. To view the PVT data, click Calc,
select Automatic option for the data points and enter the following calculation ranges:
From
To
Step
Temperature
degrees F
Pressure
Psig
160
160
1
100
6000
50
Click Calc to display the PVT Calculations results box and then click Calc again to
perform the calculation. Then click Plot to display the matched correlation data
together with the lab PVT data. To display the following graph, select pressure on the
X-axis and GOR on the Y-axis:
Return to the main menu by clicking Finish and Done 3 times. This completes the PVT
input and matching process.
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A-4
Appendices
Reservoir Input
The next task is to set up the reservoir geometry and aquifer model. As we can not be
certain of the value of many of these parameters at this stage, just enter reasonable
estimates. The objective of the history matching stage of the program is to refine these
estimates. To begin the process, choose Input - Tank Data. Click on the Tank
Parameters tab and enter the following data:
Tank Type
Temperature
Initial Pressure
Porosity
Connate Water Saturation
Water Compressibility
Initial Gas Cap
Original Oil in Place
Start of Production
Oil
160 degrees F
2725.3 psig
0.25
0.05
3.0 E-06
0
312 MSTB
12/08/1979
Also, click the Monitor Contacts button ON, the Has Dry Gas Producers button OFF
and the Gas Coning button OFF. The Oil in Place is an estimate based on geophysical
mapping, and will be optimised during the history matching process.
Aquifer Input
Next click on the Water Influx tab and enter the following data:
Model
System
Reservoir Thickness
Reservoir Radius
Outer/Inner Radius Ratio
Encroachment Angle
Aquifer Permeability
Hurst-van Everdingen-Dake
Radial Aquifer
100 ft
9200 ft
1.0
140 degrees
200 millidarcies
The reservoir radius is an estimate based on geophysical mapping, and will be
optimised during the history matching process. The RD value of 1.0 means there is no
aquifer influx for the moment.
Rock Properties
Next click on the Rock Properties tab. Select the User Specified button and enter the
following:Rock Compressibility
4.0e-06
Petroleum Experts
Appendix A - Examples A-5
Pore Volume vs Depth
The reservoir is an anticlinal dome. To more accurately calculate fluid contact
movements, click on the Pore Volume vs Depth tab and enter the following
planimetered data:
Pore
Volume
Fraction
0.0
0.03
0.07
0.15
0.27
0.45
0.7
1.0
Depth
Ft
5000
6000
7000
8000
9000
10000
11000
12000
Click Plot to view the pore volume vs depth relation.
Relative Permeability
Next click on the Relative Permeability tab. First select Corey Functions from the Rel
Perm from list box. Check that No is selected in the Modified list box. Enter the
following data:Water Sweep
Efficiency
Gas Sweep Efficiency
100 percent
100 percent
Residual Saturations
Krw
Kro
Krg
Residual Saturation
End Point
Exponent
0.05
0.15
0
0.4
0.8
0.2774
1.5
2
1.35198
Click Plot to view the relative permeability curves.
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A-6
Appendices
Production History
The next task is to set up the production history. Click on the Production History tab.
Enter the following production data:
Time
d/m/y
Reservoir
Pressure
Psig
Cum Oil
Produced
MMSTB
Cum Gas
Produced
MMscf
11/08/1980
11/08/1981
11/08/1982
12/08/1983
11/08/1984
11/08/1985
11/08/1986
12/08/1987
11/08/1988
11/08/1989
2537.80
2362.54
2210.21
2072.14
1936.26
1841.09
1765.08
1726.8
1678.5
1663.6
8.611
19.151
29.881
40.547
50.023
58.303
65.272
70.217
74.028
76.918
6004.2
15580.4
26833.3
38713.7
51521.5
62343.8
71728.0
78777.1
85463.9
89933.7
Check the data input by clicking on Plot. Click Finish - Done to return to the main
menu. This completes the data entry phase.
History Matching
The purpose of this section is to illustrate a methodology for carrying out the matching
process and compare the results obtained using a number of different methods. Bear
in mind that the set of reservoir data entered in the Input section is used only as the
starting point for the history matching. The values of the parameters will be varied until
a match is obtained.
Initially, we have disallowed aquifer influx by setting Rd = 1.0. This will allow us to
assess if an aquifer is present or not. Click History Matching - All and 4 tiled windows
showing the available methods will be displayed. Display the graphical plot full size by
double clicking on its window title bar. The graphical plots are based on the basic
material balance formula:F = N*Et + We
Where
F = Total Production
We = Water Influx
Et = Total Expansion
N = Original Oil in Place
Select the Campbell method using the Method menu item. This plot displays:(F – We)/Et vs F
Petroleum Experts
Appendix A - Examples A-7
so we would theoretically expect the data to fit to a horizontal line whose intersection
with the Y axis gives the OIP. However we see an increase of energy with time which
can indicate one of two things:1. The tank has a low permeability which means that we are seeing more and
more of the tank energy with time. In this case material balance may have
limited application.
2. An aquifer is present.
The logarithmic shape of the data suggests that a radial aquifer may be the source of
the increasing energy.
First try straightening the data by adding an aquifer to the system. Take a note of the
range of the data on the Y-axis. Click on the Input - Tank Data menu item and select
the Water Influx tab. Enter an Outer/Inner Radius Ratio of 6 and an Aquifer
Permeability of 100 as our first estimates for the aquifer. Click on Done. We are still
nowhere near a straight horizontal line but note that the range of the data on the Y-axis
has significantly decreased which indicates that we our new estimates are going in the
correct direction.
Next select the F/Et vs We/Et method using the Method menu item. We would
theoretically expect the data to fit to a straight line with a unit slope and intersection
with the Y axis giving the OIP. With the current estimates it gives a reasonably straight
line. We could continue to increase the quality of the estimates by manually changing
the values and checking the various graphical plots. However this is a time consuming
process. Therefore we will now try using an automatic regression to fine tune the
results.
To improve the chances of obtaining good results from a regression we need to start
with reasonable estimates. We have already seen that out current estimates give
reasonable graphical plots. In addition we should also check the Wd Function plot.
Minimize the graphical plot so that all four history plots are visible. Double click on the
Wd Function plot. On this plot you can select the Rd value by double-clicking on the
appropriate curve. You should select an Rd value such that most of the data lies on the
infinite acting section of the curve i.e. the sloping part of the curve. In this example the
current selected curve (Rd=6.0) already satisfies this condition.
Minimize the Wd Function plot and double click on the Analytic Method plot. Click on
the Regression menu item. In this calculation, MBal will automatically vary the
selected parameters to obtain the best match to the production history data. Click on
the Regress On tick boxes of the following parameters:•
•
•
•
Oil in Place
Outer/Inner Radius
Encroachment Angle
Aquifer Permeability
Click on the Calc button to start the regression. When the regression has finished, click
on each of the
buttons to copy the best fit column value over to the start column
April 2001
Material Balance Program - Version 6
A-8
Appendices
value – these values will then be written to the tank data. Click Done to return to the
analytic plot.
The final step is to check the quality of the regression results. On the analytic plot
check that the simulated line with Aquifer Influx, matches the production history points.
Minimize the analytic plot and double click on the graphical plot. The F/Et vs We/Et plot
should give a straight line. Select the Method menu item and change to the Campbell
method. The data is unlikely to lie on a horizontal line but note the range of data on the
Y-axis should be small.
Minimize the graphical plot and double click on the energy plot. This plot clearly
indicates that the energy due to the formation compressibility is negligible. Click on the
Finish menu item to return to the main MBal screen.
The next verification is to perform a history simulation. This calculates the tank
pressure from the input tank data, PVT and the production history rates. Select History
Matching – Run Simulation and then click the Calc button to run the history
simulation. Once the calculation has finished, click on the Plot button. From the plot,
click on the Variables menu item to select the variables to plot for comparison. On the
Plot Variables dialog, click on both the history and simulation streams in the left
hand box and click on the Tank Pressure in the middle box (make sure no other
selections are made in the middle box). This will allow you to compare the pressure
from the production history and the calculate pressure.
Finally we will perform a sensitivity run to assess the uniqueness of the results. Click on
History Matching – Sensitivity. This calculation allows us to perform a number of
history simulations over a range of values. Click on the Oil in Place and Outer/Inner
Radius tick boxes. Enter the following data:Variable
Oil in Place
Outer/Inner Radius
Steps
20
20
Minimum
100
2
Maximum
400
12
Click on the Plot button which calculates the values and plots the standard deviation
against the oil in place. Zoom in to the region near the solution of the OIP. We can see
that the minimum standard deviation is achieved around the value that the regression
found for the oil in place. However we can also clearly see that if we deviate from this
value, the standard deviation does not increase very quickly. This unfortunately means
that if there is any error in our production history data this may give a large error in our
results from the regression.
A.2 Forward Prediction
The data file containing this example is FORWARD.MBI.
This example describes the steps required to prepare a production forecast for a field
for which there is no production history. The Oil-in-Place is calculated using the Monte
Carlo method. Well productivity is estimated, a well completion schedule is entered
and MBAL is used to calculate production rates. The reservoir pressure and fluid
contacts are monitored to estimate water cut etc. and externally generated lift curves
are used to ensure the production rate decline models actual conditions.
Petroleum Experts
Appendix A - Examples A-9
The major tasks covered by this example are:
•
•
•
•
Entering the oil PVT properties
Estimating the Oil-in-Place using the Monte-Carlo tool
Setting up the modelling options
Running the production prediction
File Menu
The first step is to clear the program memory of any previous calculations. This is
done by clicking on File - New. The file name at the top of the screen will be reset to
untitled and only the File and Tool menu options will remain.
Tool Menu
We will return to this menu several times to select the correct reservoir engineering tool
required to carry out each phase of the forward performance prediction. Select the
Monte Carlo tool by clicking on Tool and selecting Monte Carlo. The rest of the menu
choices will now be displayed. Note that the dimmed menu items cannot yet be
accessed, as they require more data to be input before they can be activated.
Options Menu
Click on Options from the main menu and select 'Oil' as the reservoir fluid. You may
also enter header and comment data also if you wish. Click the Done button to return
to the main menu.
PVT Menu
Click on PVT - Fluid Properties to display the input screen. Enter the following data
for a black oil produced from a field similar to that being modelled:
Formation GOR
Oil Gravity
Gas Gravity
Water Salinity
Mole % H2S
Mole % CO2
Mole % N2
820 scf/STB
34 API
0.833 s.g.
140000 ppm
0
0
0
Select Single Stage separation, Standing for Pb, Rs, Bo correlation and Beggs et al for
viscosity. To calculate data for plotting, click on Calc, select the Automatic option and
enter the following:
April 2001
Material Balance Program - Version 6
A-10
Appendices
Temperature
degrees F
Pressure
psig
210
210
1
100
6500
50
From
to
Steps
There is no match data, so continue on and compute PVT properties using the
standard correlations. Click on Calc twice to calculate the PVT properties. Click Plot
then select Pressure on the X-axis and Oil FVF on the Y-axis. Display the following
plot by clicking Done:
Click Done 3 times and return to the main menu.
Calculating the Oil in Place
At this stage of the field development, we have only exploration well data and
geophysical mapping data to define the oil-in-place. Therefore, a probabilistic reserves
estimate is required. This section outlines the steps required to carry out a Monte
Carlo reserves estimation.
Distributions Menu
Select Input - Distributions from the main menu to begin entering your estimates of
the reservoir properties. Accurate values for all parameters are not generally available,
however, a reasonable estimate of the likely range can made using available geological
and reservoir knowledge.
Select Area * Net Thickness for the reservoir volume calculation method, then enter the
following data on the Distributions input screen:
Statistics
Number of Cases
1000
Petroleum Experts
Appendix A - Examples A-11
Reservoir
Number of
Steps
Temperature
Pressure
Histogram 20
210 degrees F
5000 psig
Parameter
Distribution
Minimum
Maximum
Mode
Area
Thickness
Porosity
Oil Saturation
Solution GOR
Oil Gravity
Gas Gravity
Triangular
Triangular
Normal
Normal
Fixed Value
Fixed Value
Fixed Value
3000
100
7000
200
5000
150
Average
Std.
Deviation
0.2
0.7
0.05
0.1
500
34
0.7
Click Calc twice and the program will compute the stock tank oil originally in place
(STOIIP) as a function of expectation. Click Plot to display a relative frequency
histogram for STOIIP similar to that shown below:
Click Finish to return to the calculation screen, then click Result to display the STOIIP
for various probabilities. We are preparing a "most likely" production profile, so note
down the 50% probability STOIIP around 758 MMSTB. For future reference, generate
a report by clicking the Report button. As we do not have a gas cap, the OGIP will be
computed from the solution GOR, so there is no need to carry this value forward. Click
Done 3 times to return to the main menu.
Setting up the Forward Prediction
Select Material Balance from the Tool menu, then select Options from the main
menu. Make the following option selections:
Reservoir Fluid
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Oil
Material Balance Program - Version 6
A-12
Appendices
Tank Model
PVT Model
Production History
Compositional Tracking
Single Tank
Simple PVT
By Tank
No
Click Done to return to the main menu.
Re-enter the same PVT properties as for the Monte-Carlo analysis above.
Reservoir and Aquifer Input
Select Input - Tank Data. Select the Tank Parameters tab and enter the following
data:
Tank Type
Temperature
Initial Pressure
Porosity
Connate Water Saturation
Water Compressibility
Initial Gas Cap
Original Oil in Place
Start of Production
Oil
210
5000
0.20
0.25
Use Correlation
0
750 MMSTB
1/1/94
Note that the reservoir parameters used for the Material Balance calculation are not
necessarily identical to those input to the Monte Carlo simulation. For example, it is
expected that the material balance calculation would be repeated with STOIIP values
corresponding to the 10% and 90% probability levels as well as the "most likely" 50%
probability value.
Also, click the Monitor Contacts button ON, the Has Dry Gas Producers button OFF
and the Gas Coning button OFF.
Water Influx
Next, the aquifer properties must be entered. Click the Water Influx tab, then select
Hurst - van Everdingen - Dake from the drop down list. You will then be prompted to
enter the aquifer parameters:
System Type
Reservoir Thickness
Reservoir Radius
Outer/Inner Radius ratio
Encroachment Angle
Aquifer Permeability
Radial Aquifer
150 ft
8000 ft
5
360 degrees
50 millidarcies
Note that although it is often difficult to obtain definitive values for these parameters,
useful results can be obtained by a combination of geological input and calculating
sensitivities for a range of possible values. Click Done to return to the main menu.
Petroleum Experts
Appendix A - Examples A-13
Rock Properties
Next click on the Rock Properties tab and select the From Correlation button.
Pore Volume vs Depth
As we have requested MBAL to calculate the fluid contacts, the reservoir geometry
must be entered. Click the Pore Volume vs Depth tab and enter the following to set
up a simple tank model:
Pore Volume Fraction
Depth
0.0
1.0
9000 ft SS
10000 ft SS
Relative Permeability
Next click on the Relative Permeability tab. First select Corey Functions from the Rel
Perm from list box. Check that No is selected in the Modified list box. Enter the
following
Click Input - Residual Saturations and enter the following sweep efficiency and
residual saturation data:
Water Sweep
Efficiency
Gas Sweep Efficiency
100 percent
100 percent
Residual Saturations
Krw
Kro
Krg
Residual Saturation
End Point
Exponent
0.25
0.3
0.02
0.4
0.8
0.9
2
2
1.5
Click Plot to view the relative permeability curves.
Click Done and return to the main menu.
Production Prediction Setup
There is no history to match in this case, so go directly to prediction. Click Production
Prediction - Prediction Setup and enter the following selections:
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Material Balance Program - Version 6
A-14
Appendices
Predict:
With:
Prediction Start
Prediction End
Reservoir
pressure
and
production
From
manifold
pressures
schedules.
Water Injection and Voidage
Replacement with Water
Start of Production
Automatic
Click Done and return to the main menu. Click Production Prediction again, and you will
notice that many more selections are available.
Production Production and Constraints
This field is expected to be developed using a platform and pipeline system with a
maximum throughput of 120,000 STB/d. The separator operating pressure will be 250
psig. Select Production Prediction - Production and Constraints and enter the
following:
Time
Manifold
Pressure
Max Liquid
Rate
1/1/94
250
120000
Click Done and return to the main menu.
Well Type Definition
Select Production Prediction - Well Type Definition and create a new well by clicking
button next the the Well field. Enter the name, “OilWell” in the Well field.
on the
In the Setup tab, select the Well Type to be Oil Producer.
Click on the Validate button.
Inflow Performance
Click on the Inflow Performance tab. First select Straight Line + Vogel from the Inflow
Performance list box and enter a value of 16 STB/d/psi for P.I. Do not check PI
Correction for Mobility.
Next enter the breakthrough constraints. Set the position of the wells with respect to
the original oil/water contact by entering the following (You may have to change the unit
selection for this entry by clicking the (*) box to the left of the field):
Gas Saturation Breakthrough
Water contact Depth
Shift Relative Permeability to
Breakthrough
9800 ft
Yes
Petroleum Experts
Appendix A - Examples A-15
Outflow Performance
Click on the Outflow Performance tab. First enter the outflow performance. Select
Tubing Performance Curves from the Outflow Performance list box. Click the Edit
button to input the curves. In this example we are going to import a file containing the
lift curves from a file generated by the Petroleum Experts program, PROSPER. Click
Import and select the example lift curves file OILWELL.MBV. Note that you will have
to change the List Files of Type combo box to MBV files to be able to import the MBV
file.
Examine the lift curves by clicking Plot.
displayed:
A graph similar to the following will be
Click Finish and then Done to return to the Outflow Performance tab. Then set up the
well constraints by entering the following:
Maximum Drawdown
Maximum FWHP
Minimum FWHP
Maximum FBHP
Minimum FBHP
Minimum Liquid Rate
Maximum Liquid Rate
15000 STB/d
Set the abandonment constraints by entering the following (You may have to change
the unit selection for these entries by clicking the (*) box to the left of the field):
GOR Abandonment
WCT Abandonment
Allow Recovery after
abandonment
April 2001
5000 scf/STB
90 %
Yes
Material Balance Program - Version 6
A-16
Appendices
Click Done and return to the main menu.
Well Schedule
The next task is to enter the well schedule. We will assume that a total of 14 wells will
be drilled in the field, with 6 wells coming on line in each of the first two years, and a
further 2 wells are completed in the 3rd year. To set this schedule up, click on
Production Prediction - Well Schedule and enter the following:
Start Time
d/m/y
End Time
d/m/y
1/1/94
1/1/95
1/1/96
Number
Of Wells
Well Type
Definition
6
6
2
Oilwell
Oilwell
Oilwell
Down Time
Factor
As no end time has been entered, the program will shut the wells down automatically
according to the abandonment constraints that have been set. The well type definition
is selected from the drop down list that appears when the arrow is clicked. The names
on the list will correspond to those entered in the Well Type Definition section. Click
Done to return to the main menu.
Reporting Schedule
Leave the reporting schedule set to automatic (default) by clicking Production
Prediction - Reporting Schedule. Select Automatic, then click Done.
Running the Forward Prediction
Once all the input data has been entered, click Production Prediction - Run
Prediction then click Calc to begin the calculation sequence. The calculation will stop
when the wells gas oil or cannot flow. For this example, this should occur by the end of
1999. Plot the results by clicking Plot and selecting Average Oil Rate and Reservoir
Pressure as variables. A graph similar to the following will be displayed:
Petroleum Experts
Appendix A - Examples A-17
The oil production builds up to plateau level as more wells come on line. Dropping
reservoir pressure and water influx cause the production rate to decrease for a while.
A slight decrease in producing GOR is seen as the reservoir pressure goes below
bubble point and the evolved gas builds up to the critical saturation. Free gas is then
produced. This initially has a beneficial effect on oil production as the gas lightens the
fluid column. As the gas is depleted, field production enters a final decline as the
produced fluid density rises and the reservoir pressure depletes.
Save the results of this run as follows:
Return to the Production Prediction screen and click the Save button. Click on the
Add button and enter a descriptive name (e.g. no injection) for the new stream. Return
to the main menu.
Water Injection
The next step is to examine the effect of pressure maintenance by water injection. Go
back to Production Prediction - Prediction Setup. Make sure the Water Injection
and Voidage Replacement with Water options are selected. Then select Production
Prediction - Production and Constraints and append a new row with a date of 1st
January 1996 and 100% Voidage Replacement.
This will cause water to be injected into the tank to replace 100% of the produced liquid
from the tank.
Re-run the prediction. The reservoir pressure will be maintained at around 3480 psig
and the field life extended beyond the year 2000. To compare the results, click Plot Variables. Select Prediction and the previously saved calculation stream. A plot of
reservoir pressure and cumulative oil production for both cases is shown below:
April 2001
Material Balance Program - Version 6
A-18
Appendices
Save the file if desired as FORWARD.MBI.
Petroleum Experts
Appendix A - Examples A-19
A.3 Other Example Files
This section describes the other example MBI files that are installed with MBAL and a
brief explanation.
CALCWELL.MBI
Used by the CALCWELL.XLS open server example.
DETAILED2.MBI
Used by the DA2.XLS open server example.
FRACT FLOW MATCH1.MBI
Used by the FRACT_FLOW_MATCH1.XLS open server example.
FRACT FLOW MATCH2.MBI
Used by the FRACT_FLOW_MATCH2.XLS open server example.
GAS.MBI
Example of a single tank gas example.
MULTIGAS.MBI
Example of a multi-tank gas example.
MULTIOIL.MBI
Example of a multi-tank oil example.
MULTIPVT.MBI
Example of a variable PVT example.
OIL.MBI
Example of a single tank oil example.
SIMPLE2.MBI
Used by the DA1.XLS open server example.
STEP1.MBI
Used by the STEP1.XLS open server example.
STEP2.MBI
Used by the STEP2.XLS open server example.
STEP3.MBI
Used by the STEP3.XLS open server example.
April 2001
Material Balance Program - Version 6
References
1.
Argawal, R.G., Al-Hussainy, R., and Ramey, H.J., Jr.: "The Importance of
Water Influx in Gas Reservoirs," JPT (November 1965) 1336-1342.
2.
Bruns, J.R., Fetkovich, M.J., and Meitzer, V.C.: "The Effect of Water Influx on
P/Z Cumulative Gas Production Curves," JPT (March 1965), 287-291.
3.
Chierici, G.L., Pizzi, G., and Ciucci, G.M.: "Water Drive Gas Reservoirs:
Uncertainty in Reserves Evaluation From Past History," JPT (February 1967),
237-244.
4.
Cragoe, C.S.: "Thermodynamic Properties of Petroleum Product," Bureau of
Standards, U.S. Department of Commerce Misc, Pub., No. 7 (1929) 26.
5.
Dake, L.: "Fundamentals of Petroleum Engineering,"
6.
Dumore, J.M.: "Material Balance for a Bottom-Water Drive Gas Reservoir,"
SPEJ December 1973) 328-334.
7.
Dranchuk, P.M., Purvis, R.A. and Robinson, D.B.: "Computer Calculation of
Natural Gas Compressibility Factors Using the Standing and Katz Correlation,"
Institute of Petroleum, IP 74-008 (1974).
8.
van Everdingen, A.F. and Hurst, W.: "Application of the Laplace Transform to
Flow Problems in Reservoirs," Trans. AIME (1949) 186, 304-324B.
9.
Hall, K.R. and Yarborough, L.: "A New Equation of State for Z-factor
Calculations," OGJ (June 1973), 82-92.
10. Campbell, R.A. and Campbell, J.M.,Sr.: "Mineral Property Economics," Vol 3:
Petroleum Property Evaluation, Campbell Petroleum Series (1978).
11. Havlena, D. and Odeh, A.S.: "The Material Balance as an Equation of StraightLine," JPT (August 1963), 896-900.
12. Hurst, W.: "Water Influx into a Reservoir and Its Application to the Equation of
Volumetric Balance," Trans. AIME (1943) 151, 57.
13. Ikoku, C.U.: "Natural Gas Engineering," PennWell Publishing Co. (1980).
14. Kazemi, H.: "A Reservoir Simulator for Studying Productivity Variation and
Transient Behaviour of a Well in a Reservoir Undergoing Gas Evolution,"
Trans. AIME (1975) 259, 1401.
15. Lasater, J.A.: "Bubble Point Pressure Correlation," Trans. AIME (1958) 213,
379-381.
16. Lutes. J.L. et al.: "Accelerated Blowdown of a Strong Water-Drive Gas
Reservoir," JPT (December 1977), 1533-1538.
Appendix B - References
B-2
Appendices
17. Ramagost, B.P., and Farshad, F.F.: "P/Z Abnormally Pressured Gas
Reservoirs," paper SPE 10125, presented at the 1981 SPE Annual Technical
Conference and Exhibition, San Antonio Texas, October 1981.
18. Schlithuis, R.J.: "Active Oil and Reservoir Energy" Trans. AIME (1936) 118,
33-52.
19. Standing, M.B.: "Volumetric and Phase Behaviour of Oil field Hydrocarbon
Systems," SPE AIME, Dallas, 1977.
20. Steffensen, R.J. and Sheffield, M.: "Reservoir Simulation of a Collapsing Gas
Saturation Requiring Areal Variation in Bubble-Point Pressure," paper SPE
4275 presented at the 3rd Symposium on Numerical Simulation of Reservoir
Performance, Houston, Texas, 1973.
21. Tarner, J.: "How Different Size Caps and Pressure Maintenance Affect
Ultimate Recovery," Oil Weekly (June 12, 1994), 32.
22. Tehrani, D.H.: "An Analysis of Volumetric Balance Equation for Calculation of
Oil in Place and Water Influx," JPT (September 1985), 1664-1670.
23. Tehrani, D.H.: "Simultaneous Solution of Oil-in-Place and Water Influx
Parameters for Partial Water Drive Reservoir with Initial Gas Cap," paper SPE
2969, presented at the 1970 SPE Annual Fall Meeting, Houston Texas, Oct. 47.
24. Thomas. L.K., Lumpkin, W.B., and Reheis, G.M.: "Reservoir Simulation of
Variable Bubble-Point Problems," Trans. AIME (1976) 261, 10
25. Vogt, J.P. and Wang, B.: "A More Accurate Water Influx Formula with
Applications,", JCPT (Month. Year) pg-pg.
26. Vogt, J.P. and Wang, B.: "Accurate Formulas for Calculating the Water Influx
Superposition Integral", paper SPE 17066 presented at the 1987 SPE Eastern
Regional Meeting, Pittsburgh Pennsylvania, Oct. 21-23.
27. Wang, B. and Teasdale, T.S.: "GASWAT-PC: A Microcomputer Program for
Gas Material Balance with Water Influx", paper SPE 16484 presented at the
1987 Petroleum Industry Applications of Microcomputers Meeting,
Montgomery Texas, June 23-26.
28. Wang, B., Litvak, B.L. and Boffin II, G.W.: "OILWAT: Microcomputer Program
for Oil Material Balance with Gascap and Water Influx," paper SPE 24437
presented at the 1992 SPE Petroleum Computer Conference, Houston Texas,
July 19-22.
29. Wattenbarger, R.A., Ding, S., Yang, W. and Startzman, R.A.: "The Use of a
Semi-analytical Method for Matching Aquifer Influence Functions", paper SPE
19125 presented at the 1989 SPE PCC, San Antonio, Texas, June 26-28.
Petroleum Experts
Appendix B - References
B-3
30. Wichert, E. and Aziz, K.: "Calculation of Z's for Sour Gases," 51(5) 1972, 119122.
31. Standing, M.B. and Katz, D.L.: "Density of Natural Gases," Trans. AIME (1942)
146, 64-66.
32. Urbanczyk, C.H. and Wattenbarger, R.A.: "Optimization of Well Rates under
Gas Coning Conditions," SPE Advanced Technology Series, Vol. 2, No. 2.
April 2001
Material Balance Program - Version 6
MBAL Equations
C.1 Material Balance Equations
The following pages show some of the equations used in the MBAL program. Please
refer to a basic reservoir engineering text for a detailed treatment of graphical history
matching techniques.
C.1.1 OIL
F = NE + We
Where the underground withdrawal F equals the surface production of oil, water and
gas corrected to reservoir conditions:
(
)
(
) (
)
F = N p * Bo − B g * Rs + B g * G p − Gi + Wp − Wi * Bw and
the original oil in place is N stock tank barrels and E is the per unit expansion of oil
(and its dissolved gas), connate water, pore volume compaction and the gas cap.
E = ( Bo − Boi ) + ( Rsi − Rs ) * Bg + m * Boi
(
Bg
Bg 1
S *C +C 
− 1 + (1 + m) * Boi *  wc w f  * ( Pi − P)
 1 − Swc 
)
Graphical interpretation methods are based on manipulating the basic material balance
expression to obtain a straight line plot when the assumptions of the plotting method
are valid. For example, when there is no aquifer influx, We = 0, and:
F = NE
F
=N
E
A plot of F/E should be a horizontal straight line with a Y axis intercept equal to the oilin-place N. This plot is a good diagnostic for identification of the reservoir drive
mechanism. If the aquifer model is correct, the following manipulation shows that a plot
F − We = NE
of F-We against E will yield a straight line with a slope of N. The procedure is to adjust
the aquifer model until the best straight line fit is obtained. A more sensitive plot is
obtained by dividing through by E as follows:
W
F
=N− e
E
E
When the aquifer model is accurate, the plot of F/E vs We/E will yield a straight line with
unit slope and a y-axis intercept at N.
Appendix C- MBAL Equations
C-2
Appendices
C.1.2 GAS:
F = GE + We
Where:
(
)
(
F = B g * G pe − Gi + Bw * Wp − Wi
)
and
 S wc * C w + C f 
E = B g − Bgi + Bgi * 
 * ( Pi − P )
 1 − Swc 
(
)
C.1.3 OGIP Calculations:
∑(
n
σ (Y ) = 100 ( Y σ (−YY)
max
min
where: σ (Y ) =
)
Ycj − Y j
)
2
j =1
n −1
C.1.4 Natural Depletion Reservoirs:
F = G Eg
Can be converted to a more popular form
=
P
Z
Pi
Zi
[1 −
G w gp
G
].
C.1.5 Abnormally Pressured Reservoirs:
(
F = G E g + E fw
)
re-arrange the equation to obtain:
P
Z
1.
2.
3.
[1 − C ( P − P)] =
e
i
Pi
Z1
(1 − )
Gwgp
G
P/Z Method 2:
RF Modified P/Z Method:
HO Straight Line Method:
F
Eg
(
= G 1 + Bgi ce
Pi − P
Eg
)
➀
then the water influx (W e) is defined as We = U ( Pi − P ) and equation ➀ becomes:
F
Eg
(
= G + B gi G
ce
+U
)
Pi − P
Eg
Petroleum Experts
Appendix C
C-3
C.1.6 Water Drive Reservoirs:
F = G E g + We
P/Z Methods
P
Z
=
Pi
Zi
G-G wgp
G-Y
where:
Y=
G wgp Bg
Eg
=G+
Pi
Zi Psc
Tsc
T
(W
e
− Wp B w
)
Cole Method:
We − Wp Bw
Eg
HO Straight Line Method:
F
Eg
April 2001
= G + U S(EP,t )
g
Material Balance Program - Version 6
C-4
Appendices
C.2 Aquifer Models
In the following sections, the various aquifer models available in MBAL are desribed
along with the references.
C.2.1 Small Pot
This model assumes that the aquifer is of a fixed volume Va and the water inlux from
the aquifer to the reservoir is time independent. The influx from the aquifer is related to
the pressure drop through the total average compressibility of the system (water +
rock). The equation describing the influx is thus given by,
We (t ) = 5.615(C w + C f )Va ( Pi − Pn )
(Eq1.1a)
where
Va = aquifer volume
Pi = Initial pressure
Pn = Pressure at time t.
Cw = Water compressibilty
Cf = Rock compressibility
See Dake L.P.: “ Fundamentals of reservoir engineering”, Chapter 9 for more details.
C.2.2 Schilthuis Steady State
This model assumes that the flow is time dependent but is a steady state process. It
approximates the water influx function by,
dWe
= Ac (Pi − P )
dt
(Eq1.2a)
where, Ac is the productivity constant of the aquifer in RB/psi/day. Assuming it is
constant over time, this equation on integration gives,
We (t ) = Ac ∫ (Pi − P )dt
t
(Eq1.2b)
0
The numerical approximation for this integral is done using the following formula with
W e expressed is MMRB,
n
(Pj + Pj −1 )(

W e (t ) = 10 −6 Ac ∑  Pi −
 t j − t j −1 )
2
j =1 

(Eq1.2c)
Petroleum Experts
Appendix C
C-5
The pressure decline is approximated as shown in the following diagram
Reservoir Pressure decline approximation with time
See Tehrani D.H. : “ Simultaneous Solution of Oil-In-Place and Water Influx
parameters for Partial Water Drive reservoirs with Initial Gas Cap”, SPE 2969 for more
details.
C.2.3 Hurst Steady State
It is another simplified model. The influx is defined by the following equation
dWe Ac (Pi − P )
=
dt
log(α × t )
(Eq1.3a)
The influx is found by integrating,
We = ∫
t
0
Ac (Pi − P )
dt
log(α × t )
(Eq1.3b)
The numerical approximation to this integral is with the influx in MMRB,
n
(Pj + Pj −1 ) (t j − t j −1 )

W e (t ) = 10 −6 Ac ∑  Pi −

2
j =1 
 ln (α × (t j − t 0 ))
(Eq1.3c)
Where Ac is the aquifer constant entered in the aquifer model input and has units
RB/psi/day.
See Tehrani D.H. : “ Simultaneous Solution of Oil-In-Place and Water Influx
parameters for Partial Water Drive reservoirs with Initial Gas Cap”, SPE 2969 for more
details.
April 2001
Material Balance Program - Version 6
C-6
Appendices
C.2.4 Hurst-van Everdingen-Dake
All the models previously discussed with the exception of Hurst simplified are based on
the assumption that the pressure disturbance travels instantaneously throughout the
aquifer and reservoir system. On the other hand if we do not make this assumption but
rather say that the speed will depend on the pressure diffusivity of the system.
Radial System
The pressure diffusivity equation representing the behavior for a radial system can be
written as,
1 ∂  ∂PD  ∂PD
=
 rD
rD ∂rD  ∂t D  ∂t D
(Eq1.4a)
where
rD =
r
ro
tD =
 φµ (C w + C f )ro2 

= t /


α
k


ro being the outer radius of the reservoir
t
(Eq1.4b)
α is pressure diffusivity of the system and is also called tD constant in MBAL.
φ
=
Porosity
µ
=
Viscosity of water
Cw
=
water compressibility
Cf
=
Formation compressibility
k
=
Permeability of the aquifer.
In modeling aquifer behavior since we are interested in finding rates with pressure
changes, this diffusivity equation solved for constant terminal pressure i.e. constant
pressure at reservoir-aquifer boundary gives the following general solution,
We = U × ∆P × WD (t D , RD )
(Eq1.4c)
where
RD
= reservoir radius/ aquifer outer radius
U is called aquifer constant and in field units it is given by,
U=
Ae
h
1.119 Aeφh(C f + C w )ro2
360.0
=
=
Encroachment angle in degrees
Reservoir thickness in feet
Petroleum Experts
Appendix C
C-7
Similarly the tD constant in oil field units (day-1) is given by,
α=
2.309k a
365.25φµ w (C f + C w )ro2
The function WD is called dimensionless aquifer function and is depends on
dimensionless time and the size of the aquifer with respect to the reservoir. There are
algebraic approximations to the WD function available.3 This form is the most general
form of the equation as it gives the behavior of the pressure diffusivity equation for both
the finite and infinite acting aquifers (bounded) depending on the value of RD.
In real production, this terminal pressure (at the reservoir-aquifer boundary) does not
remain constant, but changes. Hurst-Van-Everdingen and Dake using the principle of
superposition solved this problem. They found the real-time water influx using Eq1.4c
and approximating the pressure decline as a step function shown as dashed lines in
figure1. The water influx equation thus after superposition is given by,
We (t ) = 10 −6 ∑ U∆PjWD (α (t n − t j ), RD )
n −1
(Eq1.4d)
j =o
And,
∆Pj = (Pj −1 − Pj +1 ) 2 If j=0 i.e. the first, use Pi i.e. initial reservoir pressure,
instead of Pj-1
Linear Aquifers
The pressure diffusivity equation as represented for the radial can also be set up for
linear aquifers and a constant terminal pressure solution found. The form of the
solution is exactly similar to the radial one, except for the definition of tD constant and
U. These are defined as,
We (t ) = 10 −6 ∑ U∆PjWD (α (t n − t j ))
n −1
(Eq1.4e)
j =o
α=
2.309k
365.25φµ w (C f + C w )L2a
U = 106Va (C f + Cw ) 5.615
Where,
106Va
La =
(Wrφh )
Va = Aquifer volume
W r = Reservoir width
La= length of the aquifer
April 2001
Material Balance Program - Version 6
C-8
Appendices
Bottom Drive
The bottom drive aquifer models are the same as the linear models. The only
difference from linear models is the surface through which the influx is taking place. For
bottom drive aquifers the surface available from influx is rw2. The length used for
finding the tD constant is the dimension perpendicular to this surface. These are
calculated in oil field units as follows
α=
2.309ka
365.25φµ w (C f + Cw )L2a
U = 106Va (C f + Cw ) 5.615
Where
La
10 6 V a
=
π r o2 φ
(
)
In equation Eq1.4e the form of the influx function depends on the boundary conditions
considered at the outer aquifer boundary. The boundary conditions available within
MBAL are
Infinite acting
This form assumes that the aquifer length is infinite, the value of aquifer length is
infinite. However for finding tD constant the value of La can be an arbitrary
constant. In MBAL we choose a very large value for Va and then estimate La.
Sealed boundary
This form takes the aquifer to be finite with a length La and finds the aquifer
function as of this value.
Constant pressure boundary
This form assumes that during the whole time the outer boundary of the aquifer
is at a constant pressure.
Note In all the original models the constant U is treated as constant all through the
time. However in MBAL, while doing summations during superposition, U value
components like compressibility and PVT properties are evaluated at the current
reservoir pressure.
See Dake L.P.: “ Fundamentals of reservoir engineering”, Chapter 9 and Nabor et al. : “
Linear Aquifer behaviour”, JPT May 1964, SPE 791 for more details.
C.2.5 Hurst-van Everdingen-Odeh
The Hurst-van Everdingen-Odeh model is essentially the same as the Hurst-van
Everdingen-Odeh model. The only difference is instead of entering all the aquifer
dimensions to evaluate aquifer constant and tD constant we enter the values of the
constants as directly.
The dimensionless solutions i.e. W D functions are still the same as of the Hurst-van
Everdingen Dake method.
Petroleum Experts
Appendix C
C-9
C.2.6 Vogt-Wang
This model is exactly the same as the Hurst-van Everdingen-Dake modified model. It
also assumes a linear pressure decline in each time step. To find the influx in each
time step, it uses the convolution theorem to give the following expression for influx,
∆P D
We = U ×
WD (t D − τ )dτ
t D ∫0
t
(Eq1.7a)
Since, the function still is linear, it uses superposition and the water influx is
approximated as,
t
 Pi − P1 t D1

P1 − P2 D 2
−
+
−
+
(
)
(
)
......
τ
τ
τ
τ
W
t
d
W
t
d


D Dn
∫ D Dn
t D 2 − t D1 t∫D1
 t D1 0

We (t Dn ) = U 

t Dn
+ Pn−1 − Pn W (t − τ )dτ

 t Dn − t Dn−1 t ∫ D Dn

Dn −1


(Eq1.7b)
For each time step the convolution integral for each time step can be broken into two
integrals by change of variable from as follows,
∫ W (t
t Di +1
D
Dn
− τ )dτ =
∫ W (u )du − ∫ W (u )du
t Dn −t Di
t Dn − t Di +1
D
D
0
t Di
(Eq1.7c)
0
This substitution into the water influx function gives the following result with influx as
MMRB
We (t n ) = 10 U ∑ ∆Pj ∫ WD (t D ) × t D
−6
n −1
t Dj
j =o
o
Where
if j = 0,
Otherwise,
∆Pj =
(Eq1.7d)
∆P0 =
P1 − P0
α (t1 − t0 )
Pj +1 − Pj
P − Pj −1
− j
α (t j +1 − t j ) α (t j − t j −1 )
See Vogt J.P. and Wang B.: “ Accurate Formulas for Calculating the Water Influx
Superposition Integral.”, SPE 17066 for more details.
C.2.7 Fetkovitch Semi Steady State
In the semi-steady state model, the pressure within the aquifer is not kept constant but
allowed to change. Material balance equation is used to find that the changed average
pressure in the aquifer. Based on this fact the influx is worked out to be,
We =
April 2001

 JP
Wei
(Pi − P )1 − exp − i
Pi
 Wei




(Eq1.9a)
Material Balance Program - Version 6
C-10
Appendices
Where Wei is the maximum encroachable water influx, J is the aquifer productivity
index. Pi is the initial pressure and P is the reservoir pressure. For different flow
geometry the values of these two constants are:Radial Model
(
)
Wei = 3.14159(C f + C w )Ae rw2 Rd2 − 1 hφPi 360.0 * 5.615
J=
0.00708 Ae k a h
360.0µ w log 2 ( Rd )
Linear Model
Wei = 10 6 (C w + C f )Va P0 5.615
J=
0.00127k a hWr
µ w La
La =
10 6 Va
Wr hφ
Bottom Drive
Wei = 10 6 (C w + C f )Va P0 5.615
J=
0.00127 k aπrw2
µ w La
La =
10 6 Va
πrw2φ
This influx equation Eq1.9a is still valid only for a constant reservoir pressure P. In case
the reservoir pressure also is declining; the influx is calculated using the principle of
superposition. For the first time step, the influx is,
W1 =
Wei
Pi − P1
Pi
(
)1 − exp − WJP ∆t  


i
1
ei

(Eq1.9b)
th
For the n time step the influx is,
Wn =
Wei
Pan − Pn
Pi
(
)1 − exp − WJP ∆t


i
ei
n

 


(Eq1.9c)
Where Pan and Pn are the average aquifer and reservoir pressure in the time
step.
Petroleum Experts
Appendix C
C-11
These are calculated as follows,
P − Pn
and
P0=PI
Pn = n−1
2
n −1

 ∑W j
j =1

Pan = Pi 1 −
Wei








Based on these the superposition formula gives the following result for aquifer influx in
MMRB,
We = 10 − 6 ∑
n −1
Wei
j = 0 Pi
P + Pj +1 

 1.0 − e − X
 Paj − j
2


(
)
(Eq1.9d)
Where
X = JPi (t j +1 − t j ) Wei
 W
PL = Pi 1 − last
Wei


 ,

W last being the aquifer influx up to j-1 time step.
See Fetkovich M.J.: “ A Simplified Approach to Water Influx calculations --- Finite
Aquifer System”, SPE 2603 for more details.
C.2.8 Fetkovitch Steady State
The Fetkovich theory looks at water influx as well inflow calculated using productivity
index. Thus, the influx rate is a function given as,
dWe
= J (Pi − P )
dt
(Eq1.8a)
In the steady state model, the productivity index is calculated similar to a Darcy well
inflow model. This PI is supposed to remain constant. Depending on the geometry the
PI is calculated as follows in oil field units:Radial
J=
0.00708 Ae k a h
360.0µ w (log(Rd ) − 0.75)
Linear
0.00381k a hWr
J=
µ w La
Bottom Drive
0.00381k aπrw2
J=
µ w La
See Fetkovich M.J.: “ A Simplified Approach to Water Influx calculations --- Finite
Aquifer System”, SPE 2603 for more details.
April 2001
Material Balance Program - Version 6
C-12
Appendices
C.2.9 Hurst-van Everdingen Modified
This method is similar to the Hurst-van Everdingen Dake model. The main difference is
the manner in which the pressure decline is approximated. In the original model the
decline is approximated as a series of time steps with constant pressure. In the
modified one it is approximated as a linear decline for each time step. As shown in the
solid lines of figure1. This approach allows us to have varying rate within a time step
rather than it being constant as in the original method. The solution for this case is the
integral of the dimensionless solution of the constant terminal pressure case.
We = U ∫ WD (t D )dP
P
(Eq1.6a)
Pi
This solution changed into time domain becomes,
tD
dP
We = ∫ WD (t D )
dt D
dt
D
0
Since pressure decline with time is linear, dP
(Eq1.6b)
dt D
is a constant equal to slope of
the linear pressure decline, given by,
dP 1 Pi − P
=
dt D α t
The influx function thus becomes for the linear decline,
(P − P ) t D ( )
We = U × i
WD t D dt D
α × t ∫0
(Eq1.6c)
Since the functions are still linear, we can use superposition again. Thus, if we
approximate the pressure decline by a series of linear declines, the water influx solution
is given by,
t
n −1
U ∆Pj Dn
−6
We (t n ) = 10 ∑
(Eq1.6d)
∫ WD (t D )dt D
j = o α t j − t j +1 t Dj
Where the form of WD, tD constant and U depend on the model being linear, bottom
drive or radial and are same as the ones used in original Hurst-van Everdingen model.
Petroleum Experts
Appendix C
C-13
C.2.10 Carter-Tracy
The principal difference between this method and the Hurst-van Everdingen models is
as follows. The Hurst-van Everdingen models assume a constant pressure over a time
interval and thus use the constant terminal pressure solution of the diffusivity equation
with the principle of superposition to find the water influx function. Carter Tracy model
on the other hand uses the constant terminal rate solution and expresses the aquifer
influx as a series of constant terminal rate solutions. The dimensionless function thus is
the pressure written ad PD function. The water influx equation thus by Carter Tracy
method is,
We (t n ) = 10 U ∑
n −1
−6
∆Pj − We (t n −1 )PD' (t Di )
j =o
PD (t Di ) − t Di PD' (t Di )
(t Di +1 − t Di )
(Eq1.10)
Where the various constants are defined as,
∆Pj = (P0 − Pj +1 )
t Di = α (t i − t 0 )
α=
U=
2.309ka
365.25φµ w (C f + Cw )rw2
1.119 Aeφh(C f + C w )rw2
360.0
The form of the equation is such that we do not need superposition to calculate the
water influx, but only the water influx up to previous time step. As such because of the
constant rate solution being the generator, it is basically a steady-state model. Also, it
is used only for radial geometry.
For each term in the summation MBAL uses the fluid properties at the pressure for the
time in the summation term. So in the summation formula above, alpha is calculated
using the fluid properties with the pressure at time tj. This is an improvement to the
original model where the fluid properties were taken from the pressure at tn.
See Carter R.D. and Tracey G.W. : “ An Improved Method for Calculating Water Influx”,
JPT Sep. 1960, SPE 2072 for more details.
April 2001
Material Balance Program - Version 6
C-14
Appendices
C.3 Relative Permeability
The equations shown below cover the Corey functions and Stones modifications to the
relative permeability functions.
C.3.1 Corey Relative Permeability Function :
In a Corey function, the Relative Permeability for the phase x is expressed as :
 Sx − Srx nx

Krx = Ex * 
 Smx − Srx 
where :Ex is the end point for the phase x,
nx the Corey Exponent,
Sx the phase saturation,
Srx the phase residual saturation and
Smx the phase maximum saturation.
The phase absolute permeability can then be expressed as :
Kx = K * Krx
where :
- K is the reservoir absolute permeability and
- Krx the relative permeability of phase x.
C.3.2 Stone method 1 modification to the Relative
Permeability Function :
Kro = Krocw * SSo * Fw * Fg
where :Krocw = oil relative permeability in the presence of connate water only,
SSo =
So − Sor
1 − Swco − Sor
Fw =
Krow
Krocw * (1 − SSw)
Fg =
Krog
Krocw * (1 − SSg)
when So > Sor
Krog = gas relative permeability in the presence of oil, gas and connate water,
Petroleum Experts
Appendix C
C-15
Krow = oil relative permeability in the presence of oil and water only.
and where :SSw =
Sw - Swco
1 − Swco - Sor)
SSg =
Sg
1 − Swco - Sor)
when Sw > Swco
C.3.3 Stone method 2 modification to the Relative
Permeability Function :

  Krow
  Krog

Kro = Krocw *  
+ Krw * 
+ Krg − Krw − Krg
  Krocw


  Krocw
Krog = gas relative permeability in the presence of oil, gas and connate water,
Krow = oil relative permeability in the presence of oil and water only.
Krocw = oil relative permeability in the presence of connate water only,
April 2001
Material Balance Program - Version 6
C-16
Appendices
C.4 Nomenclature:
Awe
Bg
Bo
Bt
Bw
Cf
Cw
Efw
Eg
Eo
Er
Et
Ev
F
Ft
G
Gi
GLp
Gp
Gt
Gwgp
h
HCPV
Kc
Ktd
Ktd
k
Krg
Kro
Kw
Kwrg
L1
L2
MLc
m
N
Np
OGWC
P
P1
Fraction of reserovir area invaded by water influx
gas formation volume factor
single-phase oil formation factor
two-phase oil formation factor
water formation volume factor
formation compressibility
water compressibility
expansion of water and reduction in pore volume
expansion of gas
expansion of oil and solution gas
recovery efficiency
overall expansion of oil, gas and water & formation
volumetric sweep efficiency
underground withdrawal
total trapped gas volume in HCPV
original gas in place
cumulative gas injection
cumulative condensate produced
cumulative dry gas production
trapped wet gas
cumulative wet gas produced
net thickness
hydrocarbon pore volume
condensate conservation factor
dimensionless time coefficient
theoretical dimensionless time coefficient
absolute permeability
gas relative permeability
oil relative permeability to gas
effective permeability to water in the aquifer
effective permeability to water at residual gas saturation
distance of linear gas reservoir at current gas water contact
distance of linear gas reservoir at original gas water contact
molecular weight of condensate
initial gascap size, defined as the ratio of initial gascap HCPV to initital oil zone
HCPV oil in place
original
cumulative oil production
original gas water contact
average reservoir pressure
average pressure in front of current gas water contact
Petroleum Experts
Appendix C
P2
Pb
Pt
Pwf
qo
qw
Qd
r1
r2
ra
re
rg
ro
rw
Rp
Rs
S
Sgc
Sgr
Sor
Swi
S(P,t)
T
t
tD
TDF
U
U
Vaq
W
We
Wi
Z
φ
Θ
µ
Ψ
γc
γw
σ
April 2001
C-17
pressure at original gas water contact
bubble-point pressure
average pressure in water invaded region
flowing bottomhole pressure
oil production rate
water influx rate
dimensionless water influx
radius of gas reservori at current gas water contact
rg
aquifer radius
external radius
radius of gas reservoir at original gas water contact
radius of oil reservoir at original oil water contact
wellbore radius
cumulative gas-oil ratio
instantaneous producing gas-oil ratio
well skin factor
critical gas saturation
residual gas saturation
residual oil saturation to water
initial water saturation
aquifer function
reservoir temperature
time
dimensionless time
dimensionless time adjusting factor
aquifer constant
theoretical aquifer constant
pore volume of aquifer
width of linear reservoir
cumulative water influx
cumulative water injection
gas deviation factor
porosity
dip angle
viscosity
influx encroachment angle
specific gravity of condensate
specific gravity of formation water
normalized standard deviation
Material Balance Program - Version 6
C-18
Appendices
C.4.1 Subscripts
a
aw
g
i
j
o
1
2
sc
t
w
minimum abandonment pressure condition
watered-out abandonment condition
gas
initial condition
index of loops
oil
location at current gas water contact
location at original gas water contact
standard condition
trapped gas in water invaded region
water
Petroleum Experts
Trouble Shooting Guide
This appendix describes some of the common problems experienced and questions
asked by users of MBal.
D.1 Prediction not Meeting Constraints
Question:
The production prediction calculation is not meeting the constraints that I entered in the
Production Prediction-Production and Constraints dialog.
Answer:
The only method that Mbal has to control the production (and thus meet constraints) is
to modify the manifold pressure. If Mbal is failing to meet the constraints it is most likely
that modifying the manifold pressure can not control the production. A symptom of this
problem is that the calculated manifold pressures are reported as 40,000 - this is the
upper limit that MBal uses for the manifold pressure before giving up. There are various
remedies for this problem.
•
•
•
In the well definition-outflow tab dialog, check that you are not using the
constant FBHP. If you are, Mbal has no way to control the production so can
not meet constraints. In this case you must use Tubing Performance Curves
to model the well.
Also in the well definition-outflow tab dialog, check that you have switched
Extrapolate TPC's on for all the wells. If not, then Mbal can not control the
production if the manifold pressure goes outside of the range of your Tubing
Performance Curves. You may also wish to regenerate your Tubing
Performance Curves with a wider range of manifold pressures to ensure
accurate results.
Also in the well definition-outflow tab dialog, check that the Tubing
Performance Curves have more than one manifold pressure.
D.2 Production Prediction Fails
Question:
In the Production Prediction-Run Prediction, I clicked on the Calc button but
immediately got a message box saying that the "The calculation is complete" and no
results were displayed.
Answer:
There are a number of reasons why this may happen but the immediate reason is
usually that the prediction is stopping prematurely because the rate has dropped to
zero. However it is difficult to diagnose the problem unless MBal can produce results of
some sort.
So the first step is to force the calculation to keep going. Go back to Production
Prediction-Prediction Setup and change the Prediction End to User Defined and
enter a date some time after the start of the prediction. Now rerun the prediction and it
Appendix D - Trouble Shooting Guide
D-2
Appendices
should produce results of some sort. It should now be possible to diagnose why the
calculation fails - firstly by examining the well results.
D.3 Pressures in the Prediction are Increasing (With No
Injection)
Question:
In history simulation or production prediction the pressure is increasing but I do not
have any injection.
Answer:
Although there are a number of obscure reasons for this problem the most common
reason is errors in the PVT input. Use the PVT-Calculator option to calculate
properties and verify each one in turn. In particular, check the Bo and/or Bg as these
are crucial to the material balance calculation.
D.4 Reversal in the Analytic Plot
Question:
In history matching-analytic plot the simulated data is going backwards or even looping
- why is this happening?
Answer:
For the single tank, the analytic plot calculates the primary phase rate from the input
tank pressure and non-principal phase rates (as well as the reset of the tank
description). For example, for an oil tank, it will calculate the cumulative oil rate from
the input tank pressure, water production, gas production, water injection and gas
injection. The calculation is done this way because it is much faster than calculating the
pressure from all the rates - and speed is critical when doing a regression.
This means that if there is an error in the estimates of the input data, MBal may only be
able to maintain the input tank pressure by reinjecting oil. For example, imagine that
the aquifer size has been underestimated. MBal will have to reinject oil to compensate
for the lack of aquifer.
To summarise, if reversal is observed in the simulated data, either the estimates of the
tank parameters are in error or there are errors in the production data.
D.5 Difference between History Simulation and Analytic Plot
Question:
I have done a match in the analytic plot and get a good visual match in the final
pressure. I then did a history simulation but get a poor match on the final pressure.
Answer:
For the single tank, the analytic plot calculates the primary phase rate from the input
tank pressure and non-principal phase rates (as well as the reset of the tank
description). For example, for an oil tank, it will calculate the cumulative oil rate from
the input tank pressure, water production, gas production, water injection and gas
Petroleum Experts
Appendix D - Trouble Shooting Guide
D-3
injection. The calculation is done this way because it is much faster than calculating the
pressure from all the rates - and speed is critical when doing a regression.
Traditionally one tends to look for the difference in the vertical separation between the
input and simulated data when assessing the quality of a match. However because we
are calculating the cumulative oil you actually need to look at the horizontal separation
between the input and simulated data. A match can appear to be of good quality if you
look at the vertical separation but actually be relatively poor if examined in the
horizontal direction.
The history simulation does the reverse calculation - it calculates the tank pressure
from the various input rates. Therefore you should be examining the vertical difference
between the tank history pressure and the simulated pressure when assessing the
quality of the match.
D.6 Dialogs Are Not Displayed Correctly
Question:
Some of the dialogs in Mbal are not displayed correctly. In particular, they are too big
for the screen so the buttons are not visible.
Answer:
This problem is due to screen resolution. The simplest fix is to change the Screen
Resolution in Mbal. Select the File – Preferences menu item in Mbal and try each of
the options in the Screen Resolution combo box in turn until you find one that displays
the dialogs correctly.
April 2001
Material Balance Program - Version 6