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Product Suite
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Classification of Unconventional Gas and Oil
Advanced Processes & Thermal Simulator
• Shale gas and oil
Compositional & Unconventional Reservoir Simulator
• Tight gas and oil
Three-Phase, Black-Oil Reservoir Simulator
• Natural gas from coal (NGC/CBM/CSG etc.)
Sensitivity Analysis, History Matching, Optimization & Uncertainty
Analysis Tool
• Gas hydrates or Methane hydrates
Integrated Production & Reservoir Simulation
Intelligent Segmented Wells
Phase Behaviour and Fluid Property Application
Pre-Processing: Simulation Model Building Application
Post-Processing: Visualization &Analysis Application
Characterization of Tight Formations
Introduction to Unconventional Reservoirs
Source: Canadian Society for Unconventional Resources:
http://www.csur.com/sites/default/files/Understanding_TightOil_FINAL.pdf
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Unconventional Gas and Oil Development
Simulating Unconventional Assets
• As conventional gas and oil resources are becoming depleted, it has become a
necessity to produce from unconventional resources in order to meet demand
• From 2008 to 2018, production from tight and shale plays in the United States
has increased 10 X
• In today’s economy, with lower oil and gas prices it has become extremely
important to be able make informed decisions with the greatest economic
benefit
• Strict cost control is an overriding concern in most operations, yet there are
tangible economic benefits for operators who make the effort to model
reservoir performance before they drill. • Spend a ½ day in the Library rather than waste $1mm in the field
Simulating Unconventional Assets
Example: Fracture Gap
• Despite a current oversupply in the market, tight resources are still
required to meet demand
• Need to fully understand the underlying physics that governs the flow through
tight formations.
• Determine optimal well spacing and optimal fracture size & spacing.
• Size fraces to avoid fracture hits
• Crucial to identify the reservoir parameters that will have the most impact on
project economics.
$250k per frac stage, 6 to 20 stages per well
$1.5MM to $5MM per well
0.8bcf * $3.00/mcf * 1,000,000 = $2.4MM lost
SPE 119899 : 69% of 389 wells completed in the Barnett
study have less than a 10% internal rate of return !
400 ft gap
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Shale Reservoir Properties
• Generally Naturally Fractured
▪ Low permeability fractures
• Matrix extremely low permeability
▪ Range from micro to nanodarcies
• Pore Diameters are extremely small
▪ Range from micro to nanometres
Reservoir Characteristics and Hydraulic
Fracturing
Conventional Gas
Shale Gas
Shale Gas
Tight Oil
• Natural Gas Stored in Organic rich rocks
• Shale acts as both source / reservoir rock.
• Gas in shales is found in two forms:
▪ Free Gas - Gas stored in matrix pore volume
• Tight oil formations are heterogeneous and vary widely over relatively short
distances.
•
The amount of oil recovered from single horizontal well may vary, as may recovery within
a field or even between adjacent wells.
• The API of oil in tight reservoirs can vary greatly from 20 to 50.
▪ Adsorbed Gas - Gas is attached or Adsorbed onto solid organic material
in the shale
• Tight reservoirs which contain oil with low gas solution sometimes cannot be
economically produced
• Drive mechanism is solution gas drive
Shale
Shaly Siltstone
Shaly Sandstone
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Hydraulic Fracture
Treatments
Pumping Phase
Tight Oil Properties
• Permeabilities range from less than 0.1 nD to 1 mD (SPE 167146) but are
typically in the range of 1e-3 to 1mD for tight oil
Hydraulic fracture
resumes in SHmax
direction at natural
fracture tip
• Tight Oil Reservoirs can be modelled as dual permeability or single porosity
• Porosity-permeability cross plots show that in general permeability increases
with porosity, but the relationship is not strong
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N
Reactivation of
natural fractures
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1
1
0.1
Trace of part
of horizontal
wellbore with
perforation
0.1
0.01
0.01
0.001
0
0.05
0.1
0.15
0.2
0.25
0
0.02
0.04
0.06
0.08
0.1
J.F. Gale, UT, 2008
~ 500 ft
Developing an Unconventional Asset
• Horizontal wells: To maximize contact area
• Multi-stage fracturing: 10-30 fractures per well
Modelling Unconventional Reservoirs and Hydraulic Fractures
Physics to be Modelled
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Modelling Unconventional Resources: Physics to be Modelled
Modelling Unconventional Resources: Physics to be Modelled
Reservoir Description
• Matrix – intrinsic porosity & absolute permeability
• Natural Fractures – dual permeability representation with effective fracture
porosity & effective fracture permeability
• Propped Fractures – explicitly modelled as part of matrix
• Pore Volume Compaction/Dilation – via constant compressibility and/or
compaction/dilation tables
• Momentum Transfer – Darcy and Non-Darcy (Turbulent) Flow, the latter in
the propped fractures
PVT
• Black Oil (IMEX) – for black oil and dry gas
• EoS – for wet gas, gas condensates (lean and rich) and volatile oil
Simulation Model Gridding
• Logarithmically-Spaced, Locally-Refined, Dual Permeability (LS-LR-DK or Tartan) Grids
surrounding the propped fractures
‒ For modelling transient multiphase fluid flow (and heat, if desired) from matrix to natural
fractures & from matrix to propped fractures
‒ For modelling non-Darcy flow inside the propped fractures
Simulation Model Initialization
• Initializing the propped & natural fracture network with water
‒ For modelling flowback of injected fracture fluid
Modelling Unconventional Resources: Physics to be Modelled
Adsorbed components
• Gas phase only – for mostly methane tight/shale gas
• Multi-component – for multi-component gases (w/impurities) & liquids
Modelling Unconventional Reservoirs and Hydraulic Fractures
Diffusion
• Multi-component gas
• Miscible Gas Injection EOR
Modelling Natural Fractures
Rock Physics
• Tight rock Rel Perm & Cap Press in matrix
• Straight Line Rel Perm & no Cap Press for propped & natural fractures
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Natural Fracture Modelling in CMG
• Reservoir mainly made of low porosity
rock called matrix
• Natural fractures are high permeability
flow channels that can contribute
significantly to the flow
• For simulation, each grid block will be
composed of MATRIX part and a
FRACTURE
Modelling Unconventional Reservoirs and Hydraulic Fractures
Hydraulic Fracture Modelling
Natural Fracture Channel
Matrix
Natural Fracture Modelling in CMG
Standard dual-porosity model
Fracture Model Scenarios
MINC model
Dual-permeability model
Subdomain partitioning
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Fracture Model Scenarios
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Modelling Hydraulic Fractures
• In the reservoir, the hydraulic fractures have widths in the magnitude of a
couple millimeters with very high intrinsic permeabilities
• To model this, very fine gridding would be required
• With more grid blocks, runtimes will become very large
• To reduce the number of blocks and the runtime, the fracture can be
pseudoized to a width of 2 ft
• Permeability of the hydraulic fractures is replaced with an effective permeability
• LS-LR-DK Method (SPE 132093)
• Logarithmically Spaced, Locally Refined, Dual-Permeability
CMG’s LS-LR-DK (i.e. TARTAN) Grids for Modelling Planar & Complex Geometry
Propped Fractures
Modelling Hydraulic Fractures
• Conventional fractured reservoirs typically can be modelled using
standard Dual Porosity/Permeability or MINC Models
• Due to the extremely slow pressure transients in shales and other
tight reservoirs, flow cannot be accurately described using these
standard models
• Hydraulic Fractures need to be explicitly modelled to model the
flow behavior
Planar fractures in SRV
Complex fractures in SRV
• To model the transients accurately
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Propped Frac Gridding
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Effective Hydraulic Fracture Perm
Qoriginal=Qnew
Create LS-LR-DK grids around
fractures automatically
(Kfwfhf/μ+Kmwmhm/μ)*(dP/dx)=Keffweffhf/μ*(dP/dx)
Single Plane Geometry
Kfwf+Kmwm=Keffweff
Keff=Kfwf /weff+Km
Complex Geometry
Parameterizing Propped Frac Properties
Local Refinement
• To correctly capture the transient effects around the hydraulic fractures,
fine gridding of the matrix is required
Propped Frac Properties:
Half-length, Width, Perm, Spacing,
Height & Perm Gradient
Stimulated Natural Frac Properties:
Width, Perm
• Local Refinement is used around the fractures to have more accuracy
where it is needed
• Evenly spaced gridding has too much accuracy far away from the
fractures where it is not needed and not enough accuracy close to the
fracture
• Logarithmic Refinement solves this issue by having more refinement
close to the fracture where it is needed and less refinement far away
from the fracture
SRV Size & Shape:
# MS events per gridblock
MS Moment Magnitude
MS Confidence Value
?
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