PVTi
Reference Manual
2008.1
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Table of Contents
List of Figures ..... ...................................................................................................................................................................7
List of Tables ...... ...................................................................................................................................................................8
Chapter 1 - New developments........................................................................................................ 9
Developments for 2007.1 .......................................................................................................................................................9
Developments for 2005A ......................................................................................................................................................10
Developments for 2004A ......................................................................................................................................................11
Chapter 2 - The Most Asked Questions About PVTi.................................................................... 15
Introduction......... .................................................................................................................................................................15
Chapter 3 - Introduction ................................................................................................................. 27
General information ..............................................................................................................................................................27
Chapter 4 - Getting started............................................................................................................. 31
Starting PVTi ...... .................................................................................................................................................................31
Chapter 5 - Tutorials ....................................................................................................................... 32
Overview............. .................................................................................................................................................................32
Fluid Properties Estimation...................................................................................................................................................34
Creating a fluid system .........................................................................................................................................................37
Simulating experiments ........................................................................................................................................................43
Fitting an equation of state to experimental results ..............................................................................................................50
Exporting ECLIPSE Black Oil PVT tables.............................................................................................................................54
Converting a black oil run to compositional..........................................................................................................................58
Workflow Tutorial .................................................................................................................................................................61
Multiphase Flash .................................................................................................................................................................69
Exporting an ECLIPSE Thermal model ................................................................................................................................73
Data analysis and quality control..........................................................................................................................................77
Removing contamination from samples................................................................................................................................84
Converting old projects to the current version ......................................................................................................................87
Chapter 6 - Reference section ....................................................................................................... 89
General information ..............................................................................................................................................................89
Main PVTi window ................................................................................................................................................................90
The PVTi main module .........................................................................................................................................................91
The fluid model ... .................................................................................................................................................................98
COMB - Compositional Material Balance ...........................................................................................................................112
Simulation using PVTi ........................................................................................................................................................117
Regression in PVTi.............................................................................................................................................................126
Exporting keywords ............................................................................................................................................................133
VFP module........ ...............................................................................................................................................................138
Utilities ................ ...............................................................................................................................................................144
Batch system and keywords...............................................................................................................................................152
Error handling ..... ...............................................................................................................................................................165
Chapter 7 - Keywords ................................................................................................................... 167
PVTi keywords.... ...............................................................................................................................................................167
Keywords A-D..... ...............................................................................................................................................................168
ACF: Acentric factors......................................................................................................................................................... 169
ACHEUH: A-coefficient for Cheuh-Prausnitz BICs............................................................................................................ 170
PVTi Reference Manual
Table of Contents
3
ALLDRY: Dry Gas Tables for Each Sample ...................................................................................................................... 171
BIC: Binary interaction coefficients .................................................................................................................................... 172
BLACKOIL: Start of the BLACKOIL section....................................................................................................................... 174
CALVAL: Specify calorific values....................................................................................................................................... 175
CHARACT: Components to be characterized.................................................................................................................... 176
CNAMES: Component names ........................................................................................................................................... 177
COATS: Blackoil tables...................................................................................................................................................... 178
COMB: Start of the COMB section .................................................................................................................................... 179
COMBINE: Group existing components ............................................................................................................................ 180
CORRACF: Splitting correlation for ACFs ......................................................................................................................... 181
CORRCP: Splitting correlation for critical properties ......................................................................................................... 182
DRYGAS: Dry gas tables................................................................................................................................................... 183
DEADOIL: Dead oil tables ................................................................................................................................................. 184
DEBUE: Select output to debug file................................................................................................................................... 185
DEBUG: Select output to debug file................................................................................................................................... 186
DEFBIC: Default binary interaction coefficients ................................................................................................................. 187
DEGREES: Temperature convention ................................................................................................................................ 188
DIFFERENTIAL: Blackoil tables ........................................................................................................................................ 189
DREF: Reference densities ............................................................................................................................................... 190
Keywords E-K ..... ...............................................................................................................................................................191
ECHO: Insert PVI file into PVP file ...................................................................................................................................... 192
EOS: Defines the required Equation of State ..................................................................................................................... 193
EOSOUT: EoS data for ECLIPSE 300................................................................................................................................. 194
EXP: Experiments .............................................................................................................................................................. 195
EXPIND: Set Status of Experiments .................................................................................................................................. 200
FIT: Perform fit by regression ........................................................................................................................................... 201
FRAC: Specify plus fraction data ........................................................................................................................................ 202
FRAGOR: Blackoil tables ..................................................................................................................................................... 203
FVFREF: FVF reference conditions.................................................................................................................................... 204
GI: Define GI nodes for E200 tables ................................................................................................................................. 205
GROUP: Start of the GROUP section.................................................................................................................................. 206
GRBYALL: Start of the GROUP section.............................................................................................................................. 207
GRBYMIX: Start of the GROUP section.............................................................................................................................. 208
GRBYSAM: Start of the GROUP section.............................................................................................................................. 209
GRPBYWGT: Grouping by molecular weight ........................................................................................................................ 210
HYDRO: Define component as hydrocarbon or non-hydrocarbon....................................................................................... 211
KVTABLE: Request K-value table for ECLIPSE 300 output ............................................................................................... 212
Keywords L- O .... ...............................................................................................................................................................213
LBC: Lohrenz-Bray-Clark viscosities.................................................................................................................................. 214
LBCCOEF: Set non-default LBC coefficients ...................................................................................................................... 215
LIVEOIL: Live oil tables .................................................................................................................................................... 216
LNAMES: Specify library names.......................................................................................................................................... 217
MAXIT: Max. number of regression iterations.................................................................................................................... 218
MAXSTEP: Maximum step size allowed in regression ........................................................................................................ 219
MDP: Data for Whitson splitting .......................................................................................................................................... 220
MESSAGE: Echo message to file and screen...................................................................................................................... 221
MINDELP: Minimum pressure difference ........................................................................................................................... 222
MINSTEP: Minimum step limit allowed in regression ......................................................................................................... 223
MIX: Mix samples .............................................................................................................................................................. 224
MODSPEC : Denotes start of the run specification section .................................................................................................. 225
MODSYS : Start of the MODSYS section ........................................................................................................................... 226
MOSES : Blackoil tables ..................................................................................................................................................... 227
MW : Specify molecular weights......................................................................................................................................... 228
MWS : Define plus fraction mole weight for CMF splitting .................................................................................................. 229
NCOMPS : Specify number of components ..................................................................................................................... 230
NEWPVI : Request new output PVI file ............................................................................................................................ 231
NEWPVO : Request new output PVO file......................................................................................................................... 232
NOECHO : No insertion of PVI file into PVP file ................................................................................................................ 233
OBS : Specify observations.............................................................................................................................................. 234
4
PVTi Reference Manual
Table of Contents
OBSIND : Specify observation weights ............................................................................................................................ 235
OMEGAA/B: Specify EoS omega values........................................................................................................................... 237
OPTIONS : Set various program options ......................................................................................................................... 238
OUTECL3 : Start of the OUTECL3 section ...................................................................................................................... 240
Keywords P- S .... ...............................................................................................................................................................241
PARACHOR : Define parachors ........................................................................................................................................... 242
PCRIT : Critical pressures................................................................................................................................................ 243
PEARCE : Blackoil tables................................................................................................................................................. 244
PEDERSEN : Specify Pedersen viscosities..................................................................................................................... 245
PRCORR : Peng-Robinson correction ............................................................................................................................. 246
PSEUCOMP : Start of the PSEUCOMP section.................................................................................................................. 247
RECOVERY : Liquid production for recovery estimates................................................................................................... 248
REGRESS: Start of the REGRESS section....................................................................................................................... 249
REGTARG : Regression target ........................................................................................................................................ 250
RTEMP : Reservoir temperature for ECLIPSE Compositional......................................................................................... 251
RUNSPEC : Denotes start of the run specification........................................................................................................... 252
SALINITY : Specify sample salinity ................................................................................................................................. 253
SAMPLE : Specify fluid sample ........................................................................................................................................ 254
SAMPLES : Specify fluid samples.................................................................................................................................... 255
SAMPLES : Specify fluid samples.................................................................................................................................... 256
SAMTITLE : Specify titles of fluid samples....................................................................................................................... 257
SAVCOMP : Save compositions ...................................................................................................................................... 258
SCT : Defines Semi-Continuous Thermodynamics split................................................................................................... 259
SG : Specify specific gravity............................................................................................................................................. 260
SIMULATE : Start of the SIMULATE section.................................................................................................................... 261
SPECHA-D: Specify specific heat capacity coefficients.................................................................................................... 262
SPLIT : Start of the SPLIT section................................................................................................................................... 263
SSHIFT : Dimensionless volume shifts for PR3 ................................................................................................................ 264
STCOND : Standard conditions......................................................................................................................................... 265
SYSTEM : Start of the SYSTEM section ........................................................................................................................... 266
Keywords T - Z ... ...............................................................................................................................................................267
TBOIL : Specify boiling points.......................................................................................................................................... 268
TCRIT : Specify critical temperatures............................................................................................................................... 269
THERMX : Thermal expansion coefficient for volume shifts............................................................................................... 270
TITLE : Specify run title ................................................................................................................................................... 271
TLOW : Define lowest temperature for VFP tables ............................................................................................................ 272
TREF : Specify reference temperatures............................................................................................................................ 273
UNITS : Specify unit conventions..................................................................................................................................... 274
VAR : Specify regression variables ................................................................................................................................... 275
VCRIT : Specify volumes.................................................................................................................................................. 278
VCRITVIS : Specify volumes for LBC viscosity calculations ........................................................................................... 279
VERSION : Version of PVTi .............................................................................................................................................. 280
VFP : Start of the VFP section .......................................................................................................................................... 281
WAT100 : Output water properties .................................................................................................................................... 282
WAT200 : Output water properties .................................................................................................................................... 283
WAT300 : Output water properties .................................................................................................................................... 284
WATVFP : Output water properties .................................................................................................................................... 285
WETGAS : Wet gas tables.................................................................................................................................................. 286
WHIT : Defines Whitson splitting....................................................................................................................................... 287
WHITSON : Blackoil tables ................................................................................................................................................ 288
X/YMFVP: XMFVP and YMFVP ECLIPSE tables .............................................................................................................. 289
ZCRIT : Specify critical Z-factors...................................................................................................................................... 290
ZCRITVIS : Specify critical Z-factors for LBC calculations.............................................................................................. 291
ZI : Specify sample composition...................................................................................................................................... 292
ZMFVD : Composition versus depth table ......................................................................................................................... 293
Chapter 8 - Technical Description ............................................................................................... 294
Overview............. ...............................................................................................................................................................294
PVTi Reference Manual
Table of Contents
5
Theoretical background of PVT ..........................................................................................................................................295
Equation of state. ...............................................................................................................................................................316
Basic laboratory experiments..............................................................................................................................................338
Regression ......... ...............................................................................................................................................................347
Output for ECLIPSE simulators ..........................................................................................................................................353
Analysis techniques ............................................................................................................................................................371
Recommended PVT analysis for oil reservoirs...................................................................................................................372
Recommended PVT analysis for gas condensate reservoirs .............................................................................................377
Consistency tests and correlations .....................................................................................................................................381
Fluid Properties Estimation.................................................................................................................................................384
Regression in PVT analysis................................................................................................................................................386
Wax and asphaltene precipitation in PVTi ..........................................................................................................................394
Cleaning samples contaminated with oil-based mud..........................................................................................................398
Mixing and recombination of samples.................................................................................................................................400
ECLIPSE Thermal Export Module ......................................................................................................................................401
Appendix A - Units........................................................................................................................ 409
Units.................... ...............................................................................................................................................................409
Appendix B - Symbols.................................................................................................................. 413
Symbols .............. ...............................................................................................................................................................413
Appendix C - Bibliography........................................................................................................... 415
Appendix D - Index ....................................................................................................................... 421
6
PVTi Reference Manual
Table of Contents
List of Figures
Figure 5.1 ..........
Figure 5.2 ..........
Figure 5.3 ..........
Figure 5.4 ..........
Figure 5.5 ..........
Figure 5.6 ..........
Figure 5.7 ..........
Figure 5.8 ..........
Figure 5.9 ..........
Figure 5.10 ........
Figure 5.11 ........
Figure 5.12 ........
Figure 6.1 ..........
Figure 6.2 ..........
Figure 6.3 ..........
Figure 6.4 ..........
Figure 6.5 ..........
Figure 6.6 ..........
Figure 6.7 ..........
Fingerprint Plot .......................................................................................................................................40
Phase Plot ..............................................................................................................................................41
The plotted simulation results .................................................................................................................46
Plot of Oil FVF, Viscosity and Rs versus pressure for the output black oil property tables ....................56
Phase Diagram for Schrader Bluff Fluids ...............................................................................................70
The phase envelope plot. .......................................................................................................................78
The main display shows messages indicating the quality of the data.....................................................79
The main plot window after zooming in ..................................................................................................80
The plot of k values versus pressure. .....................................................................................................81
The Hoffman-Crump plot ........................................................................................................................82
Hoffman-Crump-Hocott plot. ...................................................................................................................83
The original sample, the cleaned sample and the estimated contaminant.............................................85
The main PVTi window ...........................................................................................................................91
Fingerprint Plot .....................................................................................................................................109
Phase plot.............................................................................................................................................110
Ternary Plot .........................................................................................................................................111
Main display after performing material balance ....................................................................................113
COMB module - vapor versus pressure plot ........................................................................................114
The VFP module...................................................................................................................................138
PVTi Reference Manual
List of Figures
7
List of Tables
Table 5.1
Table 5.2
Table 5.3
Table 5.4
Table 5.5
Table 6.1
Table 6.2
Table 6.3
Table 6.4
Table 6.5
Table 6.6
Table 6.7
Table 6.8
Table 6.9
Table 6.10
Table 6.11
Table 6.12
Table 6.13
Table 6.14
Table 6.15
Table 6.16
Table 6.17
Table 7.1
Table 7.2
Table 7.3
Table 7.4
Table 7.5
Table 7.6
Table 7.7
Table 7.8
Table 8.1
Table 8.2
Table 8.3
Table 8.4
Table 8.5
Table 8.6
Table 8.7
Table 8.8
Table 8.9
Table 8.10
Table 8.11
Table 8.12
Table A.1
Table A.2
Table A.3
8
The Fundamentals panel .........................................................................................................................35
Component and fluid definitions...............................................................................................................37
Program Options data ..............................................................................................................................39
Constant Composition Expansion experiment at 220o F (* indicates bubble point pressure)..................44
Differential Liberation Experiment at 220o F (* indicates bubble point pressure).....................................47
List of library components ........................................................................................................................95
Observation data....................................................................................................................................123
Set PVTi Program Options panel...........................................................................................................145
Keywords for introducing sections .........................................................................................................156
RUNSPEC keywords .............................................................................................................................156
SYSTEM keywords ................................................................................................................................157
SPLIT keywords.....................................................................................................................................158
GROUP keywords.................................................................................................................................. 159
COMB keywords ....................................................................................................................................159
SIMULATE keywords.............................................................................................................................160
REGRESS keywords .............................................................................................................................160
BLACKOIL keywords .............................................................................................................................161
PSEUCOMP keywords ..........................................................................................................................162
OUTECL3 keywords ..............................................................................................................................162
VFP keywords........................................................................................................................................163
APITRACK keywords.............................................................................................................................163
Error codes ............................................................................................................................................165
Output indices ........................................................................................................................................185
Output indices ........................................................................................................................................186
Required data for experiments...............................................................................................................195
Keyword arguments ...............................................................................................................................196
Restrictions for EXP keyword arguments...............................................................................................198
Component Types..................................................................................................................................211
Equation of State omega values ............................................................................................................237
Default limits for variables......................................................................................................................276
Alkanes ..................................................................................................................................................297
Napthenes..............................................................................................................................................298
Aromatics ...............................................................................................................................................298
Physical properties.................................................................................................................................299
Multi-component (ii) mixtures.................................................................................................................299
CVD Report............................................................................................................................................308
Equation of State coefficients ................................................................................................................318
Equation of State constants ...................................................................................................................319
Parameter estimation data. N is the number of experimental points .....................................................335
Parameter Values for Pure Component Viscosity Correlation ...............................................................335
Physical Properties of Methane and Decane.........................................................................................336
PVTi defaults for Fluid Property Estimation ...........................................................................................385
Units.......................................................................................................................................................410
Constants...............................................................................................................................................411
Conversion factors .................................................................................................................................411
PVTi Reference Manual
List of Tables
New developments
Chapter 1
Developments for 2007.1
Maintenance of this application is continuing until further notice.
PVTi Reference Manual
New developments
Developments for 2007.1
9
Developments for 2005A
Maintenance of this application is continuing until further notice.
10
New developments
Developments for 2005A
PVTi Reference Manual
Developments for 2004A
ECLIPSE Thermal Export facility
For the 2003A version of PVTi a new ECLIPSE Thermal support module was available where
you were able to interactively develop a correlation which accurately predicted K-values for
each component in a given fluid. For the 2004A version this module has been extended to a full
export facility where you can write out files that are suitable for use as PVT input for ECLIPSE
Thermal. The motivation behind this is so that, just as you can export files to use as PVT input
for ECLIPSE BlackOil and ECLIPSE Compositional, they will now be able to do the same for
ECLIPSE Thermal.
PVTi will export a series of keywords when an export for ECLIPSE Thermal is performed. For
a workflow description and brief summary of these keywords see "Compositional Data for
ECLIPSE Thermal" on page 367. For a more technical outline of how the exported keywords
are used in ECLIPSE Thermal see "ECLIPSE Thermal Export Module" on page 401.
Export for API Tracking option in ECLIPSE
BlackOil
The API Tracking facility enables ECLIPSE BlackOil to model the mixing of different types of
oil, having different surface densities and PVT properties.
Without the API Tracking facility, the presence of different types of oil in the reservoir could be
handled with the aid of PVT region numbers. Oil in PVT region 1 would have its properties
determined from PVT table number 1, and so on. However, this method cannot model the
mixing of oil types. Oil flowing from region 1 into region 2 would appear to take on the
properties associated with region 2.
The API Tracking facility essentially replaces the concept of PVT regions for oil. The PVT
tables used for determining the oil properties are selected at each time step according to the
average API of the oil in each grid block (or to be more precise, its average surface density).
For a overview of the workflow involved to export PVT tables suitable for use in ECLIPSE
BlackOil with the API Tracking option turned on see "Export for API Tracking option in
ECLIPSE BlackOil" on page 134. For a more technical description of the API Tracking model
in ECLIPSE as well as an explanation of how PVTi calculates suitable PVT tables see "Model
for API Tracking option in ECLIPSE BlackOil" on page 364.
Batch Mode
For the 2004A version of PVTi the batch mode has undergone a significant revamp. Over the
last few years the user interface of PVTi has evolved rapidly and the existing batch mode facility
no longer adequately supports more recent functionality. There have been 3 significant
modifications to the PVTi batch mode:
1
PVTi Reference Manual
The way a batch mode is executed has changed. The new way to launch a batch mode run
on a PC is to use the command $pvti -batch filename where filename is the
name of your PVTi project. See "General information" on page 152 for more details on
running batch mode with other platforms.
New developments
Developments for 2004A
11
If one of these experiments is selected then in the Experiment List column a list of all the names
of the experiments of that type in your project appears for example, BUBBLE5, DEW3, DL1.
If one of these is selected then all the possible observations available within PVTi for that type
of experiment are displayed in the Observation Type column. Again observation types with a
* next to them means that there are values already defined for this particular experiment in your
project. Simply click on one to see and edit the values. To create a new observation select the
one you want and then click on the + button on the top left of the panel. Values and weights can
then be entered for the observation.
Note
Currently defined observations for an experiment can be edited in the Observations
folder on the experiment Entry panel.
For more information on creating and editing experiments/observations see "Simulation using
PVTi" on page 117 and/or the tutorial "Simulating experiments" on page 43.
What are the data limitations in PVTi?
Pre-2003A
Up to and including the 2002A_1 release (pre-2003A) the following data constraints were
present in PVTi:
•
50 fluid samples
•
50 components per fluid sample* (see below)
•
50 experiments per fluid sample
•
300 observations per experiment
Note
*When a splitting operation was performed it was possible to have more than 50
components (up to 100 in fact) but the components had to be grouped back so that there
were less than 50 before any experiment simulation could take place.
2003A
These pre-2003A data constraints have been present in PVTi for 4 to 5 years and, in-line with
the huge increase in computing power in the last few years, we have decided to enhance the data
constraint capability of PVTi so that the following is now available:
•
100 fluid samples
•
100 components per fluid sample* (see below)
•
100 experiments per fluid sample
•
300 observations per experiment
Note
18
It is now possible to read in, save, split and group with fluids containing up to 100
components. However, the limit is still 50 components for any functionality involving
the EoS flash.
The Most Asked Questions About PVTi
Introduction
PVTi Reference Manual
What is the Fluid Properties Estimation facility in
PVTi?
The Fluid Properties Estimation (FPE) facility in PVTi is designed so that it can be used when
you have minimal data at your disposal, at the well-site for example. In this scenario, a full lab
analysis of multiple fluid samples from the reservoir has not yet been performed. Typically, just
a single sample would be available and minimal fluid behavior known for example, saturation
pressure at a particular temperature.
Specifically, the FPE facility assumes that a single fluid sample with compositional information
is available which includes a single plus fraction (for example C7+) component of which the
weight fraction is known. Typically, this weight fraction data is fairly accurate but the mole
weight, which is used to characterize the critical properties of the plus fraction, is not. The FPE
functionality allows you to perform a quick look simulation that regresses on the mole weight
of the plus fraction, and keep the weight fraction constant, in order to fit to a saturation pressure
observation at a particular temperature.
The FPE facility is available in the top right-hand corner of the fundamentals panel whenever a
new project is created. Alternatively it can be accessed using the Edit | Properties Estimation
(FPE)... option. For more information on this facility see "Fluid Properties Estimation" on
page 384. For an example of how it works see the tutorial "Fluid Properties Estimation" on
page 34.
How do I perform regression on multiple fluid
samples?
General
The fluid samples that PVTi performs regression on is determined by the structure of the tree
view on the left-hand side. By default, PVTi performs a regression on every experiment which
has observations defined, even if there are multiple fluid samples, each with their own
experiments. The reason for this is that, within a project, all fluid samples are considered to be
relevant to each other and so the same fluid model should be applied to all samples, even if the
compositional make-up of each sample is different
Note
If two of your fluid samples are not relevant to each other for example they come from
different wells/reservoirs then a separate project should be created for each one.
Disabling Experiments/Observations
You can prevent PVTi from including an experiment in the regression by right-clicking on the
experiment and selecting Don’t use in Regression. A cross appears on the experiment
indicating it is not currently available within the regression facility.
You can disable an observation so that it is not used within the regression by again right-clicking
and selecting Don’t use in Regression. Alternatively, by right-clicking and selecting Set
Weight and then entering zero the observation is also not included in the regression.
PVTi Reference Manual
The Most Asked Questions About PVTi
Introduction
19
Note
If an experiment is disabled then, as you would expect, all the observations are
automatically disabled.
Regression Weights
In general there will be a set of values in an observation. For example, if we have a differential
liberation (DL) experiment defined then a viscosity observation would have a value for each
pressure. We have two types of weight: there are single weights for each value of an observation
and global weights that apply to every value in an observation.
By right clicking on an experiment observation the global weight can be set. As mentioned
above, by setting this to zero none of the values in the observation would be used. Alternatively,
you may want to set a global weight for an experimental observation particularly high, for
example, matching the bubble point of a fluid is normally very important if one wants to ensure
that it is a single-phase liquid at the temperature and pressure of the reservoir.
Or maybe you do not trust the accuracy of a particular observation value, for example an oil
formation volume factor (FVF) value in a DL experiment.You may then not want to use a global
weight as all the other observation values look ok. In this case setting a single-value weight to
a very low value helps you match all the other values in the observation during regression as the
rogue, inaccurate value no longer inhibits convergence.
Both the single-value and global weights for an experimental observation can be set in the
Observations panel by selecting the Edit | Observations... option, highlighting the
appropriate observation and then simply typing in your chosen weights.
For a good example of how to use the regression facility, see the tutorial "Fitting an equation of
state to experimental results" on page 50.
What is the difference between normal regression,
special regression and automatic (PVTi selects)
regression?
There are 3 types of regression: normal, special and automatic. The difference between them
depends entirely on what kind of variables are being regressed on.
Normal regression parameters are equation of state variables relating to a particular component,
for example, critical pressure, Pc , critical temperature, T c , acentric factor, ω . and the binary
coefficients. The full set of normal regression variables can be viewed using the regression
panel using the Run | Regression... panel. Select normal as the regression type and then click
variables - the upper table shows the single-valued normal regression parameters for each
component and the lower panel shows the binary coefficients table. For more information on
setting normal regression see "Setting normal variables" on page 127.
Special regression parameters are global Equation of State variables, for example, the thermal
expansion coefficient or the Cheuh-Prausnitz A factor for binary coefficients. There may also
be some splitting parameters available as special regression variables depending on whether a
multi-feed split has been performed on the plus fraction. See "Multi-feed Split (also called semicontinuous thermodynamic (SCT) split)" on page 106 for more details on this facility. For more
information on setting special regression variables see "Setting special variables" on page 129.
20
The Most Asked Questions About PVTi
Introduction
PVTi Reference Manual
PVTi should then write the tables to a file and show them in the output display. This file is then
suitable to use as the PVT input for an API Tracking run in ECLIPSE BlackOil. For a similar
description of the API Tracking workflow see "Export for API Tracking option in ECLIPSE
BlackOil" on page 134. For a technical description of the API Tracking model in ECLIPSE as
well as an explanation of how PVTi calculates suitable PVT tables see "Model for API Tracking
option in ECLIPSE BlackOil" on page 364.
26
The Most Asked Questions About PVTi
Introduction
PVTi Reference Manual
Introduction
Chapter 3
General information
The PVTi program is an Equation of State based package for generating PVT data from the
laboratory analysis of oil and gas samples. The program may be used through an interactive
menu system or run in a batch mode. An interactive session can be saved as a batch input file,
which contains commands to reproduce the interactive operations. Alternatively, a batch input
file can be run from an interactive session.
Equations of state and viscosity correlation
Four equations of state are available, implemented through Martin’s generalized equation. This
enables the Redlich-Kwong, Soave-Redlich-Kwong, Peng-Robinson and Zudkevitch-Joffe
equations to be used. Two 3-parameter extensions of the Peng-Robinson Equation of State are
also available, one based on a Peneloux et al. volume shift, the other being an implementation
of the Schmidt-Wenzel Equation of State 2-parameter Peng-Robinson. The Soave-RedlichKwong Equation of State similarly has a three-parameter extension.
Viscosities may be calculated using a method by Pedersen et al. based upon a corresponding
states comparison with methane, or by the Lohrenz-Bray-Clark method.
Fluid definition
Multiple fluid samples can be defined by specifying components as one of three types. Library
components require only that the appropriate component mnemonic be entered. Characterized
components define properties of plus fractions from a limited set of information. Finally all the
properties of a component can be defined, a facility which can be used selectively to edit the
properties of existing components.
PVTi Reference Manual
Introduction
General information
27
It is possible to group the components to reduce or pseudoise the fluid system (make a fluid
definition of the system using pseudo components), or to split the plus fraction into more
components, preserving molecular weight and mole fraction. Multiple samples having different
plus fraction properties, say mole weight and specific gravity, can be characterized by splitting
the plus fraction into two or more pseudo-components of fixed properties but variable
composition.
Fingerprint plots of mole fraction against molecular weight, or phase diagrams, are available.
Material balance checks
A compositional material balance can be performed on any gas condensate or volatile oil for
which a laboratory constant volume depletion or differential liberation experiment has been
performed. This can be used to estimate liquid compositions and hence K-values. The calculated
quantities can then be used to estimate the quality and consistency of the laboratory data.
Additionally, tests on recombination of separator data can be performed and estimates of
reservoir recovery can be made.
Simulation of experiments
Experiments may be performed on the fluid systems defined using the equation of state model.
Possibilities are:
•
saturation pressures
•
flash calculations
•
constant composition expansions
•
constant volume depletions
•
differential liberations
•
swelling tests
•
multi-stage separator simulations.
Other experiments available are:
28
•
composition versus depth
•
vaporization test
•
multiphase flash
•
critical point
•
saturation temperature
•
first contact miscibility
•
multiple contact miscibility (condensing and vaporizing).
•
wax appearance temperature
•
asphaltene appearance pressure
Introduction
General information
PVTi Reference Manual
Regression of equation-of-state to measured data
The equation of state model may be tuned by regression. The critical state data, Ωa and Ω b
values, interaction coefficients, δ ij , and volume shift parameters,
si
(for the three-parameter
volume shift equations of state), may be matched to experimental data from the first eight of the
experiments mentioned in the previous paragraph. Additionally, depending on the use of certain
facilities and options, five special regression parameters are also available. These are the A
coefficient in the Cheuh-Prausnitz Bids, the thermal expansion coefficient in the modified
Peneloux et al. volume shift method, and three variables associated with the Modified Whitson
splitting technique (denoted Semi-Continuous-Thermodynamics), being the mole weight and
distribution skewness parameter (on a sample-by-sample basis) and the characterization factor
of the plus fraction.
Hint
Almost any result from the experiments mentioned can be used as an observation
against which to regress.
PVT data for ECLIPSE simulators
Black oil and equilibration tables for ECLIPSE can be prepared, using the liquid and gas
compositions obtained from constant volume depletion or differential liberation experiments
passed through a separator system using the Coats or Whitson and Torp methods.
Gas injection schemes can be modeled using the ECLIPSE pseudo-compositional model which
modifies the ECLIPSE black oil tables as a function of the volume of injected gas.
For use in ECLIPSE Compositional, either pseudoised/regressed equation of state data or
tabular data (either K-values or liquid and vapor mole fractions as a function of pressure) can
be output.
Black oil tables can also be generated for the Vertical Flow Performance (VFPi) program,
simulating the phase and volumetric change in the wellstream fluid by a constant composition
expansion experiment at two temperatures, the highest (reservoir) and lowest in the production
string.
Water properties may also be output for use in any of the above programs. Default values for
formation volume factor, compressibility, etc., are constructed using well-known correlations
from specification of the pressure, temperature, salt and gas content of the water, though these
may be changed.
PVTi Reference Manual
Introduction
General information
29
30
Introduction
General information
PVTi Reference Manual
Getting started
Chapter 4
Starting PVTi
Windows platforms
ECLIPSE Program Launcher
1
Start the ECLIPSE Program Launcher.
2
Click on the PVTi button.
3
Select the version and working directories as required.
Command line
1
Type the command $PVTI in a command prompt window.
UNIX platforms
1
PVTi Reference Manual
Type the command @pvti at the command prompt.
Getting started
Starting PVTi
31
Tutorials
Chapter 5
Overview
The tutorials provide a step-by-step introduction to the functionality of PVTi.
Note
These tutorials are not intended to teach PVT analysis, but instead concentrate on
illustrating typical work-flows for PVTi.
Each tutorial is divided into a number of distinct sections intended to highlight a specific aspect
of the analysis process. To avoid repetition, later tutorials assume familiarity with some used in
the first tutorials, so it is strongly recommended that you work through them in the order they
are presented.
Available tutorials
The following tutorials are available:
•
"Fluid Properties Estimation" on page 34
•
"Creating a fluid system" on page 37.
•
"Simulating experiments" on page 43.
•
"Fitting an equation of state to experimental results" on page 50.
•
"Exporting ECLIPSE Black Oil PVT tables" on page 54.
•
"Converting a black oil run to compositional" on page 58.
•
"Workflow Tutorial" on page 61.
•
"Multiphase Flash" on page 69.
•
"Exporting an ECLIPSE Thermal model" on page 73.
•
"Data analysis and quality control" on page 77.
•
"Removing contamination from samples" on page 84.
PVTi Reference Manual
Tutorials
Overview
32
•
PVTi Reference Manual
"Converting old projects to the current version" on page 87.
Tutorials
Overview
33
Fluid Properties Estimation
This tutorial describes how to use PVTi for Fluid Properties Estimation.
The data for this tutorial is provided with the standard installation of PVTi in the directory:
$ECL/2007.1/pvti/tutorials
and you should copy the files from this directory to your local directory before starting the
tutorial.
The tutorial is split into several sections:
•
"Introduction" on page 34
•
"Basic Information - Fundamentals" on page 34
•
"Flash calculations" on page 36
•
"Discussion" on page 36
Introduction
Fluid properties estimation can provide quick-look PVT tables at the well site.
A saturation pressure (bubble or dew-point) together with a reservoir composition are sufficient
inputs to provide a quick-look simulation, giving an initial estimation of fluid properties in
advance of a full fluid analysis in the lab.
After completing this tutorial you should be able to use PVTi as a simulation tool for fluid
properties estimation.
Basic Information - Fundamentals
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
Enter FPE.PVI as the file name for the new project.
Hint
When a new, empty project is created in PVTi, the Fundamentals panel opens
automatically. To re-enter this panel at any later time, select PVTi: Edit |
Fundamentals...
The Fundamentals panel allows you to enter the minimum information required to create
a complete equation of state model.
3
Click on the Enter Weight Fractions check box.
Hint
34
The mole fractions that you see in lab reports are derived from weight fractions and the
mole weights of the components. It is weight fractions that are actually measured.
PVTi allows a choice of either form in the Fundamentals panel.
Tutorials
Fluid Properties Estimation
PVTi Reference Manual
4
Right-click in the table and select Table Import | From File.
a
Import the file FUNDAMENTALS.TXT .
b
In the Text Import Wizard switch on Ignore Records and set the number of records
to ignore to 2 (since we want to ignore the column headings).
The Fundamentals panel should now look like Table 5.1.
Table 5.1
Components
The Fundamentals panel
ZI
Weight Frac.
(percent)
(percent)
CO2
0.43
N2
0.05
C1
6.25
C2
3.10
C3
3.27
IC4
0.89
NC4
2.44
IC5
1.11
NC5
1.09
C6
3.88
C7+
77.49
Hint
5
Mol Weight
Spec Gravity
218
Only enter mole weights for components whose properties will be characterized, the
other components come from the library. Also, specific gravity is an optional
additional parameter that can be used in the characterization, if it is not specified it is
calculated using a correlation.
Click Apply
PVTi adds the mole fractions and the specific gravity of the plus fraction.
6
Click on the Fluid Properties Estimation (FPE) check box
The temperature and pressure fields are now active.
a
Enter a Temperature of 220 F.
This is the temperature of the saturation pressure (dew or bubble point) and the
temperature that is used in the generated depletion experiments.
b
Hint
c
PVTi Reference Manual
Enter a Saturation Pressure of 2800 psia.
PVTi uses this saturation pressure to fit the fluid model. The weight of the plus-fraction
is varied, the weight fraction being constant, until the saturation pressure predicted by
the equation of state matches the entered pressure.
Enter a Maximum Pressure of 5000 psia.
Tutorials
Fluid Properties Estimation
35
Hint
This is the maximum pressure in the depletion experiments that are created.
7
Set the Project Units to Field, this sets the units that are used on the plots.
8
Click OK.
This is all the information required to fit the equation of state and to generate the Constant
Composition Expansion (CCE), depletion experiment (either differential liberation or constant
volume depletion) and the optimized separator. After fitting the equation-of-state and creating
the experiments, default plots from the depletion experiments are drawn along with the phase
curve for the fitted fluid.
The methods used in Fluid Properties Estimation are explained in "Fluid Properties Estimation"
on page 384.
9
PVTi: Run | Simulate
This opens a complete report for the project including the results from all the created
experiments.
Hint
By clicking on one of the experiments in the sample tree with the right mouse button,
and selecting Report..., you can view the reports for individual experiments
separately.
Flash calculations
1
2
Right-click on ZI in the project tree-view and select Properties Estimation (FPE)...
a
Enter a temperature of 60 F
b
Enter a pressure of 15 psia
c
Click OK.
Right-click on the newly created Flash simulation (FLASH1) and select Report to see the
results of flashing the reservoir fluid to standard conditions.
This allows you to attempt any Flash calculation on the reservoir fluid.
Hint
The Properties Estimation panel can also be used to create additional separators,
saturation pressure or depletion experiments, for example at other temperatures.
Discussion
Fluid Properties Estimation is a useful tool, particularly in situations where full lab analysis of
the fluid is not available for a complete equation-of-state matching project.
For full details of the operations performed during fluid property estimation see "Fluid
Properties Estimation" on page 384.
During fluid properties estimation, the project created is a complete PVTi project. This means
that a more experienced user has access to the rich range of features within the product. At the
same time, the less experienced user can use PVTi for Fluid Properties Estimation without
requiring in-depth knowledge of equation-of-state methods or PVT analysis.
36
Tutorials
Fluid Properties Estimation
PVTi Reference Manual
Creating a fluid system
This tutorial describes how to specify fluid properties in PVTi. It covers the basic functionality
of PVTi; knowledge of this tutorial is assumed in the later tutorials, so you are advised to work
through them in order.
The data for this tutorial is provided with the standard installation of PVTi in the directory:
$ECL/2007.1/pvti/tutorials
and you should copy the files from this directory to your local directory before starting the
tutorial.
The tutorial is split into several sections:
•
"Introduction" on page 37
•
"Defining a fluid" on page 37
•
"Selecting an equation of state" on page 39
•
"Program options" on page 39
•
"View fluid attributes" on page 40
•
"Saving the SYSTEM section for future use" on page 41
•
"Discussion" on page 42
Introduction
The PVT report for this fluid contains details of three experiments: a Constant Composition
Expansion experiment, a Differential Liberation experiment, and a Bubble Point experiment.
The later tutorials describe how the experimental results may be used to fit an equation of state
to the experimental behavior, and how this fitted equation of state can be used to generate PVT
tables for use in reservoir simulations.
This tutorial shows how to set up basic fluid properties in PVTi and how to display the phase
envelope for the defined fluid.
Defining a fluid
PVT analysis involves fitting an Equation of State to experimental data and then using this
Equation of State to produce PVT tables for use in reservoir simulations. The first step is to start
up PVTi, and import the component and fluid definitions.
Table 5.2 shows the component and fluid definitions that are used in this tutorial.
Table 5.2
PVTi Reference Manual
Component and fluid definitions
Component
% Mole Fraction
CO2
0.91
N2
0.16
C1
36.47
Mole Weight
Specific Gravity
Tutorials
Creating a fluid system
37
Table 5.2
Component and fluid definitions
Component
% Mole Fraction
C2
9.67
C3
6.95
IC4
1.44
NC4
3.93
IC5
1.44
NC5
1.41
C6
4.33
C7+
33.29
Mole Weight
Specific Gravity
218.0
0.8515
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
Select PVTi: File | New...
3
Enter BLACK.PVI as the project name in the file selection window.
4
Click on Open on PC or OK on UNIX platforms.
Note
This has defined BLACK as the prefix for any files that are written by PVTi.
The Fundamentals panel opens so that basic project information can be entered.
38
1
Enter CO2, N2, C1 and C6 into the Components column.
2
Click Apply.
3
Click Yes so that PVTi fills in the library component names.
4
Enter the mole fractions from Table 5.2 and the details for the C7+ component into the
Fundamentals panel and click OK.
Note
The components for which no mole weight or specific gravity has been specified are
automatically set to use the PVTi component properties library (see "Component
types" on page 102.)
Hint
The component properties can be examined by selecting PVTi: Edit | Fluid Model |
Components.... This panel can also be used to add additional components, the select
alternative characterization methods and to manually defined component properties.
Hint
Only one sample, ZI, is defined in the Fundamentals panel. Additional samples can
be created using PVTi: Edit | Samples | Names... and mole fractions can be entered
using PVTi: Edit | Samples | Compositions...
Tutorials
Creating a fluid system
PVTi Reference Manual
Selecting an equation of state
In this tutorial, the three-parameter Soave-Redlich-Kwong equation of state (see "Equation of
state formulation" on page 317) is fitted to the results of experiments carried out on the fluid
defined in "Defining a fluid" on page 37. The Lohrenz-Bray-Clark correlations (see "Lohrenz,
Bray and Clark" on page 330) is used for viscosity.
1
PVTi: Edit | Fluid Model | Equation Of State...
This opens the Equation of State and Viscosity Correlation panel.
2
Select the 3-parameter Soave-Redlich-Kwong equation of state (SRK3).
3
Click on OK.
4
Click on OK to change the parameters to SRK3 defaults.
Program options
1
PVTi: Utilities | Program | Options...
This opens the Program Options panel.
2
Set the Separator GOR calculation to use Liquid at Stock Tank Conditions.
3
Set the Temperature-dependence for volume shifts to be calculated by Polynomial
correlations. (See "Shift parameters" on page 321.)
The Program Options panel should now contain the following data:
Table 5.3
Program Options data
Field
Data
Definition of Liquid Saturation in CCE
Sliq=Vliq/Vsat
Treatment of volume shifts
Dependent
Separator GOR Calculation
Liquid at Stock Tank Conditions
Temperature dependence for volume shifts
Polynomial correlations
Specify/Calculate density and molar volume units
User units
Specific Heat Capacity Coefficients and Calorific Values
PVTi Reference Manual
Calculated compositions
No Save to samples
Component Library
Katz-Firoozabadi
Experimental Compositions
Output to Screen/PVP
Experimental Results
Always Output to PVP
Plot Vectors
No Output to file
Print File Output
A4 format
Definition of GOR in Diff Lib
Normal
Definition of Oil relative volume in Diff Lib
Oil FVF = Voil(p)/Voil(stc)
Black Oil Table Output
All Data
Flash Calculations
E300 Flash
Sample mole fractions when regressing
Keep Fixed
Tutorials
Creating a fluid system
39
4
Set Treatment of Volume Shifts to Independent and click on OK.
View fluid attributes
Now that a fluid has been defined, there are two plots available to review the fluid we have
entered. First is the fingerprint plot of mole fraction versus molecular weight; the second is a
phase plot.
1
Right-click on ZI in the project tree-view and select Fingerprint Plot from the pop-up
menu.
The plot should look like Figure 5.1.
Figure 5.1 Fingerprint Plot
40
2
PVTi: View | Samples | Phase Plot...
3
Request Sample ZI, 5 quality lines.
4
Click on OK.
The plot should look like Figure 5.2.
Tutorials
Creating a fluid system
PVTi Reference Manual
Figure 5.2 Phase Plot
Note
A default phase plot with a single quality line can be generated by dragging ZI from
the tree-view of the project (in the left pane of the main window), and dropping it on
to the main plot workspace.
Saving the SYSTEM section for future use
The fluid sample definition can output as the RUNSPEC and SYSTEM sections of a PVI file.
1
PVTi: File | Save (Concise)...
2
Call the file FLUID_DEF.PVI.
Hint
The complete project can be saved using PVTi: File | Save... This, effectively, saves
a history of the project. The original fluid description is saved, along with SPLIT or
GROUP sections for split and group operations you perform. By choosing to save
current modifications, the system is saved in its current state, after all splits, groups,
etc., have been performed. For work in progress it is usually better to use Save so that
past steps can be recovered. For a final fluid model, the Save (Concise) option allows
a complete description of the final model to be saved, without the steps taken to get
there.
This file can now be read in using the PVTi: File | Import | SYSTEM... option.
PVTi Reference Manual
Tutorials
Creating a fluid system
41
Discussion
In this tutorial a fluid was defined from data and an Equation of State was selected to describe
that fluid. This fluid definition provides the basic building blocks for further PVT analysis. The
fluid definition can be used in simulation studies to compare it with experimental results from
the reservoir fluid; see "Simulating experiments" on page 43. This definition can then be
adjusted so that it describes the experimental results; see "Fitting an equation of state to
experimental results" on page 50. The fitted fluid definition is finally used to generate PVT
tables for ECLIPSE ; see "Exporting ECLIPSE Black Oil PVT tables" on page 54, ECLIPSE
pseudo-compositional, VFPi and ECLIPSE Compositional.
42
Tutorials
Creating a fluid system
PVTi Reference Manual
Simulating experiments
This tutorial illustrates how experiments are simulated in PVTi. It covers the basic functionality
of PVTi. Knowledge of this tutorial is assumed in later tutorials, so you are advised to work
through them in order. The data for this project are provided in the standard installation of PVTi
in the directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
The tutorial is split into several sections:
•
"Introduction" on page 43
•
"Defining experiments for simulation" on page 44
•
"Plotting simulation results" on page 46
•
"Defining further experiments and observations" on page 46
•
"Defining further experiments and observations" on page 46
•
"Simulating all the experiments" on page 48
•
"Discussion" on page 49.
Introduction
This tutorial describes how experimental observations can be entered into PVTi and how the
experiments can then be simulated from an existing fluid definition.
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
File | Open...
3
Open the file FLUID_DEF.PVI that was created in the last tutorial. (Alternatively open
the supplied tutorial file FLUID_CORRECT.PVI).
Setting units
1
Utilities | Units...
2
Set the Unit Type to Field
3
Set the Temperature Unit Type to Fahrenheit
4
Set Mole Fraction or Percentage to Percentage
5
Set Absolute or Gauge Pressure to Gauge.
6
Click on OK.
PVTi Reference Manual
Tutorials
Simulating experiments
43
Defining experiments for simulation
In this part of the tutorial, the experimental results from the PVT report are brought into PVTi
ready for simulation. In this section data from a constant composition expansion experiment are
brought into PVTi. If you do not have access to a spreadsheet, type the numbers from the tables
into the data entry forms in PVTi at the appropriate points.
Table 5.4
44
Constant Composition Expansion experiment at 220 o F (* indicates
bubble point pressure)
Pressure
Relative Volume
(PSIG)
(V(p)/V(pb)
5000.0
0.9453
4500.0
0.9541
4000.0
0.9638
3500.0
0.9746
3000.0
0.9867
2900.0
0.9893
2800.0
0.9920
2700.0
0.9948
2620
0.9970
2605
0.9974
2591
0.9978
2516.7*
1.0000
2401
1.0243
2253
1.0599
2090
1.1066
1897
1.1750
1698
1.2655
1477
1.4006
1292
1.5557
1040
1.8696
830
2.2956
640
2.9457
472
3.9877
1
PVTi: Edit | Experiments...
2
Experiment Entry: Add | Pressure Depletion | Constant Composition Expansion...
Tutorials
Simulating experiments
PVTi Reference Manual
Hint
The constant composition expansion or CCE experiment can sometimes be known as
a constant mass study in PVT Reports.
The differential liberation or DL experiment is also known as a differential
vaporization experiment in PVT Reports.
The multi-stage separator or SEPS experiments can also be called a separation test in
PVT Reports.
The Experiment Entry window now shows three folders: General, Observations and
Components. These folders are used to define the experiment entry form.
3
Select the Observations folder.
4
Click in the top left cell of the table and select Pressure from the drop-down list in that
cell.
5
In the second column select Relative Vol. from the drop-down list.
Hint
6
By making the column headings the same as those in Table 5.4, the task of data entry
is simplified. The ability to tailor the table means that data entry can then be further
accelerated by importing observations from a text file or the clipboard.
Click on Next.
The table now shows two folders. The Components folder has disappeared as there were
no component observations selected; the General folder now shows an entry field to select
fluid type and another to enter the temperature of the experiment.
7
In the General folder, enter the temperature from Table 5.4 (220 F).
8
Select the Observations folder.
The Observations folder now shows a two-column table with the columns selected
previously. The table resembles Table 5.4.
Table 5.4 is provided in the file CCE_TABLE.TXT
9
Right-click in the table and select Table Import | From file...
10 Select CCE_TABLE.TXT and click on Open.
11 In the Text Import Wizard turn on Ignore Records and set the number of records to ignore
to 1 (since we want to ignore the column headings).
The view of the table should no longer contain the first row.
12 Click on OK.
Note
The error message “Cannot delete rows from this table” appears This
is because the table has a fixed length and the file we are importing from has fewer
rows than the table. This message can be safely ignored.
13 Click on OK to remove the message “Cannot delete rows from this table”.
The table now contains the same information as Table 5.4. As the experiment information
is complete, the experiment can be created.
14 Click on Next to create the experiment.
PVTi Reference Manual
Tutorials
Simulating experiments
45
Hint
The data tree now shows the created experiment (CCE1). The asterisk (*) next to the
experiment’s name means that it is active. CCE1 has one observation node, for the
relative volume measurements.
15 Click Close to shut the panel.
Plotting simulation results
1
Click on the Relative Vol. observation in the Data Tree and drop it over the Main Plot
Window.
The Main Plot Window should now look like Figure 5.3.
Figure 5.3 The plotted simulation results
Defining further experiments and observations
In this section of the tutorial the other experiments are defined, along with their observations.
The equation of state is later fitted to these observations, and then the fitted equation is used to
generate tables for a fully compositional ECLIPSE simulation.
46
Tutorials
Simulating experiments
PVTi Reference Manual
Differential liberation experiment
The first experiment to be added is a differential liberation experiment (Table 5.5), as in
"Defining experiments for simulation" on page 44.
Table 5.5
Differential Liberation Experiment at 220o F (* indicates bubble point
pressure)
Gas
Deviation
Factor
Z
Reservoir
Oil
Density
Solution
GOR
(Mscf/stb)
2516.7*
1.7493
1.1342
2350
1.7095
1.0526
0.8686
45.6688
0.7553
1.2574
2100
1.6535
0.9378
0.8692
46.5022
0.7547
1.4070
1850
1.6013
0.8309
0.8719
47.3311
0.7565
1.6006
1600
1.5523
0.7307
0.8767
48.1595
0.7614
1.8586
1350
1.5057
0.6361
0.8836
48.9920
0.7704
2.2164
Pressure
(PSIG)
(lb/ft3)
Gas
Relative
Density
Gas
Volume
Factor
Oil
Volume
Factor
(rb/Mscf)
45.110
1100
1.4609
0.5460
0.8926
49.835
0.7859
2.7411
850
1.4171
0.4591
0.9036
50.6992
0.8121
3.5773
600
1.3726
0.3732
0.9167
51.6076
0.8597
5.1050
350
1.3234
0.2824
0.9324
52.6319
0.9618
8.7518
159
1.2720
0.1960
0.9481
53.6731
1.1726
18.6846
0
1.1228
0.0
56.3229
1.8901
1
PVTi: Edit | Experiments...
2
Experiment Entry: Add | Pressure depletion | Differential Liberation...
3
In the Observations folder, set the table headings to match those in Table 5.5: Pressure,
Oil Rel. Vol., Gas-Oil ratio, Vapor Z-factor, Liquid Density, Gas Gravity, Gas FVF.
4
Click on Next
5
Enter 220 F as the temperature in the General folder.
The file DL_TABLE.TXT provides the table in Table 5.5.
6
Import the file DL_TABLE.TXT into the table in the Observations folder, remembering
to ignore the first line, which contains column headings.
7
Click on Next to create the experiment.
The Experiment Entry panel now shows that there are 2 experiments defined.
Defining the bubble point experiment
Finally, there is a bubble point experiment at 220o F to be added.
1
Experiment Entry: Add | Single Point | Bubble Point...
2
In the Observations folder set the first column heading to Sat. Pressure and the second
to Liquid Density
3
Click on Next
PVTi Reference Manual
Tutorials
Simulating experiments
47
4
Enter the temperature, 220o F in the General folder.
5
Select the Observations folder.
6
Enter the saturation pressure as 2516.7 psig and the liquid density as 45.11 lb/ft3.
7
Click on Next to create the experiment.
8
Click Close.
Simulating all the experiments
All the experiments have now been entered. In summary, then, the project should now contain
the following:
•
A fluid description (component properties and a sample defined by mole fractions of
components).
•
A Constant Composition Expansion experiment with observations of relative volume.
•
A Differential Liberation experiment with observations of: relative oil volume, solution
gas-oil ratio, Z-factors, oil density, gas gravity and gas formation volume factor.
•
A Bubble Point experiment at 220o F with observations of bubble point pressure and liquid
density.
Hint
1
The information about which experiments have been defined, and for which
observations have been entered for those experiments, is contained in the Data Tree.
PVTi: Run | Simulate
A simulation report, showing information on all the experiments, is displayed in the Output
Display panel.
2
Output Display: File | Close
Plotting all observations for an experiment
1
PVTi: View | Observations...
2
Select the Differential Liberation (DL1) experiment.
3
Click OK.
This plots each observed data set (as points) for the differential liberation experiment and
each calculated data set (as lines) generated by simulation.
Hint
4
Examine each of the plots and note how well (or badly) the simulation has matched the
data.
Hint
48
Double-clicking on one of the small plots swaps it with the large plot.
You can right-click on an axis and select Show Edit Box from the drop-down menu.
This opens the Axis Property Editing panel. In this panel you can customize the axes,
for example by changing the units used in plotting.
Tutorials
Simulating experiments
PVTi Reference Manual
In the next section, the match between calculated and observed data values are improved by
regression.
Saving the project for future use
The fluid sample definition can be output as the RUNSPEC, SYSTEM and SIMULATE sections
of a PVI file.
1
PVTi: File | Save (concise)...
2
Call the file SIMULATE_SECTION.PVI .
Discussion
In this tutorial an existing project was extended to include experiments. Constant Composition
Expansion, Bubble Point and Differential Liberation experiments were imported and simulated
for the defined fluid. The match between the experimental observations and the simulated
results was examined using the plotting facilities in PVTi. The fluid model can then be adjusted
so that it provides the best fit (in a least-squares sense) to the experimental observations (see
"Fitting an equation of state to experimental results" on page 50). The fitted fluid definition is
finally used to generate PVT tables for ECLIPSE (see "Exporting ECLIPSE Black Oil PVT
tables" on page 54).
PVTi Reference Manual
Tutorials
Simulating experiments
49
Fitting an equation of state to experimental results
This tutorial shows how a fluid definition can be fitted, by regression, to describe experimental
results. This tutorial covers basic functionality of PVTi and knowledge this tutorial is assumed
in later tutorials, so you are advised to work through them in order. The data for this project are
provided in the standard installation of PVTi under the directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
The tutorial is split into several sections:
•
"Introduction" on page 50
•
"Fitting an equation of state by regression" on page 50
•
"Discussion" on page 53
Introduction
This tutorial illustrates the fitting of the fluid definition to the experimental observations.
The fluid definition and experiments are read in from an existing PVI file and the regression
facilities in PVTi are used to generate an improved fit between the two.
Fitting an equation of state by regression
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
File | Open...
3
Open the file SIMULATE_SECTION.PVI created in the last tutorial. (Alternatively you
can use the file SIMULATE_CORRECT.PVI .)
Hint
The Data Tree shows the contents of the opened project.
Fitting an equation of state by regression
In this part of the tutorial, the equation of state is fitted to the observation data to produce a better
representation of the fluid. A sensitivity analysis is carried out to determine which attributes of
the fluid components improve the solution by the smallest change. The most sensitive attributes
are then adjusted slightly by regression to improve the equation of state model of the fluid.
The first step in designing any regression is to determine the parameter set that will be used.
There are certain steps an engineer can take to improve the performance of a regression. The
first step is to try to make all regression variables have similar sizes. This is done to prevent a
minor constituent of the fluid having its properties varied extensively to achieve a mathematical
fit, which is not a reasonable physical solution.
1
50
Examine the fluid component data in "Component and fluid definitions" on page 37.
Tutorials
Fitting an equation of state to experimental results
PVTi Reference Manual
Note
The idea here is to look for consecutive components that have small mole fractions.
These can be grouped together and treated as a single regression variable, forcing the
solution to be physically realistic.
Hint
The properties of C1 and C2 are well known and generally do not differ significantly
from the library properties.
Grouping the C3, IC4, NC4, IC5, NC5 and C6 components into a single regression variable
preserves monotonicity between the components, in addition to creating a variable that accounts
for 19.5% of the total composition.
Hint
The plus fraction (C7+) contains a mixture of components C7+ and higher, so its
properties may not be so well-determined. This makes the plus fraction an ideal
candidate for regression to fit the equation of state to the experimental results.
C7+ is the second regression variable.
Sensitivity analysis
Sensitivity analysis is used to establish which fluid properties most affect the difference
between the observed and simulated values. The sensitivities are calculated for critical
temperature and pressure for each experiment, for both regression variables. Finally the most
sensitive properties will be selected for use in the regression.
Hint
In any regression, having a few very sensitive parameters is preferable to having
hundreds of insensitive ones. Always look for parameters that can be discarded (this is
called conditioning the problem - an ill-conditioned problem is difficult to solve).
1
PVTi: Run | Regression... opens the Regression panel.
2
Select Normal as the Type of regression variables in the Variables section of the panel.
3
Click Variables.
The regression variables are numbered for each property. Entering 1 in the critical pressure
(Pcrit) column in the rows corresponding to C3, IC4, NC4, IC5, NC5 and C6 groups those
components into the first regression variable.
4
PVTi Reference Manual
Fill in the table in the Select EOS parameters for regression panel with the following
data:
Mnem
Pcrit
Tcrit
C3
1
1
IC4
1
1
NC4
1
1
IC5
1
1
NC5
1
1
C6
1
1
C7+
2
2
Tutorials
Fitting an equation of state to experimental results
51
5
Leave the second part of the Select EOS parameters for regression panel blank.
6
Click on OK.
Hint
7
The second part of the Select EOS parameters for regression panel relates to
binary interaction coefficients.
Click Regression in the Report section of the panel
The Regression Report panel provides several views of the regression problem, designed
to give the best possible insight into creating a fluid model.
For a description of the Regression Report panel see "Regression Report" on page 130.
a
Select the Sensitivities folder.
The sensitivities for the first Pcrit parameter are generally lower than for the other
regression variables.
b
Select the Hessian folder.
The values in the leading diagonal dominate the matrix, except in the first row, the row
relating the first Pcrit parameter.
c
Select the Covariance folder
In this table the largest value is for the first Pcrit parameter, indicating that it is the least
well determined by the regression.
d
Select the Correlation folder.
There is a strong negative correlation between the two Pcrit parameters, indicating that
the regression would proceed better if only one of those two parameters were used.
From an examination of the information in the Regression Report panel, it can be seen
that the first Pcrit parameter is not likely to aid the regression, and it may hinder it.
Consequently that regression variable is removed before regression is started.
8
Close the Regression Report panel.
9
Click Variables in the Regression panel.
10 In the Select EOS parameters for regression panel click on Reset to clear all the cells
in the table.
11 Fill in the columns to describe the reduced set of regression variables with the following
data:
Mnem
Pcrit
Tcrit
C3
1
IC4
1
NC4
1
IC5
1
NC5
1
C6
C7+
1
1
2
12 Click on OK.
52
Tutorials
Fitting an equation of state to experimental results
PVTi Reference Manual
Viewing the regression progress
The results of regression are viewed in a similar way to the results of simulation.
1
Right-click on experiment DL1 in the project tree-view and select Plot from the pop-up
menu.
2
Click Run in the Regress section of the Regression panel.
This starts the regression.
3
Click on Regression in the Report section of the Regression panel.
a
Select the Modifiers folder.
The difference between the final and initial value of each regression variable is
displayed.
b
Select the Details folder.
An observation-by-observation breakdown of the final fit is shown, along with the total
fit to all data (both unweighted and incorporating the observation weights).
4
Examine the plots in the main window.
The observed data are plotted as points and the simulated data before and after regression
are plotted as lines.
The regression has improved the equation of state model, so the regression results can be
accepted.
Hint
Right-clicking on an experiment allows you to choose to turn off that experiment
during the regression process.
5
Click Accept in the Regress section of the Regression Panel.
6
Close the Regression Report panel.
Saving the project
1
PVTi: Save (concise)...
2
Call the file REGRESS_SECTION.PVI
The results of regression are the fluid definition (that is the SYSTEM section) of the newly
created PVI file. They can now be read in using the PVTi: File | Import PVI Section |
SYSTEM... option.
Discussion
In this tutorial a fluid definition, an Equation of State and some experiments along with their
observations were imported from an existing PVI file (the file created in "Simulating
experiments" on page 43). The definition was adjusted so that it provided the best fit (in a leastsquares sense) to the experimental observations ("Fitting an equation of state to experimental
results" on page 50). This fitted fluid definition can now be used to generate PVT tables for
ECLIPSE (see "Exporting ECLIPSE Black Oil PVT tables" on page 54).
PVTi Reference Manual
Tutorials
Fitting an equation of state to experimental results
53
Exporting ECLIPSE Black Oil PVT tables
This tutorial provides a typical workflow for PVTi: producing PVT tables that are then used in
an ECLIPSE BlackOil simulation. The data for this project are provided with the standard
installation of PVTi under the directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
The tutorial is split into several sections:
•
"Introduction" on page 54
•
"Exporting water properties" on page 54
•
"Generating ECLIPSE Black Oil PVT tables" on page 54
•
"Importing the keywords into ECLIPSE Office" on page 57
•
"Discussion" on page 57
Introduction
Once the fluid description has been fitted to the experimental observations, it may be used in a
reservoir simulation. PVTi facilitates the transition between a fluid description and the PVT
keyword description required by the ECLIPSE family of simulators.
In this tutorial PVT tables are created for the fluid definition developed in the tutorials 2, 3 and
4. The output tables are then used in an ECLIPSE simulation.
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
Open REGRESS_SECTION.PVI created in the last tutorial (alternatively, open
REGRESS_CORRECT.PVI ).
Exporting water properties
The water properties exported from PVTi are generated by correlation. This is effectively
separate from the fluid model.
1
2
PVTi: File | Export Keywords | Water...
a
Enter a reservoir temperature of 220 F and an initial reservoir pressure of 2500 psig.
b
Click on OK
c
Enter the filename PVTW.PVO for the water keyword
Close Output Display panel.
Generating ECLIPSE Black Oil PVT tables
In order to generate ECLIPSE BlackOil simulation PVT tables, PVTi requires either a
Differential Liberation experiment or a Constant Volume Depletion experiment to be simulated
from the fitted equation of state. The PVT tables are generated off either of these experiments.
54
Tutorials
Exporting ECLIPSE Black Oil PVT tables
PVTi Reference Manual
1
Right-click on experiment DL1 in the sample tree and select Export Keywords... from the
drop-down menu
Hint
2
PVTi: File | Export Keywords | Oil reservoir... produces an export panel for all
available Differential Liberation experiments.
Select PVTO and PVDG (Live oil and dry gas) on the radio button menu.
The Separators drop-down menu becomes active. This is because the produced fluid from
the Differential Liberation experiment must be passed through a surface separator to
calculate, for example, surface gas-oil ratios. The default is a separator at Standard
Conditions. If any separator experiments were defined for this sample, they would also
appear here.
3
Click OK
4
In the File Selection box, enter ECLIPSE100 as the name of the export file.
The keywords are generated and the Display Output module shows the generated keywords.
Note
The comments prefixed with --PVTi that appear before each keyword are the concise
version of the current PVTi project. This is the minimum information PVTi requires to
create the tables. This information can be used to rapidly convert an ECLIPSE
BlackOil data-set to an ECLIPSE Compositional data-set.
Caution
Note
Avoid editing the --PVTi prefixed comments. Any changes may invalidate the
file, preventing PVTi from reading it.
The sample SWELLSAM has been added to the sample tree. This sample is the swelled
sample that was obtained by swelling the original sample with vapor that was split off
just below the bubble-point of the fluid. PVTi automatically swells the sample with the
vapor from the bubble-point so that the table can be extended to values above the
original bubble point.
The information in the keywords is also shown in the main plot space, keyword PVTO is shown
in Figure 5.4.
PVTi Reference Manual
Tutorials
Exporting ECLIPSE Black Oil PVT tables
55
Figure 5.4 Plot of Oil FVF, Viscosity and Rs versus pressure for the output black oil property tables
Generating ECLIPSE Black Oil equilibration
keywords
This is similar to the generation of PVT tables. To generate equilibration tables, a composition
versus depth experiment is required.
1
PVTi: Edit | Experiments...
2
Edit Experiments: Add | Composition with depth...
3
Click Next
4
In the General panel enter the reference properties for the sample:
a
Enter 220 F as the Temperature.
b
Enter 3580 psig as the Pressure.
c
Enter 9200 ft. as the Depth
d
Enter 0 F/ft. as the Temperature gradient.
5
In the Observations panel enter the depths 9000 ft. and 9400 ft.
6
Click Next
7
Click OK to allow PVTi to add extra points between the maximum and minimum depths.
8
Click Close
9
Right-click on the new experiment (COMPG1) in the sample tree and select Export
keywords... from the drop-down menu.
10 Select the RSVD/RVVD (black oil) on the Equilibration Keyword radio button.
56
Tutorials
Exporting ECLIPSE Black Oil PVT tables
PVTi Reference Manual
11 Click OK.
12 Enter the filename RSVD.PVO for the exported keyword.
Note
In this case, only RSVD is generated. This is because the reservoir is all initially in the
liquid phase. If there were a gas-oil contact, both RSVD and RVVD would have been
generated. If the reservoir were all in the gas phase, only RVVD would be generated.
13 PVTi: File | Exit.
Keywords have now been generated and can be incorporated into an ECLIPSE data-set using
ECLIPSE Office.
Importing the keywords into ECLIPSE Office
This section is not intended as a tutorial on using ECLIPSE Office. Refer to the "ECLIPSE
Office User Guide" for details on using the product.
1
Start ECLIPSE Office with a new case (call it PVTI_TUTORIAL.OFF ) and import the
standard data set ECLIPSE100.DATA
2
Click ECLIPSE to let ECLIPSE Office know what type of data-set is being imported.
3
Open the Data Manager.
4
Open the PVT Sections.
5
PVT Section: File | Import | Append..., and import the PVT table keyword file
(ECLIPSE100.PVO). Click OK to remove the warning message.
6
PVT Section: File | Import | Append..., and import the water keyword file (PVTW.PVO).
Click OK to remove the warning message
Note
At this stage you may want to view the keywords or plot them. For details on how to
do this, refer the "ECLIPSE Office User Guide".
7
Close the PVT Section, saving the file with the new keywords.
8
Open the Initialisation Section
9
Initialisation Section: File | Import | Append..., and import the equilibration keyword file
(RSVD.PVO). Click OK to remove the warning message.
10 In the Equilibration Data Specification keyword, set the Rs/Pb v Depth Table to 1, so
that the imported RSVD keyword is used.
11 Close the Initialisation Section, saving the file with the new keywords.
12 Run the simulation.
Discussion
In this tutorial an existing fluid definition was imported into PVTi and exported as PVT tables
that were used in an ECLIPSE Black Oil reservoir simulation. The basic requirements are that
PVTi must simulate a Constant Volume Depletion or Differential Liberation experiment and a
Separator experiment to allow the generation of black oil tables from the fluid definition.
PVTi Reference Manual
Tutorials
Exporting ECLIPSE Black Oil PVT tables
57
Converting a black oil run to compositional
This tutorial provides an example conversion from ECLIPSE BlackOil to ECLIPSE
Compositional. This tutorial requires the use of ECLIPSE Office in combination with PVTi.
Note
Many conversion projects require conversion of SCHEDULE section keywords, which
is outside the scope of this tutorial. This tutorial covers conversion of fluid properties
and equilibration. Specifically, the PROPS and SOLUTION sections.
Note
Some familiarity with ECLIPSE Office is assumed for this tutorial.
The data for this project are provided with the standard installation of PVTi under the directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
Note
You should choose a short name for your directory and the name must not contain
spaces. You can use underscore characters. ECLIPSE does not recognize directory
names that are long or that contain spaces.
The tutorial is split into several sections:
•
"Introduction" on page 58.
•
"Exporting the fluid model" on page 59.
•
"Converting equilibration keywords" on page 59.
•
"Creating the ECLIPSE Compositional case" on page 60.
•
"Discussion" on page 60.
Introduction
In this tutorial, the black oil PVT tables (PVTO and PVDG) and the Equilibration table (RSVD)
are converted into a full compositional model and composition versus depth table (ZMFVD).
This allows the ECLIPSE data-set from the previous tutorials to be run as a full compositional
case.
Caution
58
The --PVTi comments written out with the keywords are used by PVTi to
reconstruct the original fluid model. Without these there is not enough information
to convert blackoil projects to compositional models. It is important that the lines
prefixed by --PVTi in the ECLIPSE data-set are not edited or moved around
in the file.
1
Start ECLIPSE Office with the project created in "Exporting ECLIPSE Black Oil PVT
tables" on page 54 or create a new project and load in the data-set
ECLIPSE100_FULL.DATA .
2
Select the case.
Tutorials
Converting a black oil run to compositional
PVTi Reference Manual
3
Click on the PVTi launch button.
4
Click Run.
Note
The launch button has a default selection of launching PVTi with the PVT section of
the current case. PVTi reads this PVT section, creating a PVI file from the --PVTi
comments.
Exporting the fluid model
The imported PVT section contains the samples from the original PVI file plus any experiments
that were needed to generate the keyword. In this case the experiments are a Differential
Liberation experiment and a separator.
1
PVTi: File | Export Keywords | ECLIPSE Compositional Fluid Model...
2
Select the fluid {None}.
This means that PVTi does not write out a ZI keyword for the ECLIPSE Compositional
fluid model. This is the correct selection in this case as the equilibration (RSVD) is used to
create a composition versus depth table ( ZMFVD).
3
Enter the reservoir temperature as 220o F.
Hint
The reservoir temperature is the temperature in the Differential Liberation experiment
definition. You can right-click on the DL1 experiment and select Edit... from the dropdown menu to view the definition of the Differential Liberation experiment.
4
Click OK.
5
Export the fluid model to FLUID.PVO
6
PVTi: File | Exit (There is no need to save the PVI file as it can be created from the
ECLIPSE Office case).
Converting equilibration keywords
1
In ECLIPSE Office, click on the PVTi launch button.
2
Select Initialisation as the section to launch PVTi with.
3
Click Run.
Hint
Again, PVTi searches for the --PVTi comments and uses them to construct a PVI
project file.
4
In PVTi, right-click on the composition versus depth experiment COMPG1.
5
Select Export keywords... from the drop-down menu.
6
In the COMPG1 export panel, select ZMFVD (Compositional) on the radio button.
7
Click OK.
8
Export the keyword to the file ZMFVD.PVO.
PVTi Reference Manual
Tutorials
Converting a black oil run to compositional
59
9
PVTi: File | Exit (there is no need to save the PVI file as it can be created from the
ECLIPSE Office case).
Creating the ECLIPSE Compositional case
1
ECLIPSE Office: Case | Add Case | Clone .
This creates an identical copy of the original case.
2
Name the case COMPOSITIONAL, and click OK.
3
Select the newly created case.
4
ECLIPSE Office: Module | Data Manager...
5
Select the Case Definition.
6
In the Case Definition module, select Compositional on the Simulator radio button.
7
Click OK to the warning about changing between black oil and compositional cases.
8
In the PVT folder set the number of components to 11, and click OK.
9
In the Data Manager, select the PVT section.
10 PVT Section: File | Import | Append... and import the file FLUID.PVO.
11 PVT Section: File | Import | Append... and import the file ZMFVD.PVO.
12 PVT Section: Section | Keywords...
13 Delete the PVTO and PVDG keywords.
14 PVT Keywords: File | Close...
15 PVT Section: File | Close... and save the section with a new name.
16 In the Data Manager select the Initialisation section.
a
Delete the RSVD keyword.
b
In the EQUIL keyword set the Compositional init type to 1 (so that ZMFVD is used
for equilibration).
17 Initialisation Section: File | Close and save the section with a new name.
18 Run the simulation from the ECLIPSE Office Run Manager.
Discussion
In this tutorial, an ECLIPSE BlackOil simulation data-set was converted to ECLIPSE
Compositional using the integration of PVTi and ECLIPSE Office.
The insertion of the --PVTi comments into the keyword export from PVTi is a powerful tool,
not just for converting data-sets, but also for developing projects in either black oil or
compositional models.
60
Tutorials
Converting a black oil run to compositional
PVTi Reference Manual
Workflow Tutorial
Introduction
This tutorial illustrates a typical workflow for an oil or gas condensate. It involves splitting the
C7+ fraction into 2 pseudocomponents, special regression, normal regressing, grouping
components, and matching viscosity data.
We have an oil PVT case, with two fluid samples ZI and W2 (Well 2). There is a C7+
characterization with CO2 present. Well 2 has C7+ has a different MW and Specific Gravity,
but the C7+ has been characterized with the ZI fraction only at this point. They are going to
inject CO2 into this field, so there is a Swelling Test with CO2.
The files for this tutorial are provided in the default PVTi installation in the following directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
This tutorial contains the following sections:
•
"Comparing the Default EOS Calculations to the Observations" on page 61.
•
"Splitting the C7+ Component" on page 62.
•
"Special regression to adjust the tail in the splitting calculation" on page 63.
•
"Normal regression to fine tune 11 component match" on page 64.
•
"Grouping Like Components to Reduce Nc" on page 64.
•
"Regressing to match viscosities" on page 67.
•
"Discussion" on page 68.
Comparing the Default EOS Calculations to the
Observations
1
Start PVTi.
2
Open WORKFLOW.PVI.
3
Run the Simulations; to do this click GO.
4
Review the calculated and observed Bubble Point Pressures for fluid ZI and W2 in the
Output Display, that is the first and last experiments.
5
Close Output Display panel.
6
Plot the results one experiment at a time.
7
PVTi Reference Manual
a
Right-click on CCE1 - Plot.
b
After reviewing the plots clear the plots by clicking the Remove Plots button.
Review all the experiments by observing the plots noting how well PVTi has done in each
case in matching the observations.
Tutorials
Workflow Tutorial
61
Splitting the C7+ Component
Creating a phase plot
Before we split we will create a Phase Plot (P versus T)
1
Select View: Samples| Phase plot | ZI; click OK.
2
Rescale the y-axis as follows:
3
a
Double click on the y-axis.
b
Select range.
c
Click off Limit Range.
d
Enter 0.0 in upper Visible Range area.
e
Enter 3000 in lower Visible Range area.
f
Click OK.
Click the “Superimpose“ button or select Options | Graph | Superimpose.
Splitting the C7+
1
Edit | Fluid Model | Split | Multi Feed....
We will split the C7+ into 2 Pseudo components.
2
Note the Mole Weight of the heaviest pseudo component.
3
Enter the following Specific Gravity and Molecular Weight of Samples Plus Fraction
for W2:
Molecular Weight
199
Specific Gravity
0.8338
4
Click OK.
The C7+ has been split.
5
Select Edit | Samples | Compositions.
Check the mole fractions of the 2 pseudo heavy components. The split creates FRC2 with
small mole fraction (0.0477). We would rather have a splitting that has more of the mole
fraction in the heaviest component so we will perform another split.
6
Close this project and do not save the project.
7
Open WORKFLOW.PVI again.
8
Plot the Phase Diagram.
9
Select the Split panel and repeat step 6.
10 This time change the Mole Weight of Heaviest Pseudo Component to 300.
This gives us a larger mole fraction for FRC2.
11 Click OK.
12 Check the Samples.
The FRC2 mole fractions are 8.1% and 13.9%
62
Tutorials
Workflow Tutorial
PVTi Reference Manual
First iteration
1
In the Select EOS parameters for regression panel enter 1 in all the boxes under the
heading VcritV.
2
Click OK.
3
In the Regression panel click Run.
4
Plot the Liquid and Vapor viscosity and compare the new match with the observations.
Second iteration
1
In the Regression panel press Reject to return the characterization back to the preregression values.
2
In the Select EOS parameters for regression panel enter 1 in the first box, 2 in the
second box, 3 through 11 in the remainder of boxes under the heading VcritV.
3
Click OK.
4
In the Regression panel click Run.
5
Plot the Liquid and Vapor viscosity and compare the new match with the observations.
Note this new match is better than the first match.
6
Press Accept to accept these results.
7
Save this characterization with a new file name.
The phase matching process is now complete. You are ready to export the PVT properties or
characterization for ECLIPSE simulations.
Discussion
This tutorial illustrated a typical workflow for an oil or gas condensate. It involved splitting the
C7+ fraction into 2 pseudocomponents, special regression, normal regressing, grouping
components, and matching viscosity data.
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Multiphase Flash
Introduction
The multiphase flash experiment tends to find more than two phases in systems with
Asphaltene/Waxes and/or with CO2 rich fluids at low temperatures. This tutorial demonstrates
multiphase flashes with both systems. The files for this tutorial are provided in the default PVTi
installation in the following directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
The tutorial is split into the following sections:
•
"Asphaltene and wax system" on page 69.
•
"CO2 Rich Fluids" on page 70.
•
"Summary" on page 72.
Asphaltene and wax system
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
Load MULTIPHASE-START1.PVI into PVTi.
3
View this oil composition by selecting Edit | Fundamentals and view the 10 component
oil.When finished click OK.
4
To add an experiment, click Edit | Experiments | Add | Single Point | Multiphase Flash.
5
a
Click Next> and then enter 50 F as the Temperature,
b
Click Observations, fill in 1000 Psia.
c
Click Next> and then Close.
To run the experiment (again) click GO.
The Output Display shows the results of the flash.You will see two phases, Liquid and
Vapor, and their properties and compositions.
Now we are going to split the C7+ fraction into it Paraffin, Naphthalene, and Aromatic
components, then redo the multiphase flash.
6
Select Edit | Fluid Model |Split | PNA Distribution.
The C7+ fraction is now split.
7
To view the new characterization, select Edit | Fluid Model Components.
You will see that there are three new user-defined components which have replaced the C7+
component.
8
Click on the Complete folder to view the critical properties of these components.
9
Click on OK to close the panel.
We are going to run the MFLASH experiment again and view the phases present.
10 Click on GO .
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69
The Output Display shows the following 4 phases: Liquid, Wax, Asphaltene Liquid, and
Vapor.
11 Note that the compositions of the Wax is 100% PC7+ and the Asphaltene Liquid is 90.23%
AC7+.
12 Close the project, do not save the changes.
CO2 Rich Fluids
Certain fluids with a high CO2 content at low reservoir temperatures partition into two liquid
phases or two liquid phases in equilibrium with a vapor phase. This tutorial demonstrates such
a system.
SPE 71485, (see [Ref. 1]) gives fluid characterizations that exhibit multiphase behavior. This
paper describes reservoir oil with 12 components. It has heavy components of C7-9, C10-13,
C14-19, C20-35, and C36+. It also describes an injection gas called (MI, Miscible Injection)
that is a combination of CO2 and NGL. In the paper they use the Peng-Robinson Equation-ofState to calculate the phase behavior. They combine the reservoir oil and the MI gas in various
mixtures at 86 °F and present a diagram of the phases present, which is shown in Figure 5.5.
Figure 5.5 Phase Diagram for Schrader Bluff Fluids
We will attempt to verify the phases present with a 0.8 fraction of MI with PVTi multiphase
flash.
70
1
Load MULTIPHASE-CO2.PVI into PVTi.
This contains the fluids and characterization from the SPE paper,[Ref. 1].
2
View the compositions of the fluid sample by selecting Edit |Samples - Compositions.
3
Click OK to close the panel.
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PVTi Reference Manual
4
To create a mixture of 80% MI and 20% reservoir oil, select Edit | Sample | Mix.
5
In the Mix panel enter the following:
a
Mixing Type By: Mole Fraction of Sample 2
b
Fluid Sample 1: Z1
c
Fluid Sample 2: MI
d
New Sample Name: .8MI
e
Temperature: 86 F
f
Mole Fraction: 80 percent
6
Click OK.
7
To view the new sample, click Edit | Samples | Compositions.
Note the new sample has 65.209% CO2.
Now we will create multiphase flash experiments at a series of pressures (Temperature = 860
F) starting in the Liquid-Liquid region (1100 Psia) then through the Liquid-Liquid-Vapor region
and ending up in the Liquid-Vapor region (600 Psia).
8
Select Edit | Experiments | Add | Single Point | Multiphase Flash.
9
Enter the following:
a
Fluid Sample: .8 MI
b
Temperature: 86 F
10 Select Observations and enter 1100 (psia) as the Pressure = 1100 (psia).
11 Click Next> and Close.
We now have MFLASH1 defined.
12 To create additional MFLASH experiments at a series of lower pressure, right click on
MFLASH1 and select Clone.
13 Repeat for MFLASH2 through to MFLASH5.
We now have 5 MFLASH experiments defined.
14 To change the flash pressures right click on the MFLASH experiment and select Edit |
Observations | Pressure.
15 Enter the following pressure values:
a
MFLASH2: 1050 (psia)
b
MFLASH3: 1000 (psia)
c
MFLASH4: 900 (psia)
d
MFLASH5: 600 (psia)
16 To switch between MFLASH experiments press Next> and then Close.
17 To run all experiments and view results, click GO.
18 Observe the results in the Output Display.
Note as the pressure decreases the flashes proceeds from the L-L region to the L-L-V region
to the L-V regions, just as Figure 5.5 illustrates.
Note
PVTi Reference Manual
The MFLASH5 experiment can sometimes label both the phases as liquid. However,
one of them is clearly a vapor as the density value is 5.64323 lb./ft.3.
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Multiphase Flash
71
Note
If a standard two-phase flash is performed at the same temperature and pressure as with
the multiphase flash, then one obtains liquid and vapor phases with the same density
values as produced with the MFLASH5 experiment.
Summary
This tutorial demonstrated the multiphase flash experiment. It tends to find more than two
phases in systems with Asphaltene/Waxes and/or with CO2 rich fluids at low temperatures.
This tutorial demonstrates multiphase flashes with both systems.
References
Guler B. et al,
"Three- and Four-Phase Flow Compositional Simulations of CO2/NGL EOR"
[Ref. 1]
SPE 71485,
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Exporting an ECLIPSE Thermal model
Introduction
This tutorial demonstrates using the new ECLIPSE Thermal export facility where a file can be
exported containing a fluid model suitable for use in ECLIPSE Thermal. For technical
information on the ELCLIPSE Thermal export facility see "ECLIPSE Thermal Export Module"
on page 401 and for more general workflow guidelines see "Compositional Data for ECLIPSE
Thermal" on page 367. The files for this tutorial are provided in the default PVTi installation in
the following directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
The tutorial is split into the following sections:
•
"Verifying the Validity of the Fluid Model" on page 73.
•
"Fitting the Component K-values" on page 74.
•
"Viewing the K-value Fits" on page 75.
•
"Exporting the Model" on page 76.]
Verifying the Validity of the Fluid Model
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
Open THERMAL.PVI.
3
Open the Fundamentals panel by selecting Edit | Fundamentals....
From the tree view on the left side of PVTi you can see that there is a single sample in this
project called ZI. The Fundamentals panel shows the composition of this 3-component
fluid as being C1, C5 and C20+.
4
On the tree view there are two experiments defined, a Differential Liberation (DL1) and a
bubble point experiment (BUBBLE1). Right-click on the DL1 experiment and selectPlot.
Three observations should have been plotted oil density, oil relative volume and oil
viscosity. You can see that the Equation of State (EoS) fluid model shows good agreement
with all 3 observations.
5
Right-click on the bubble point experiment and select Report.
You can see that the EoS model also gives good agreement with the observed bubble point
pressure of 1784.1749psia.
Since we have a good match for our EoS based fluid model we can now export the model
for use in an ECLIPSE simulation. We have relatively few components (<4) so this fluid
would be suitable for use in an ECLIPSE Thermal simulation.
Note
PVTi Reference Manual
Simulations using ECLIPSE Thermal tend to use fluids consisting of two or three
components.
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Exporting an ECLIPSE Thermal model
73
Fitting the Component K-values
1
Right-click on the sample ZI and select the Export ECLIPSE Thermal model...
2
On the panel that opens, enter the following:
a
1500 psia as the Maximum Pressure,
b
400 F for the Maximum Temperature,
c
1000 psia for the Minimum Pressure,
d
and 200 F in the Minimum Temperature box.
Note
3
The default values here are P max=1000psia, Pmin=50psia, Tmax=400F and Tmin=50F
and are considered reasonable max/min parameters within a reservoir. However, every
reservoir is different and any knowledge of these parameters for your particular
reservoir should be entered.
Enter 40 in the Enter Number of Flashes to be Performed box.
To model component K-values we can either export the KVWI keyword, which models them
using Wilson’s formula, or the KVCR keyword, which uses Crookston’s formula. Crookston’s
formula is in general much more accurate and we will use this. See "K-Values" on page 401 for
a more detailed description regarding the modeling of K-values.
4
Tick the box Export Crookston Coefficient? to tell PVTi that you wish to export the KVCR
keyword.
5
Since we are exporting the KVCR keyword we need to determine the values of the
coefficients of Crookston’s equation to export. Click Fit Crookston Coefficients on the
panel to open the Fit Crookston Coefficients panel.
This panel shows Crookston’s equation where p is the pressure, T is temperature and the
coefficients A-E are what we wish to determine values for.
Note
The Fit Crookston Coefficients panel enables you to calculate the optimum values of
the coefficients A-E in Crookston’s formula, so that the best fit is found to PVTi’s EoS
predicted K-values for each component over the temperature and pressure range
defined by the user.
6
A and D should already be active. Click on B to make coefficient B active also.
7
Select the Plot option in the Plot P, T Values Used in Fitting Crookston Coefficient?
box.
In order to find values for the chosen coefficients PVTi throws in 40 points at random
coordinates in the region you just defined in pressure-temperature space. The Plot option plots
these points on the screen for you after the fit has been performed. Ideally, we would like to them
superimposed on a phase plot.
8
Select PVTi: View | Samples | Phase Plot... and press OK to perform the phase plot.
9
Select PVTi: Options | Graph | Superimpose.
Hint
You can also access the Superimpose option using the toolbar.
10 Now click Apply on the Fit Crookston Coefficients panel to start the run.
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Once the run has finished a results panel appears. In the Coefficients folder the best fit
values of A, B and D are reported for each component.
11 Click on the Statistics panel.
The mean error and standard deviation (in %) are reported for each fit. The C1 and C5
components have been fitted very well (rms<1.5%) and the C20+ fraction has been fitted
reasonably well with an rms of somewhere between 7-9% (depending on the random
number generator on your machine).
Can we do better though?
Caution
Make sure you turn off the Superimpose option before moving to the next
section.
Viewing the K-value Fits
In the last section "Fitting the Component K-values" on page 74 we saw how to use the module
to calculate the optimum values of a chosen set of coefficients in Crookston’s equation in terms
of fitting to PVTi’s Equation of State based K-values. We saw, for the fluid ZI in the
THERMAL.PVI file, that the C20+ fraction had a reasonable fit when using just A, B and D. In
this section we will see how to interactively view the fits in order to better understand why
PVTi’s EoS K-values for this C20+ fraction has not been represented as well as the other
components.
1
Click the View Fit button on the Fit Crookston Coefficients panel.
The Plot K-values vs Temperature or Pressure panel opens.
Hint
Plots can either be performed of K-values versus pressure (at constant temperature) or
K-values versus temperature (at constant pressure).
First we will look at the K-value versus temperature fits, which are dictated by the D and E
coefficients (just D in our case).
2
Enter 1250psia in the Enter Constant Pressure box and 400F and 200F as the
Maximum and Minimum Temperatures respectively. Now click Apply.
The PVTi EoS-based K-values are shown by the points and the K-values calculated using
Crookston’s equation are shown by the curves.
3
Experiment by changing the value of the constant pressure in the range 1000<P<1500 (our
chosen pressure range) to see how well Crookston’s formula models the temperature
dependence of the K-values at a given pressure.
In general, for the C20+ component, the D coefficient, models the observations pretty well
over the whole pressure-temperature range, although using the E coefficient as well may
well help slightly
4
Click the Plot at Constant Temperature box and enter 300F.
5
Now enter the appropriate pressure range, which is 1500 psia and 1000 psia for the
maximum and minimum values. Click Apply.
6
Again, experiment by changing the value of the constant temperature in the range
200<T<400 to see how well Crookston’s formula models the pressure dependence of Kvalues.
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75
In particular it can be seen in the range 300<T<400 (for the C20+ component) that
Crookston’s formula struggles to model the pressure dependence at pressures at
P<1100psia when using just the A and B coefficients. Using the C coefficient may well
improve things significantly.
You can see in particular, the K-value versus pressure curve for the C20+ component
struggles to fit the observations.The problem is that the term A+B/P starts to run into
problems for pressure values <1100psia (due to the strongly negative value of B) and
therefore we require the C coefficient to get a good fit.
7
Close the Crookston Report panel and the Plot K-values vs Temperature or Pressure?
panel.
8
Switch on the C and E coefficients by ticking the appropriate boxes on theFit Crookston
Coefficients panel. Now click Apply.
This run will take slightly longer, as the introduction of the C and E terms vastly increases
the amount of parameter space that PVTi must search.
9
Once the run has finished repeat steps 1-3.
This time, due to the introduction of the C coefficient in the fit, we have done a better job
in fitting the pressure dependence of Crookston’s equation. The introduction of the E
coefficient has also slightly improved the modeling of the C20+ K-value versus
temperature.
10 Click on the Statistics folder.
Overall, the introduction of the C and E coefficients has decreased the rms fit for the C20+
component from ~8% to ~5%.
Exporting the Model
Now we are satisfied with our K-value fits we can export our ECLIPSE Thermal PVT model.
Note
If we had decided to export the KVWI keyword (that is use Wilson’s formula to model
K-values) then we would not have needed to fit the coefficients of Crookston’s
equation and could have exported straight away from the Export for ECLIPSE
Thermal panel. Although this may be quicker, Crookston’s formula models K-values
much better and spending this extra time is worthwhile.
1
Click the OK button on the Export for ECLIPSE Thermal panel.
2
Choose a name for the file to be exported.
By default PVTi names it rootname.PVOT, so in this case THERMAL.PVOT if you do
not choose otherwise.
3
Click Save.
The ECLIPSE Thermal fluid model is written to the specified file. This file can now be used
to model PVT behavior as part of an ECLIPSE Thermal simulation.
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PVTi Reference Manual
Data analysis and quality control
This tutorial provides a typical workflow for PVTi in its role as a data quality assessment tool.
Experimental results from analysis of a hydrocarbon gas is used to analyze the data quality and
to modify spurious data. The data for this project are provided with the standard installation of
PVTi under the directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
The tutorial is split into several sections:
•
"Introduction" on page 77
•
"Material balance checking" on page 78
•
"The Hoffman-Crump-Hocott test for separator data" on page 82
•
"Recovery calculations" on page 83.
Introduction
In addition to allowing an equation of state to be fitted to laboratory results and facilitating the
generation of ECLIPSE BlackOil/ Compositional PVT data, PVTi also provides material
balance checks to assess data quality. For information on the calculations involved in material
balance checking see "Compositional material balance" on page 307.
Note
Problems with the observations in a PVT report equate to problems with the fitted fluid
model. It is therefore recommended that material balance checks are carried out on all
PVT data.
In this tutorial an existing project file (GAS.PVI) is read into PVTi and the data are checked
and modified for material balance errors.
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
PVTi: File | Open...
3
Open GAS.PVI
Hint
4
The Data Tree should show that there are two experiments, CVD1, defined with 10
different types of observations, SEPS1 with observations of fluid mole fractions
(liquid and vapor) and CCE1 with observation of Vapor Z-Factor.
Click and drag the ZI node from the Data Tree and drop it into the Main Plot Window.
The phase envelope should look like Figure 5.6.
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77
Figure 5.6 The phase envelope plot.
Note
This fluid system has no well-defined critical point.
Material balance checking
1
Right-click on CVD1 in the sample tree and select Material Balance...
This opens the Material Balance panel for this experiment.
2
Click Report to create a material balance report.
The experiment is performed and the Output Display window opens showing messages
that indicate the quality of the data. (Figure 5.7)
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Figure 5.7 The main display shows messages indicating the quality of the data
Warning
Warning
Warning
Warning
- Sg of final stage liquid plus fraction is not defined
- Mw of final stage liquid plus fraction is not defined
- Viscosities of gas of at least one stage of CVD is not defined
- Mw of vapor plus fraction of at least one stage is not defined
- setting constant Mw(CN+) = of Mw(CN+) at Psat
Warning - Sg of vapor plus fraction of at least one stage is not defined
Warning - Composition of final stage liquid does not sum to 100%
Calculated liquid mole% of N2
at P= 6300.00000 is negative
Calculated liquid mole% of CO2 at P= 6300.00000 is negative
Calculated liquid mole% of IC4 at P= 6300.00000 is negative
Calculated liquid mole% of NC4 at P= 6300.00000 is negative
Calculated liquid mole% of IC5 at P= 6300.00000 is negative
Calculated liquid mole% of NC5 at P= 6300.00000 is negative
Calculated liquid mole% of C6
at P= 6300.00000 is negative
Calculated liquid mole% of N2
at P= 5700.00000 is negative
Calculated liquid mole% of CO2 at P= 5700.00000 is negative
Calculated liquid mole% of N2
at P= 5100.00000 is negative
Calculated liquid mole% of CO2 at P= 5100.00000 is negative
Calculated liquid mole% of N2
at P= 4500.00000 is negative
Calculated liquid mole% of N2
at P= 3800.00000 is negative
Calculated liquid mole% of N2
at P= 3100.00000 is negative
Calculated liquid mole% of N2
at P= 2400.00000 is negative
Calculated liquid mole% of N2
at P= 1700.00000 is negative
Calculated liquid mole% of CO2 at P= 1700.00000 is negative
Calculated liquid mole% of N2
at P= 1000.00000 is negative
Calculated liquid mole% of CO2 at P= 1000.00000 is negative
Calculated liquid mole% of N2
at P=
300.00000 is negative
Calculated liquid mole% of CO2 at P=
300.00000 is negative
The messages show that some mole fractions were calculated as negative, so there are
clearly problems with the data. PVTi supplies various options for plotting the data to
ascertain the source of the errors. The first type of data check to perform is to view the
pressure variation of the gas compositions.
3
Output Display: File | Close
4
Click Plot in the Material Balance panel.
a
Select Vapor Compositions v Pressure in the Select Plot Type panel and click on
Plot.
b
Click Close
5
PVTi: View | Rubberband Zoom In
6
Click and drag the mouse to define the zoom area to approximately cover the region 2800
to 6500 psia and 0.1 to 2 vapor composition. After zooming in, the plot window should look
similar to Figure 5.8.
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79
Figure 5.8 The main plot window after zooming in
Many of the components have non-monotonically varying gas compositions. In general, there
are several fluids or analyses available, and bad data can be discarded. However, if no other data
is available PVTi offers tools to make modifications to the bad data.
Modifying CVD data
1
Click Modify in the Material Balance panel.
2
Select fraction modifiers.
3
Enter the following values in for 6996 psia:
Component
N2
CO2
...
IC4
NC4
IC5
NC5
C6
Percentage
10
10
...
2
10
5
5
20
Note
80
The other components are modified in proportion to their existing mole fractions.
Placing a letter in the thin column to the left of each column of modifiers allows the
proportion of that component to be fixed and thus not modified in proportion to its
existing mole fraction.
4
Click on OK in the Set correction factors for CVD compositions panel.
5
Click Report in the Material Balance panel to create a new material balance report.
6
Click on Yes to modify the compositions on CVD vapor and Liquid Composition
Modif... panel.
7
Click on No on the CVD vapor and Liquid Composition to ... panel so that the
compositions are saved, but retain their original values until after the modified results have
been examined.
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Data analysis and quality control
PVTi Reference Manual
Now none of the liquid mole percentages are negative. So this change to the data can be
accepted.
8
Click Report in the Material Balance Panel
9
Click on Yes to modify the compositions.
10 This time, click on Yes so that the compositions are modified.
Plotting K values versus Pressure
1
Click Plot in the Material Balance panel.
2
Select K-values:(1) log (k) v Pressure plot in the Select Plot Type panel and click on
Plot.
The plot window should now look like Figure 5.9.
Figure 5.9 The plot of k values versus pressure.
The K-values should plot monotonically in that N2 should be the largest, followed by C1, etc.
This is clearly not the case, so although there are now no calculated negative compositions, the
modified fluid definition is not fully consistent.
The Hoffman-Crump plot
1
Select the K-values:(2) Hoffman-Crump Plot in the Select Plot Type panel and click on
Plot.
2
Click Close in the plot panel.
3
Click Close in the Material Balance Panel.
The plot window should look like Figure 5.10.
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81
Figure 5.10 The Hoffman-Crump plot
In this plot, one line is generated for each pressure stage. The Hoffman F coefficients
correspond to C1, C2 etc. and the lowest to C11, C12+. In general, these lines should be
monotonic with pressure, with the highest pressure at the top. This plot shows most of the error
to be in the first stage.
The Hoffman-Crump-Hocott test for separator data
Applying the Hoffman-Crump-Hocott test to separator gas and oil samples indicates whether or
not the streams are genuine equilibrium fluids.
1
Right-click on SEPS1 in the project tree-view and select Recombination... on the pop-up
menu.
2
Click Report to create a recombination report.
3
Output Display: File | Close
4
Click Plot.
The two lines on the Hoffman-Crump-Hocott plot (Figure 5.11) show the actual data and
the Standing estimates of K-values. They are used as a consistency check and, in this case,
give further evidence that the initial feed stream composition is in error.
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Figure 5.11 Hoffman-Crump-Hocott plot.
Recovery calculations
PVTi can allow recovery calculations to be performed if a valid Constant Composition
Expansion, Constant Volume Depletion and Separator test exist.
1
Right-click on CCE1 in the project tree-view and select Recovery... on the pop-up menu.
2
Click on Report to perform the recovery calculation.
Hint
This assumes that there is no direct production of reservoir liquid. If you want to
include direct production of reservoir liquid, you need a relative permeability table,
which you can enter be clicking on Rel. Perm.
Note
PVTi runs the material balance check on the Constant Volume Depletion experiment
selected, and performs recombination on the Separator selected, before performing the
recovery calculation.
Discussion
This tutorial has illustrated how fluids may be examined for consistency and, if necessary,
modified, within a PVTi project.
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Data analysis and quality control
83
Removing contamination from samples
Introduction
Oil-based muds are in widespread use and often contaminate PVT samples taken at the wellsite.
This tutorial involves the cleaning of a sample that is contaminated by an oil-based mud.
The PVI file CLEAN.PVI is used for this tutorial and is provided in the default PVTi
installation in the following directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
The tutorial is split into several sections:
•
"Introduction" on page 84
•
"Removing oil-based mud contamination by skimming" on page 84
•
"Removing oil-based mud contamination by subtraction" on page 85
•
"Discussion" on page 86
Removing oil-based mud contamination by
skimming
1
Start PVTi (if you are unsure about this see "Starting PVTi" on page 31).
2
Open CLEAN.PVI.
3
Right-click on the sample ZI and select Fingerprint plot from the drop-down menu.
In naturally occurring hydrocarbons there is expected to be semi-log straight-line behaviour
for components C8+ (around a mole weight of 100). From the fingerprint plot, there is
clearly not straight-line behavior for this fluid.
The contaminating mud, like many oil-based muds, has a composition containing
components C10-C23. In the skimming method, it is assumed that the composition is not
known.
4
Right-click on the sample ZI and select Clean... from the drop-down menu.
a
Enter CLEAN as the sample name for the cleaned sample.
b
Enter CONTAM as the sample name for the contaminant.
c
Click OK.
The sample has now been cleaned.
5
PVTi: Options | Graph | Superimpose - and ensure that the Superimpose option is on.
6
Right-click on the sample CLEAN and select Fingerprint plot from the drop-down menu.
7
Right-click on the sample CONTAM and select Fingerprint plot from the drop-down menu.
The plot should now look like Figure 5.12.
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Figure 5.12 The original sample, the cleaned sample and the estimated contaminant.
Removing oil-based mud contamination by
subtraction
When the composition of the contaminant is known, the subtraction method can give better
results than the simple skimming method.
1
Right-click on the sample MUD and select Fingerprint plot from the drop-down menu.
The true composition of the contaminant contains components lighter than C8 and also up
to the plus-fraction (C25+). The skimming method could not remove this contaminant
completely, but the subtraction method can.
2
3
PVTi Reference Manual
Right-click on the sample ZI and select Clean....
a
Enter CLEAN2 as the sample name for the cleaned sample.
b
Select Subtraction as the method.
c
Select MUD in the Contaminant drop-down.
d
Click OK.
Right-click on the sample CLEAN2 and select Fingerprint plot from the drop-down menu.
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Removing contamination from samples
85
Discussion
This tutorial showed how a fluid can be cleaned of oil-based contaminants such as drilling
muds. For information on how the skimming and subtraction methods work see "Removing
contamination from samples" on page 84.
In general different PVT samples contain different levels of contaminant. It is usually best to fit
the PVT reports from a number of (contaminated) samples. Once a consistent fluid model has
been developed, the samples can be cleaned using either of the methods outlined in this tutorial.
The cleaned samples can then be used in reservoir simulations.
86
Tutorials
Removing contamination from samples
PVTi Reference Manual
Converting old projects to the current version
This tutorial demonstrates conversion of an old project to the current version of PVTi. This is
especially important for projects (PVI files) created with versions before 99B, as the default
Field units for Gas Formation Volume Factor were changed for that release. The files for this
tutorial are provided in the default PVTi installation in the following directory:
$ECL/2007.1/pvti/tutorials
and should be copied to the local directory before starting the tutorial.
The tutorial is split into several sections:
•
"Introduction" on page 87
•
"Preparing the PVI file for conversion" on page 87
•
"Converting the file" on page 88
•
"Discussion" on page 88.
Introduction
The VERSION keyword, introduced in 2000A, allows a systematic method for updating old
PVI files to be compatible with the latest version of PVTi. This tutorial describes how the
keyword can be used to convert an old PVI file into the current version.
Caution
Files in FIELD units containing Differential Liberation (DL) experiments that
have Gas formation volume factor ( GFVF) observations must be updated to the
current version.
Preparing the PVI file for conversion
1
Start PVTi with a new project.
2
Click Cancel in the Fundamentals panel.
3
PVTi: Utilities | Text Editor
4
Select OLD.PVI as the file to be viewed
5
In OLD.PVI enter the VERSION keyword in the RUNSPEC section with a value of 98B.
Hint
If you are unsure of the form of the VERSION keyword see "VERSION" on page 280.
6
File | Save As...
7
Save the file with the name CONVERT.PVI
8
File | Close
Note
PVTi Reference Manual
You could now use the file CONVERT.PVI in a normal session and PVTi interprets it
according to the version specified by the VERSION keyword.
Tutorials
Converting old projects to the current version
87
In this tutorial we go one step further and convert the PVI file to the current version.
Converting the file
1
PVTi: File | Open
2
Select CONVERT.PVI as the file to open.
3
PVTi: File | Save As...
4
Save the file with the name NEW.PVI
Hint
You can compare the file NEW.PVI to OLD.PVI to see the differences (the DL
observation GFVF is converted from rb/stb to rb/Mscf and the heat capacity keywords
are added in the SYSTEM section).
Discussion
In this tutorial an old PVI file was converted to the latest version. This is important for files
using FIELD units, containing Differential Liberation (DL) experiments that have Gas
formation volume factor (GFVF) measurements as the units, for this type of observation was
changed in 99B from rb/stb to rb/Mscf to make PVTi’s units systems consistent with those of
the ECLIPSE simulators.
88
Tutorials
Converting old projects to the current version
PVTi Reference Manual
Reference section
Chapter 6
General information
•
"Main PVTi window" on page 90
•
"File" on page 92.
•
"View" on page 95
•
"The fluid model" on page 98
•
"COMB - Compositional Material Balance" on page 112
•
"Simulation using PVTi" on page 117
•
"Regression in PVTi" on page 126
•
"Exporting keywords" on page 133.
•
"Utilities" on page 144.
•
"Batch system and keywords" on page 152.
•
"Error handling" on page 165.
PVTi Reference Manual
Reference section
General information
89
Main PVTi window
General information
PVT analysis involves fitting an Equation of State to experimental data and then using the
Equation of State to produce PVT tables for use in reservoir simulations. PVTi contains
facilities to allow you to import experimental data, fit the data to an Equation of State, and
finally produce the PVT tables for reservoir simulation studies.
The menu bar of the main PVTi window has the following options:
90
•
"File" on page 92.
•
"Edit" on page 94
•
"View" on page 95
•
"Run" on page 96
•
"Utilities" on page 97
•
"Graph" on page 97
•
"Window" on page 150.
•
"Help" on page 150.
Reference section
Main PVTi window
PVTi Reference Manual
The PVTi main module
The main module is shown in Figure 6.1.
Figure 6.1 The main PVTi window
Data Tree
Log Window
Equation of State
Main Plot Window and Sub-plots
The main window contains all the tools necessary for Equation of State model fitting.
Basic features
The Data Tree provides a view of the current project’s contents. Each fluid sample is identified
with its experiments as sub-nodes in the tree. Likewise, each experiment has its observations as
sub-nodes. The Log Window is updated with pertinent information relating to actions taken in
PVTi. The Equation of State, upon which the current fluid model is based, is indicated in the
status bar. The Main Plot Window and the Sub-plots provide an area for viewing project
information graphically.
PVTi Reference Manual
Reference section
The PVTi main module
91
File
The File menu allows you to open, close and save PVTi project files (PVI files) and import
sections from PVI files, and provides access to keyword export modules. Graph printing and
plotting facilities are also available from this menu.
•
To open this menu, select File from the main PVTi window.
The File menu consists of the following options:
•
New...
This creates a new PVTi project.
•
Open...
Opens a PVTi project (PVI) file. The complete file is read in and the most recent fluid
model, experiment descriptions, observations, etc., are restored. For more information on
the files PVTi creates see "Files created by PVTi" on page 93.
•
Close...
Closes the current project. If the project is not empty you are asked if you want to save
before closing.
•
Save...
Saves the current PVI file, overwriting the previously saved project.
•
Save As...
Saves the current project to a new PVI file.
•
Save (concise)...
Saves a concise version of the current project containing the latest version of the fluid
model plus any experiments and observations used in simulation and regression. No other
information is saved, therefore information regarding regression variables or split/group
sections will not be recorded by the Save (concise) option.
•
Export Keywords
This provides access to the Keyword Export modules. Currently PVTi supports export for
the ECLIPSE simulators and VFPi. See "Exporting keywords" on page 133.
•
Import
This option allows a section from a previous PVI project or ECLIPSE data-set to be
imported or a “concise” PVI project to be merged with the current project. The sections that
can be imported here are SYSTEM,GROUP, SPLIT,SIMULATE and REGRESS. See
"Reading the SYSTEM section from a PVI or DATA File" on page 98.
•
View PVI Section
This opens a particular section from a PVI file and displays the keywords in a text editor.
The sections that can be viewed this way are SYSTEM, GROUP, SPLIT, SIMULATE, and
REGRESS. See "Displaying the SYSTEM section from a PVI file" on page 98.
•
Exit
This exits PVTi. If there is an active project, you are asked whether you would like to save
the project before exiting.
92
Reference section
The PVTi main module
PVTi Reference Manual
Files created by PVTi
All files in PVTi use the project name as their base name. PVTi creates the following files:
•
PVI file, for example ALL.PVI
Input data file, although can be written by PVTi to save system specification or session.
•
PVP file, for example ALL.PVP
Main printed output file. In interactive mode a prompt to write results to this file follows
most operations.
•
PVO file, for example ALL.PVO
Output file. Used for the output of ECLIPSE Black Oil, GI option (pseudo-compositional)
or ECLIPSE 300 (equation of state) properties.
•
VEC file, for example ALL.VEC
Vectors file. Contains vectors of plots performed in a PVTi section in a form suitable for
inclusion into the GRAF program.
•
DBG file, for example ALL.DBG
Debug file. This is only present if debug has been written.
•
MES file, for example ALL.MES
Message file. A temporary file used throughout the program run to display results. This file
is deleted when you quit the program.
•
LOG files, for example ALL.LOG
Program Log File. This file exists in the startup directory of the program and contains a
summary of keywords read in, tasks performed, etc.
•
NEW files, for example ALL.NEW
New data file. This is a temporary file that holds the details of the new .PVI file. It is left
in the working directory if the program does not shut down cleanly.
Hint
•
The .NEW file contains all the changes made during the last session. If you change the
file extension to .PVI you can use it to recover the session.
REG files, for example ALL.REG
Regress Module file. This temporary file holds details of the quantities plotted in the
Regress module. It is left in the working directory if the program does not shut down
cleanly.
Only one project at a time can be in use with a single run of PVTi. To open another project, close
the current project, either by selecting the File | Open option (the program prompts you save
the session to a new .PVI file) or by using File | Close.
Note
PVTi Reference Manual
Although only one project may be in use by the program, different sections of different
.PVI files may be read in.
Reference section
The PVTi main module
93
Edit
The Edit menu allows entry and editing of the fluid model, samples, experiments, observations
and regression variables.
1
To open this menu, select Edit from the main PVTi window.
The Edit menu consists of the following options:
•
Fundamentals...
This opens the Fundamentals panel, See "Fluid Properties Estimation" on page 34.
•
Fluid Model
This opens the sub-menu of fluid model editing options.
•
Equation of State... This opens the Equation of State selection panel. See "Equation
of State" on page 100.
•
Components... This opens the component properties panel. See "Components" on
page 101.
•
Binary Interaction Coefficients... This opens the binaries panel. See "Binary
Interaction Coefficients" on page 104.
•
Volume Shifts... See "Volume shifts" on page 104.
•
Thermal Properties... See "Thermal properties" on page 104.
•
LBC Viscosity Coefficients... See "LBC Viscosity Coefficients" on page 104
•
Split This opens the sub-menu of options for splitting fluid components. See "Splitting
components" on page 105.
•
•
•
Constant Mole Fraction...
•
Whitson...
•
Multi-feed...
•
PNA Distribution
Group...
Samples.
This opens the sub-menu of sample entry and editing options.
•
•
Names... See "Sample names" on page 107.
•
Compositions... See "Sample compositions" on page 107.
•
Salinities... See "Sample salinities" on page 107.
•
Mix... See "Mixing samples" on page 108.
Properties Estimation (FPE)...
See "Fluid Properties Estimation" on page 34.
•
Experiments...
See "Defining Experiments" on page 117.
•
Observations...
See "Defining Observations" on page 122.
94
Reference section
The PVTi main module
PVTi Reference Manual
View
The View menu provides facilities for plotting and reporting.
1
To open this menu select View from the main PVTi window.
The View menu has the following options:
Samples: This option opens a sub-menu containing sample plot types.
•
•
Phase plot. See "Sample phase plot" on page 109.
•
Fingerprint plot. See "Sample fingerprint plot" on page 108.
•
Ternary plot. See "Sample ternary plot" on page 110.
•
Observations... This allows you to plot an observations against calculated values, or any
calculated values where corresponding observations do not exist.
•
Library. This option allows you to view the internal PVTi library. See"Library" on page 95.
Library
The properties of library components are preset by the program.
To display the current list of library components select View | Library...
Table 6.1
PVTi Reference Manual
List of library components
Mnemonic
Name
Mnemonic
Name
H2 O
Water
N2
Nitrogen
H2
Hydrogen
H2 S
Hydrogen Sulfide
CO 2
Carbon Dioxide
CO
Carbon Monoxide
C1
Methane
C2
Ethane
C3
Propane
C4
Butane
iC 4
Iso-Butane
nC 4
Normal Butane
C5
Pentane
iC 5
Iso-Pentane
nC 5
Normal Pentane
C6
Hexanes
C6 H6
Benzene
C7 H8
Toluene
C7
Heptanes
C8
Octanes
C9
Nonanes
C 10
Decanes
C11
Undecanes
C 12
Dodecanes
C13
Tridecanes
C 14
Tetradecanes
C15
Pentadecanes
C 16
Hexadecanes
C17
Heptadecanes
C 18
Octadecanes
C19
Nonadecanes
C 20
Eicosanes
Reference section
The PVTi main module
95
Table 6.1
List of library components (Continued)
Mnemonic
Name
Mnemonic
Name
C 21
C21’s
C22
C22’s
C 23
C23’s
C24
C24’s
C 25
C25’s
C26
C26’s
C 27
C27’s
C28
C28’s
C 29
C29’s
C30
C30’s
C 31
C31’s
C32
C32’s
C 33
C33’s
C34
C34’s
C 35
C35’s
C36
C36’s
C 37
C37’s
C38
C38’s
C 39
C39’s
C40
C40’s
C 41
C41’s
C42
C42’s
C 43
C43’s
C44
C44’s
C 45
C45’s
Note
For components C6 to C 45 , the properties stored in the internal library correspond to
the “grouped” properties of Single Carbon Number Groups (SCN), [Ref. 5].
Obvious candidates for the pseudoisation of components for use in large regressions or
compositional simulation are iso-butane and normal butane, and iso-pentane and normal
pentane, into single butane and pentane components. A study of many PVT reports [Ref. 19]
has shown that the typical ratios of iC 4 : nC 4 , iC 5 : nC 5 are 0.67:0.33 and 0.60:0.40 respectively.
The library also contains two other components, with the mnemonics C4 and C 5 , whose
properties are mole-weighted averages of the respective iso and normal component properties.
Run
The Run menu provides simulation and regression facilities.
The following options are available:
•
Check Fluid System.
This provides a consistency check of the current fluid, the results of which are posted to the
log window. If there are a lot of fluid errors, the results are also displayed in a text window.
•
Save As Samples .
If this option is turned on, any samples created by an experiment can be saved as additional
project samples.
96
Reference section
The PVTi main module
PVTi Reference Manual
•
Simulate
This simulates all active experiments and then display the simulation results in a text editor.
PVTi has intelligent simulation, which means that the results of the last simulation run are
stored, and if no change has been made to the experimental data the simulation run is not
repeated, the results from the previous run being used. This keeps the time spent running
simulations to a minimum.
•
Regression...
This opens the Regression panel. See "Regression in PVTi" on page 126.
Utilities
The Utilities menu option provides access to miscellaneous information relating to the project
and program set-up.
•
Units...
See "Units..." on page 144.
•
Standard Conditions...
See "Standard conditions..." on page 145.
•
Program
This opens the sub-menu of program configuration options.
•
•
Options... This opens the Options panel which mimics the OPTIONS keyword in the
PVI file. See "Program options" on page 145.
•
Debug... See "Debug..." on page 150.
Text Editor
This opens the text editor used for displaying simulation results, etc. It can be used to view
any ASCII file.
Graph
The Graph menu provides options related to the plotting of graphs.
•
Add New Graph...
Adds a new graph to the existing plot windows.
•
Superimpose
When the superimpose option is switched on, indicated by a tick next to the menu option,
subsequent graphs are superimposed on the current main graph.
•
Tabulate...
This option creates a table showing the values plotted in the current main graph.
•
Remove All
This option deletes all graphs from the window.
PVTi Reference Manual
Reference section
The PVTi main module
97
The fluid model
Displaying the SYSTEM section from a PVI file
Displays a RUNSPEC/SYSTEM section present in the current PVI file.
1
To display PVI data, select PVTi: File | View PVI Section | SYSTEM.
Reading the SYSTEM section from a PVI or DATA File
Reads data from a PVI or DATA file. You can use this option to load the equation of state,
viscosity options and hydrocarbon system description from a PVTi PVI file or an ECLIPSE
Compositional (E300) DATA file.
Hint
You can load the first two sections of a PVI file as a system specification, rather than
using menu options. Additionally, you can choose to echo the contents of the whole
PVI file to the current print file, PVP.
Reading the PVT section from an E300 DATA file
1
PVTi: File | Import | ECLIPSE Compositional (*.DATA) and select the appropriate
DATA file.
PVTi searches for the required file and, if found, reads it looking for the number of EoS and
Equilibration regions in the ECLIPSE model. The number of reservoir EoS regions is
defined by the ninth entry of the TABDIMS keyword and the number of Equilibration
regions is defined by the first entry of the EQLDIMS keyword. If the ECLIPSE model has
just one of each region type then the program simply reads in the data. However if multiple
EoS or Equilibration regions are found then the program displays a prompt specifying the
numbers of each region found. You are asked to specify which EoS and/or Equilibration
region they wish to read in.
2
Select the number of the EoS and /or Equilibration region you wish to load.
Note
EoS regions each have an EoS model defined within them that is an EoS plus a list of
critical properties defined for each component. An Equilibration region is a group of
cells where the initial pressure and saturation is defined. PVTi needs to know which
Equilibration region to read in if there are any composition versus depth (specified by
the ZMFVD or COMPVD keywords) tables in the ECLIPSE file. There is one table for
each of the Equilibration regions. By specifying which Equilibration region to use this
tells PVTi which table to read in.
Reading the SYSTEM section from a PVI file
1
PVTi: File | Import PVI Section | SYSTEM and select the appropriate PVI file.
PVTi searches for the required file and, if found, reads it looking for all occurrences of the
required section. If there are no RUNSPEC or SYSTEM sections in the file then no further
action is required. However, if one of more sections of the required type are found in the
file, you must select which, if any, are required. The program displays a prompt specifying
the number of sections found.
2
98
Select the section you wish to load.
Reference section
The fluid model
PVTi Reference Manual
Note
If more than one section is found, the program offers the last section as the default,
although you can read any of the sections.
Hint
If you are uncertain as to the contents of the selected section, use File | View PVI
Section to display the section to the screen.
The syntax of the external file is similar to that of ECLIPSE. The data file is free format, except
for keywords, which must start in column 1. For further information on the keywords see "PVTi
keywords" on page 167. An example of such a file for a trivial two-component CO 2 -isoButane
system is as follows:
-----RUNSPEC section:
---RUNSPEC
NCOMPS
2 /
EOS
PR /
specific number of components and the EoS
------SYSTEM section: define hydrocarbon properties and composition
---SYSTEM
---Unit conventions
UNITS
METRIC
ABSOL
FRACTION /
DEGREES
KELVIN /
---Component names (library defaults)
LNAMES
CO2
IC4 /
---Overwrite default omega values by component
OMEGAA
0.4572
0.4572 /
OMEGAB
0.0778
0.0778 /
---Initial sample composition
ZI
0.6
0.4 /
---Binary Interaction Coefficients
BIC
2
1
1
0.13 /
/
---------------END
This defines the fluid, EoS etc.
COMB, SIMULATE, REGRESS, BLACKOIL sections may now follow
See examples in Appendix C
Note the following points:
PVTi Reference Manual
Reference section
The fluid model
99
•
Any characters following ---- are taken as comments. The data is free format, apart from
keywords which should start in column 1. You can split data over lines as required. The
forward slash (/) characters terminate data for a keyword.
•
You can specify repeat counts for any item. For example 3 * 1.0 implies three values of 1.0.
You can enter defaults by specifying a repeat count alone, such as 1*, or by the early
termination of a data list with a forward slash (/).
•
You may enclose character data such as component or experiment names in quotes. This is
optional and is only strictly required when the name contains embedded spaces or nonalphanumeric characters.
Equation of State
Hint
The default Equation of State is the Peng-Robinson three-Parameter equation. This is
suitable for most requirements, so generally you do not need to set the equation of
state.
This panel allows you to choose one of five main equations of state, to specify the required
viscosity correlation, and to decide whether or not to activate editing of specific heat capacities.
The equations of state are described in "Equation of state" on page 316; the viscosity options
are described in "Viscosity correlations" on page 329 and in [Ref. 5], [Ref. 7] & [Ref. 41].
The available equations of state are:
•
Peng-Robinson
•
Soave-Redlich-Kwong
•
Redlich-Kwong
•
Zudkevitch-Joffe
•
Schmidt-Wenzel
Choosing the Equation of State
1
PVTi: Edit | Fluid Model | Equation of State...
This opens the Equation of State and Viscosity panel, which gives you radio buttons for
selecting one EoS from the following list:
2
•
PR: 2-Parameter Peng-Robinson
•
SRK: 2-Parameter Soave-Redlich-Kwong
•
RK: Redlich-Kwong
•
ZJ: Zudkevitch-Joffe
•
PR3: 3-Parameter Peng-Robinson
•
SRK3: 3-Parameter Soave-Redlich-Kwong
•
SW: Schmidt-Wenzel.
Select the appropriate equation of state.
If you select either of the Peng-Robinson equations or the Schmidt-Wenzel equation, you
must also select whether you wish to use the correction to the dependence of the Ω a upon
acentric factor. The default is the modified (third-order in ω ) Peng-Robinson form.
3
100
Check the box for Yes, or leave it unchecked for No, as appropriate (see "Equation of state"
on page 316).
Reference section
The fluid model
PVTi Reference Manual
Three-parameter extension of the EoS
The three-parameter extensions of the EOS are:
•
PR3 - Peneloux et al. three-parameter EoS
•
SW - Schmidt-Wenzel EoS (implemented as a modified PR3)
•
SRK3 - Peneloux et al. three-parameter EoS.
The PR3 EoS is the default setting.
Hint
It has been our experience that the Peneloux et al. three-parameter equations of state,
PR3 and SRK3, generally give much better predictions of liquid properties and
saturations.
They also allow you an additional set of regression parameters, namely the component
volume shifts, making for an easier match to measured data.
Viscosity correlations
The Lohrenz-Bray-Clark, Pedersen and Aasberg-Petersen viscosity models are available. Select
the appropriate viscosity model.
Note
You can re-select the equation of state or viscosity correlation at any stage. However,
the default EoS parameters for each component are dependent upon the EoS, and the
program re-initializes these if you change the EoS. Alternatively you can manually
reset the parameters to the default values at any time.
Components
PVTi: Edit | Fluid Model | Components...
Fluid model components
This option allows you to enter component names and properties. Use this option to enter new
fluid components. You enter a mnemonic and a type, which determines how the program
interprets the component.
1
Select the Names folder.
2
To enter a component, click in an empty index field.
3
Enter the mnemonic for the component and select its type.
See "Component types" on page 102.
4
Click on Apply.
5
The other folders now have information in them:
PVTi Reference Manual
•
Complete shows all the properties of all components
•
Library shows the properties that were retrieved from the internal library
•
User shows user-defined properties
•
Characterization allows definition of fluid-model properties by characterization.
Reference section
The fluid model
101
Component types
Library
The PVTi program checks this against the internal library of names. If this exists in the internal
library, it adopts the internal description. If it does not recognize the mnemonic from amongst
the set described in the previous section, you must re-enter the mnemonic name or respecify the
component as a Char or User type, see below.
User
This option allows you to define components. Enter the required properties into the panel:
critical pressure and temperature, acentric factors, etc.
You should enter the components in order of increasing molecular weight, and nonhydrocarbons before hydrocarbons:
Non-Hydrocarbons
•
H2
•
H2O
•
CO
•
N2
•
H2S
•
CO 2
Hydrocarbons
•
C1
•
C2
•
CN+
Hint
By selecting PVTi: Run | Check fluid system the fluid is re-ordered into increasing
mole weights.
PVTi allows you to input a user component even if you know only the critical temperature and
pressure. It calculates the other properties as follows:
•
from
Tb
Tc
and
Pc
- Riazi-Daubert. For further information see [Ref. 30] and [EQ 8.11],
and
Tb
- Riazi-Daubert. For further information see [Ref. 30] and [EQ 8.11],
[EQ 8.12].
•
from
Sg
Tc
[EQ 8.12].
•
Mw
from
Tb
,
Tb
and
Sg
- Riazi-Daubert. For further information see [Ref. 30] and [EQ
8.33], [EQ 8.34].
102
•
ω from
•
P
Pc
,
Tb
and
Tc
- Edmister. For further information see [Ref. 30] & [EQ 8.10].
from Macleod and Sugden. For further information see [Ref. 14].
Reference section
The fluid model
PVTi Reference Manual
•
Vc
&
Zc
- Riazi-Dubert. For further information see [Ref. 12].
Use the Update button to calculate the other properties of the component.
Characterization
If you give a characterization, you must generally specify at least two out of the following (these
are specified in the Characterization folder):
•
molecular weight
Mw
•
specific gravity
,
•
normal boiling point temperature
Tb
•
Watson characterization factor
,
•
reference temperature
Sg
,
Kw
,
K
Hint
If you have more than two of the set Mw , S g , Tb and K w , we recommend that you enter
the best two first, as the order of entry decides which pair the program selects. For
example, if you enter Mw , Tb and K w then the program uses Mw and Tb .
Note
It is possible to perform a characterization by entering just the molecular weight,
whereupon the program estimates the specific gravity from a look-up of Single Carbon
Number (SCN) groups.
You can choose from the following correlations for estimating the physical properties and
acentric factors:
Critical properties
•
Kesler-Lee. See [Ref. 10].
•
Cavett. See [Ref. 11].
•
Riazi-Daubert. See [Ref. 12].
•
Winn. See [Ref. 43].
•
Pedersen. See [Ref. 43], [Ref. 41] and [Ref. 45].
Acentric factors
•
Kesler-Lee. See [Ref. 10].
•
Edmister. See [Ref. 14].
•
Thomassen. See [Ref. 30].
•
Pedersen. See [Ref. 43], [Ref. 41] and [Ref. 45].
Note
PVTi Reference Manual
When reading in a file the critical volumes (Vc) and critical Z factors (Z c) for each
component must satisfy the relation PcVc=ZcRTc (where Tc, Pc, R are the critical
temperatures, critical pressures and universal gas constant respectively). If this is not
the case then PVTi will alter the values of the relevant critical Z-factors in order that
this relation is satisfied.
Reference section
The fluid model
103
Binary Interaction Coefficients
This option enables you to enter the Binary Interaction Coefficients (BICs) for each component.
1
PVTi: Edit | Fluid Model | Binary Interaction Coefficients...
This displays the Binary Interaction Coefficients panel.
2
Enter the Binary Interaction Coefficients for each component.
3
Alter the Cheuh-Prausnitz-A coefficient as required.
4
Click on Reset to return the interaction coefficients to default values.
Volume shifts
Note
Volume shifts are only available if you use a three-parameter Equation of State.
Use this option to enter the dimensionless volume shifts. The actual volume shifts in the
equation of state are displayed beside them.
1
PVTi: Edit | Fluid Model | Volume Shifts... .
This displays the Volume Shifts and Thermal Expansion Coefficient panel.
2
Enter the volume shifts for the required components.
3
Click on OK.
Note
If the "Temperature dependence for volume shifts" on page 147 option is set then you
can enter a value for THERMX, the thermal expansion coefficient.
Thermal properties
Note
You can only use this option if the program option "Specify/Calculate density and
molar volume units" on page 147 is switched on. It can be switched on in the Equation
of State panel (see "Equation of State" on page 100).
Specific heat capacity coefficients and calorific values for each component are the thermal
properties used in PVTi.
1
PVTi: Edit | Fluid Model | Thermal properties....
This opens the Thermal Properties panel.
2
Amend the thermal properties for the components, as required.
3
Click on OK.
LBC Viscosity Coefficients
Note
LBC Viscosity coefficients are only available if you are using the LBC Viscosity
model.
Use the option to view or edit the LBC viscosity coefficients.
104
Reference section
The fluid model
PVTi Reference Manual
1
PVTi: Edit | Fluid Model | LBC Viscosity Coefficients....
This opens the LBC Viscosity Coefficients panel.
2
View or amend the coefficients as required.
3
Click on OK.
Splitting components
This menu allows for the automatic splitting of the plus fraction into a required number of subfractions for subsequent use in a large regression or for output to a compositional simulator such
as the one in ECLIPSE.
Splitting is also used to accommodate different plus-fraction properties for different fluid
samples. This process is often known as a multi-feed split.
This option allows you to input data for splitting the plus fraction. There are three methods
available from this option for splitting the plus fraction, which must be the last component:
•
Constant Mole Fraction splitting (CMF)
•
Whitson
•
Multi-feed split or Semi-Continuous Thermodynamic (SCT) splitting
1
To choose the splitting method, select PVTi: Edit | Fluid Model | Split and select the
splitting option.
Constant Mole Fraction (CMF)
1
Specify the number of pseudo-components you require. The default is
2
Give the specific gravity and required sub-fraction split.
N frac
=
3.
By default, the program estimates the specific gravity of the plus fraction from the
reference density, if one was given, and uses a constant mole fraction split of 1 ⁄ Nfrac .
3
Specify the Whitson Alpha Factor and the Whitson ETA factor, as required.
4
Enter the Critical Props. Correlation and the Acentric Props. Correlation.
5
Give the compositions of the pseudo-components.
6
Click on OK.
Whitson or modified Whitson (Whitson)
1
Specify the first single carbon number (SCN) group to be included in the plus fraction split.
For example, enter 7 if plus fraction is C 7+ .
2
Give the molecular weight, specific gravity and the mole fraction of the plus fraction.
3
Enter the number of pseudo-components to be used after the regrouping of the Whitson
split.
For example,
N MCN
=
3
.
4
Specify the Critical Props Correlation and the Acentric Props. Correlation.
5
Select the grouping technique.
6
Choose whether you wish to plot a fingerprint of the Whitson split fractions.
7
Click on OK.
PVTi Reference Manual
Reference section
The fluid model
105
Multi-feed Split (also called semi-continuous thermodynamic (SCT) split)
1
Specify the number of pseudo-components for the split.
This value must be between two and five. The default is two.
2
Confirm the default minimum mole weight in the plus fraction (Whitson η -parameter) or
edit the data as required.
3
Confirm the default mole weight of the heaviest pseudo-component or edit the data as
required.
The default setting is twice the plus fraction mole weight.
4
Set the Critical Props. and Acentric Props. correlations.
5
Specify the group and the molecular weight of the sample’s plus fraction.
6
Amend the default names for the new components, if required.
The default names are FRC1, FRC2, etc.
Note
Note that splitting is not necessarily the opposite of grouping. Splitting the plus
fraction into two or more pseudo-components, followed by a re-grouping of those
pseudo-components back into a single plus fraction, generally results in a different set
of critical properties, etc., from those originally possessed by the plus fraction.
PNA Distribution
This splits all components heavier than the library C6 component into paraffinic (P),
naphthalenic (N), and aromatic (A) components. This is done according to the method outlined
in "The PNA distribution of heavy components" on page 394. The critical properties assigned
to the PNA components are those described in "Critical properties of PNA species" on
page 395.
Group
This menu allows for the automatic grouping of sub-fractions for subsequent use in a large
regression or for output to a compositional simulator such as the one in ECLIPSE.
This option allows you to choose components to group and perform the grouping operation. The
default scheme for grouping is to group to the default sample ZI using the mole fraction
weighting to group components. Other schemes of grouping include grouping by molecular
weight and by mixing rule, see [Ref. 44]. Also the sample to group to can be changed to any in
the defined set, or to an average of all samples.
To group components, select PVTi: Edit | Fluid Model | Group...
This displays the current component system, each component having an associated index. The
first time you enter this option, all these indices are set to 0, indicating that they do not belong
to any group.
1
To create a new pseudo component, give a new index of greater than zero to two or more
components.
2
Select the Grouping Technique.
3
Give the group or pseudo-component a new component mnemonic, if required.
Hint
106
Reference section
The fluid model
You can perform several groupings from the same original component description by
specifying the new components with ascending indices, 1, 2, etc.
PVTi Reference Manual
4
Click on the Update button to automatically display any of these new component names.
5
Click on the OK button to create the groups.
Note
Note that splitting is not necessarily the opposite of grouping. That is, splitting the plus
fraction into two or more pseudo-components, followed by a re-grouping of those
pseudo-components back into a single plus fraction, generally results in a different set
of critical properties, etc., from those originally possessed by the plus fraction.
Defining Samples
Sample names
1
PVTi: Edit | Samples | Names...
Defines sample names. Use this option to enter mnemonics for each component. You can enter
more than one sample for later use; to do this, reference each sample by its mnemonic, of up to
8 characters.
Note
Note that the mnemonic for the default sample is “ZI”, for “z initial”.
For alternative samples, you may specify a line of text to give additional information. For
example: from different depths in the hydrocarbon column, a “saved” calculated composition
from a simulation, etc.
Sample compositions
1
PVTi: Edit | Samples | Compositions....
Enter the compositions for each defined sample. PVTi ensures that they all add up to unity. If a
sample does not add up to unity, a message appears asking whether or not the program should
redistribute the difference across the components.
Sample salinities
1
PVTi: Edit | Samples | Salinities...
This option allows you to enter sample salinities. If you have entered H2 O as a component then
use this option to add the salinity of each sample.
Note
PVTi Reference Manual
This information is used in the MFLASH experiment in the "Simulation using PVTi"
on page 117.
Reference section
The fluid model
107
Mixing samples
This option allows you to form a new sample by mixing any two existing samples. You can enter
the amount of each sample to mix either as the mole fraction of the second sample in the
resulting mixture, or as a volume of gas of the second sample as a ratio to the volume of the first
sample at its P sa t or other pressure at the specified mix temperature. The latter case is useful
when considering lean gas injections into an oil.
The program produces the required mix provided that:
•
The two samples are different.
•
The amount of the second sample to mix is greater than zero.
•
The number of samples does not exceed the maximum allowed (50).
•
The name of the new sample is unique in the set.
1
To mix samples, select PVTi: Edit | Samples | Mix...
This activates the Mix Samples panel.
2
Select the Mixing Type.
3
Choose the fluid samples you wish to mix.
4
Enter the new sample name.
5
Enter the temperature with its units, and the mole fraction.
6
If you are mixing by GOR, give the GOR and the pressure for GOR oil volume
calculation
7
Click on OK.
If the sample is mixed by recombination, the GOR is taken as the stock tank GOR, the
conditions are separator conditions and the mixture is created such that the stock tank GOR
matches the required value.
Viewing samples
Sample fingerprint plot
This option allows you to generate fingerprint plots. This consists of plotting the logarithm of
the component mole fractions against the component molecular weights.
Hint
1
Fingerprint plots give an idea of the nature, that is condensate or volatile oil, of a given
fluid sample. Providing a reasonable split of the Heptanes plus is available, then a
condensate typically has straight line or down-turning slope proceeding towards the
heavier fractions, whilst a volatile oil has an up-turning slope as it usually contains
more heavy fractions.
To generate fingerprint plots, select PVTi: View | Samples | Fingerprint Plot.
This activates the Fingerprint Plot panel, which enables you to select the sample you
require to be used for the plot from a drop-down panel.
2
108
Select the sample you wish to plot and click on Apply. An example of a plot is shown in
Figure 6.2.
Reference section
The fluid model
PVTi Reference Manual
Figure 6.2 Fingerprint Plot
Sample phase plot
This option allows you to generate phase plots. This uses the equation of state model with the
current fluid description to obtain the bubble point and dew point lines. Where the two lines
meet is the critical point, at T = T c , p = pc . As part of the calculation process, an explicit
calculation is made of the position of the critical point. You can choose how many quality lines
(lines of constant vapor mole fraction) are required on the plot; this can vary between 0 and 9
(that is, 10%, 20%,..., 90%).
1
To generate phase plots, select PVTi: View | Samples | Phase Plot.
This activates the Phase Plot and Quality Lines panel.
2
Select the sample you wish to plot.
3
Enter the number of quality lines (from 1 to 9).
4
Decide whether or not to plot the Hydrate formation line.
5
Click on OK.
Hint
A default phase plot (with one quality line) can be generated by simply dragging a
sample name from the Data Tree and dropping it into the Main Plot Window.
Note
If depletion experiments or separators exist, they are plotted onto the phase plot too.
PVTi Reference Manual
Reference section
The fluid model
109
Figure 6.3 Phase plot
Sample ternary plot
This option allows you to create a ternary plot for a particular sample. The ternary plot panel
allows you to set: the sample to be plotted; the temperature and pressure for the plot; and the
grouping of the fluid components so as to create three components for the ternary plot.
1
To generate a ternary plot, select PVTi: View | Sample | Ternary Plot
2
Select the fluid sample for plotting
3
Enter a temperature and pressure.
4
Select the component groupings and the names of the grouped components.
Hint
110
Reference section
The fluid model
The default component groupings are: C1 and the non-hydrocarbons, C2-C6 and C7
and heavier hydrocarbons. This is typically the best choice, so you should only need to
change the groupings from the default in special cases.
PVTi Reference Manual
6
The third folder, Components, allows you to determine whether you enter componentbase data or not. Typical options here are for Liquid Mole Fractions, Vapor Mole Fractions
or K-values.
7
The fourth folder, Other, is used for miscellaneous observations that do not fit any of the
other categories. Currently this folder is only used by the Constant Volume Depletion
experiment for the Final Liquid Mole Fraction. When other experiments are being entered,
this folder does not appear.
8
Click Apply.
9
A customized form is now created, with the same folders as described above. Now the
folders contain data-entry fields and tables for observations. Once the data have been
entered, click on Apply to submit the data and create or edit the experiment.
10 Finally, Close becomes active and can be used to close the panel
Data requirements for the experiments
Flash calculation
For this experiment you must define the pressure and temperature of the flash.
The program performs a stability test and establishes the number of phases present prior to the
flash calculation.
Note
The gas-oil ratio reported by the calculation is defined as gas volume at standard
conditions divided by liquid volume at flash conditions. The gas volume is obtained
using a Z -factor of unity.
Bubble point pressure
For this experiment you must enter the temperature at which the bubble point is required.
Note
If the temperature is such that no bubble point can be found (above the critical
temperature) the program returns a warning message.
Dew point pressure
For this experiment you must supply the temperature and choose between normal or retrograde
dew points. The default dew point is retrograde.
Note
If the temperature is such that no dew point can be found (above the critical
temperature) the program returns a warning message.
Constant composition expansion
For this experiment you must specify a temperature and a series of pressures. Additionally you
must specify whether the fluid is oil or gas. You do not need to give a value at saturation
pressure.
118
Reference section
Simulation using PVTi
PVTi Reference Manual
Hint
You can apply this experiment to a liquid (bubble point) or vapor (dew point) system.
The program tests for both possibilities. It is also possible to perform a constant
composition expansion on a true one-phase system (SIN), such as an (dry) injection
gas above its cricondentherm.
Note
When obtaining relative volumes the program uses saturation volume as a
normalisation volume, if one exists, or the volume at the highest pressure, if not.
Constant volume depletion
For this experiment you must specify a temperature and a series of pressures. You do not need
to give a value at saturation pressure.
Hint
You can apply this experiment to a liquid (bubble point) or vapor (dew point) system.
The program tests for both possibilities. It is not, however, possible to apply this
experiment to samples that are above the cricondentherm.
Note
The relative volume reported by the program is the fraction of the cell filled with liquid
at the end of the constant volume step, that is after the original volume has been
restored by removing vapor.
Differential liberation
For this experiment you must specify a temperature and a series of pressures. You do not need
to give a value at the bubble point. PVTi provides this pressure point.
The program also provides automatically the last step in the differential liberation process, the
reduction to standard conditions. However, the program does not provide the pressure point at
standard pressure (usually 14.7psia) and at reservoir temperature and the user must enter this for
the final stage.
Note
You may only apply this experiment to a liquid (bubble point) system.
Hint
The relative volume reported by the program is the ratio of the oil volume at each step
to the oil volume at the final (standard conditions) step.
Note
There are alternative definitions of the GOR and the relative oil volume available using
the program options "Definition of GOR in Diff. Lib." on page 148 and "Definition of
Oil relative volume in Diff. Lib." on page 149.
Swelling test
A swelling test consists of adding increasing amounts of a lean gas to a reservoir fluid and
determining the swelling of the mixture relative to the original fluid composition.
For this experiment you must specify:
PVTi Reference Manual
Reference section
Simulation using PVTi
119
1
The nature of the original fluid type, OIL or GAS.
2
The composition of the lean gas to be added.
3
The reservoir temperature.
4
A set of either mole percentages of gas in the mixture or GORs (the volume of gas at STC,
that is 14.7 psi and 60° F , per volume of oil at original saturation pressure or other specified
pressure).
Separators
Separators consist of a set of connected equilibrium flashes at user prescribed pressures and
temperatures.
For this experiment you must specify:
1
The composition of the feed stream from the defined sample mnemonics.
2
A number of stages (up to seven) for which you must give a pressure and temperature.
Additionally, you must connect the vapor and liquid outputs of each stream to some subsequent
stream. The default routing is to connect the liquid output of stage (j) to stage (j+1), and to take
the vapor output to stock tank conditions (as defined by the STCOND keyword or by the
Standard Conditions menu option under OPTIONS).
Note
A stage output can be fed back to any previous stage though not back to the current
stage. No stock tank stage is defined automatically, and whereas it is customary to
quote vapor properties at stock tank conditions, liquid properties will be quoted at the
“final stage” conditions. Therefore, if liquid properties at stock tank conditions are
required, this should be the final (additional) stage which must be defined by the user.
For example if we have a separator with 3 stages with the last stage being stock tank
conditions, then a liquid FVF at stage 1 of the separator will be the volume of liquid
divided by the final liquid volume (stock tank conditions in this case) after flashing the
liquid feed of stage 1 through the remaining 2 stages of the separator chain.
Hint
The "Definition of Oil relative volume in Diff. Lib." on page 149 program option
allows you to quote GORs as volume of gas at standard conditions per volume of stock
tank oil as opposed to the default calculation of volume of gas at standard conditions
per volume of separator liquid at separator conditions.
The program can calculate oil formation volume factors, that is the volume of reservoir fluid at
initial or bubble point conditions per stock tank volume (SRELV) and, by separator stage,
volume of separator liquid at separator conditions per stock tank oil volume (ORELV).
To use this option tick the box in the panel or use the FVFREF keyword in batch mode.
Variation of composition and pressure with depth
It is well known that composition varies with depth in a reservoir.
For this experiment you must specify:
120
1
A reference sample composition (from the currently defined sample mnemonics).
2
A reference depth, pressure and temperature for the sample.
3
A set of depths above and/or below the reference depth, at which you wish the program to
calculate the composition and pressure.
Reference section
Simulation using PVTi
PVTi Reference Manual
If during the increment up and/or down, either a genuine gas-oil contact is found or a transition
from gas to oil (or vice-versa) without passing through a contact (a “critical” transition), then
the program reports this depth.
Note
The assumptions made in the performance of this experiment, that there are no
asphaltenes and that the reservoir is in thermal, gravitational and diffusive equilibrium,
are probably not achieved in any real reservoir. However, despite these reservations,
this is a useful test of the depth-variation of a particular fluid.
Vaporization test
This is a somewhat specialised test performed for gas-injection on reservoir fluids, but in fact it
is rather similar to a swelling test.
For this experiment you must specify:
1
The composition of the reservoir fluid and injection fluid from the currently defined sample
mnemonics.
2
The reservoir pressure and temperature
3
The number of moles of injection gas to be added to the reservoir fluid.
Multiphase flash calculation
The inputs required for the multiphase flash experiment are the same as for the usual two-phase
flash experiment ([Ref. 36]). For this experiment you must define the pressure and temperature
of the flash. The program performs a stability test and establishes the number of phases present
prior to the flash calculation.
Note
The gas-oil ratio reported by the calculation is defined as gas volume at standard
conditions divided by liquid volume at flash conditions. The gas volume is obtained
using a Z -factor of unity. Note also no facility currently exists for comparing these
against observed values.
Note
If the sample you select for the experiment contains water, you should enter the salinity
in the PROPS section.
Saturation pressure calculation
This is essentially the same as the bubble and dew point calculations. For this experiment you
must enter the temperature at which the saturation point is required.
The calculation is particularly useful if you have no a priori information about whether the
saturation point is bubble or dew.
Note
PVTi Reference Manual
In the case of the dew point, program returns the retrograde (highest pressure) dew
point.
Reference section
Simulation using PVTi
121
Saturation temperature calculation
For this experiment you must specify the pressure. Since there are generally two saturation
temperatures (one from each side of the phase envelope), you must also specify which solution
is required - lower or higher.
Critical point calculation
This is a convenient way of obtaining the critical point of a sample, without generating a full
phase envelope. Enter the sample name for this experiment.
First contact miscibility pressure calculation
This calculation returns the lowest pressure at which the samples are directly miscible,
regardless of the proportions in which they are mixed. The method used to determine the
minimum pressure is described in the paper by Jensen and Michelsen, [Ref. 39]. For this
experiment specify the temperature and the names of the two samples.
Multiple contact miscibility pressure calculation
This calculation determines the lowest pressure at which two samples (one oil, one gas) are
always miscible (regardless of their relative proportions) after repeated contacts between them,
when only one of the samples is affected at each contact. When the sample affected is the gas,
this simulates a one-cell vaporizing drive. If the oil is affected each time, this mimics a one-cell
condensing driveways method used to determine the minimum pressure. This case is also
described in the paper by Jensen and Michelsen, [Ref. 38]. For this experiment, specify the
temperature and the names of the two samples. Give the drive to simulate.
Multiple contact test
This experiment simulates the multiple contact test where a series of flashes are performed on
mixtures of reservoir oil and injected gas.
For this experiment specify:
1
The oil and gas samples
2
The temperature and pressure of the test
3
The drive to simulate (either condensing where the remaining oil is kept after each flash
and contacted with the initial gas sample, or vaporizing where the remaining gas is kept
after each flash and contacted with the original oil sample)
4
The fractions of remaining oil/gas to be contacted with the original gas/oil at each stage.
Hint
You can use this experiment in the REGRESS section. For further information see
"Regression in PVTi" on page 126.
Defining Observations
Observations can be defined at the same time as the experiment; see "Defining Experiments" on
page 117.
1
PVTi: Edit | Observations...
This opens the Define Simulate Observations panel.
122
2
Choose the index of the experiment
3
Select abbreviation for the observation to be entered
Reference section
Simulation using PVTi
PVTi Reference Manual
4
Enter the data for this observation
5
If you are entering data for regression purposes, give weightings, either individual or
global, for the observation types.
The observations available vary with experiment type, but will be from the following set:
Table 6.2
Observation data
Abbreviation
Observation
Liquid Z-Factor
Liquid Z -factor
Vapor Z-Factor
vapor Z -factor
Liquid Density
Liquid density
Vapor Density
Vapor density
Liquid Mol. Wght. Liquid molecular weight
Vapor Mol. Wght
Vapor molecular weight
Liquid Visc.
Liquid viscosity
Vapor Visc.
vapor viscosity
Liquid Sat.
Liquid saturation
Vapor Sat.
Vapor saturation
Vapor Mol. Frac.
Vapor mole fraction
Sat. Pressure
Saturation pressure: gas - pdew , oil - p bub
Sat. Temperature
Saturation temperature: not currently available
Gas-Oil Ratio
GOR: SEPS - gas (STC)/oil (stage/STC); DL gas (STC)/oil (STC/ p sat )
Relative Vol.
Relative volume (SWELL = swelling factor)
Total Gas-oil ratio
Cumulative separator GOR: (Gas at STC/final stage Oil)
Ternary Plot
Ternary Plot (Multi-Contact Test and plotting only)
Mole. wght. plus
Mole weight of plus fraction (COMB Mat. Bal.)
Rel. oil sat.
Relative oil saturated volume (B o ( p bub) in DL)
K Values
K -values
Liquid mol. frac.
Liquid mole fraction
Vapor mol. frac.
vapor mole fraction
Total mol. frac.
Total mole fraction
Spec. grav. plus
Specific gravity of plus fraction (COMB Mat. Bal.)
Moles Recov.
Moles recovered from depletion experiment (CVD,DL)
Liquid mol. vol.
Liquid molar volume (specific volume)
Vapor mol. vol.
vapor molar volume (specific volume)
Final mol. wght.
liq. plus
Mole weight of liquid plus fraction (COMB Mat. Bal.)
Final spec. grav.
liq. plus
Specific gravity of liquid plus fraction (COMB Mat. Bal.)
Final liq. mol. frac. Liquid mole fraction of final stage of CVD (COMB Mat. Bal.)
PVTi Reference Manual
Total rel. vol.
Total (oil and gas) relative volume (DL)
Oil rel. vol.
Oil relative volume (DL, SEPS, vapor) (also see RVSAT)
Gas Gravity
Gas gravity (Differential Liberation)
Reference section
Simulation using PVTi
123
Table 6.2
Observation data (Continued)
Abbreviation
Observation
Gas FVF
Gas formation volume factor (DL)
Gas Vol. Ext.
Gas volume extracted (at STC) (DL)
2-phase Z
Two phase Z -factor (CVD)
Oil rel. FVF
Oil FVF from p init ⁄ p bub to p stock (SEPS)
Note
Note that not all the observed data types are available for all experiments.
Running a simulation
Note
1
Simulations are automatically run on creation, so the results are immediately available.
PVTi: Run | Simulate
When the simulation is complete the program displays a text module detailing the success
or otherwise of the runs. The PVTi main display window showing the experiment results
will resemble the following:
CCE :
Constant Composition Expansion
Soave-Redlich-Kwong (3-Parm) on Z1
Lohrenz-Bray-Clark Viscosity Correlation
Density units are
KG/M3
Viscosity units are
CPOISE
Surface Tension units are
DYNES/CM
Deg K
Specified temperature
377.5944
Liq Sat calc. is Vol oil/Vol Fluid at Sat. Vol
------------------- ----------------------Rel Volume
Pressure
Inserted ----------------------BARSG
Point
Observed Calculated
------------------- ----------------------344.739
0.9189
0.9485
310.265
0.9278
0.9565
275.791
0.9379
0.9652
241.317
0.9492
0.9750
199.948
0.9623
0.9882
193.053
0.9651
0.9906
186.159
0.9681
0.9930
179.264
0.9711
0.9955
Hint
124
-----------Vap Mole Frn
-----------Calculated
------------
-----------Liq Density
-----------Calculated
-----------682.4368
676.7593
670.6133
663.9241
655.0453
653.4620
651.8460
650.1961
PVTi recognizes which experiment simulations are up to date and then only performs
necessary calculations. This means that to view the simulation results you should
always use PVTi: Run | Simulate.
Reference section
Simulation using PVTi
PVTi Reference Manual
Hint
If you click on an experiment in the sample-tree using the right mouse button, and
select Report... from the drop-down menu, you can see the report for that experiment
on its own.
Plotting simulation results
In addition to the simulation results tables, the results of simulations can be plotted. There are
two ways to do this.
Firstly, to view the comparison between the simulated results and the observations, simply drag
the appropriate observation from the Data Tree and drop it into the Main Plot Space.
Secondly, you can use the observation editor to plot any simulated quantity, not just those for
which there are observations. For information on the observation editor see "Defining
Observations" on page 122.
PVTi Reference Manual
Reference section
Simulation using PVTi
125
Regression in PVTi
Introduction
Performing a regression
To perform a regression you must specify:
•
The experiments to be used in the regression. You can choose from the experiments
mentioned in "Defining Experiments" on page 117.
•
The weighting for the observations associated with those experiments. You can use most of
the observations given in a laboratory experiment as observations to match against
predicted data.
•
The Equation of State parameters you wish to vary to match predicted to observed
quantities. Most of the Equation of State parameters are available as regression variables.
Note
The time taken for the regression operation rises rapidly with the number of variables
chosen, and the use of the minimum possible set is suggested. That said, any
combination of critical point data, Ωa and Ω b values, acentric factors, binary
interaction coefficients, δij and volume shift parameters (if the PR3 or SRK3 forms for
the Equation of State are being used) may be chosen to be modified. There is a
maximum total of 50 regression variables.
Regression function
The regression function to be minimized is the normalized root mean square (RMS) error of
predicted experiment results to the given (weighted) observed experiment results. See "Details
Folder" on page 131 for a description of the RMS value used.
Note
In order to run the regression, there must be at least as many observations as chosen
regression variables.
Regression Panel
1
To open the Regression panel select PVTi: Run | Regression...
2
Use this menu to set up and perform regression. To open this menu, select PVTi: Edit |
Regression
Variables
The Variables section has the following options:
•
Normal (component properties and BICs)
Normal variables are individual fluid component properties and binary interaction
coefficients. For further information see "Defining regression variables..." on page 127.
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Regression in PVTi
PVTi Reference Manual
•
Special (MW of characterized components etc.)
The special variables available depends on the project settings and the fluid model
properties. Typical special variables are the mole weight of the plus fraction or the CheuhPrausnitz coefficient for binary interaction coefficients. See "Setting special variables" on
page 129.
•
PVTi Selects
This sets up the regression variables according to the rules given in "Physical selection of
regression parameters" on page 386.
The two buttons are:
•
Variables... Opens a panel specific to the selection of variable types (see above).
•
Limits... Sets limits on regression variables. For further information see "Setting regression
limits" on page 129.
Report
The Report section has the following buttons:
•
Regression: Opens the Regression Report panel. See"Regression Report" on page 130.
•
Simulation: Opens the simulation report of all experiments.
Regress
The Regress section is for running regressions. The buttons in this section are:
•
Run: Perform regression. For further information see "Performing a regression" on
page 130.
•
Accept / Reject: Accept or reject the last regression. For further information see
"Accepting or reject regression results" on page 130.
Additional Information
Defining regression variables...
Use this option to define/re-define the set of variables for use in the regression. There may be
two sets of variables available for use in regression, depending on the state of the "Program
options" on page 145 and whether modified Whitson splitting (SCT) has been used on the plus
fraction. The two sets are denoted normal and special.
•
The normal variables are the component dependent ones, that is variables such as critical
properties, acentric factors, etc.
•
The special variables are system-wide or multi-component variables such as the thermal
expansion coefficient or the Cheuh-Prausnitz A -factor for binary interaction coefficients.
Setting normal variables
There are two panels for setting normal variables.
Use the first panel to define the EoS parameters, the parameters for the LBC viscosity
correlation and the volume shifts for the currently defined Nc components.
PVTi Reference Manual
Reference section
Regression in PVTi
127
1
Enter integers for the EoS parameters:
a
Pc
b
Tc
c
ω
d
Ωa
Hint
2
Enter integers for the LBC viscosity parameters:
a
Ωb
b
Vc
c
Vc
Hint
3
If you wish to vary a given EoS parameter, say Tc , of two or more components as
separate independent quantities, you should give them different values. For example
1,2,..., etc.
If you wish to vary the parameters as one or more groups of variables, you should give
the required group members the same integer. This may be particularly useful when
trying to vary V c values to match to viscosity data using the LBC correlation, for
example.
Enter integers for the volume shifts:
a
PR3
b
SRK3
Note
All of these data fields can take an integer value, 0,1,2,..., and so on. The default of
zero (or blank/null field) implies that the particular component’s EoS parameter is not
to be used in any subsequent regression.
Use the second panel to define the status of the lower half of the (symmetric, zero-diagonal)
matrix of binary interaction coefficients.
Note
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Reference section
Regression in PVTi
Note that the rules regarding choice of groups for binary interaction coefficients are
slightly different in that groups may be specified down columns or along rows of the
lower half matrix but not both.
PVTi Reference Manual