Post on 04-Apr-2018
TOUGH+ROCMECH for the Analysis of coupled Flow, Thermal, Geomechanical and Geophysical Processes — Code Description and Applications to Tight/Shale
Gas Problems
Jihoon Kim, George J. Moridis , John Edmiston, Evan S. Um, Ernest Majer
Earth Sciences Division, Lawrence Berkeley National Laboratory
24 Mar. 20141
Tight & Shale Gas
• One of the potential energy resources– (500~1000 Tcf)
• Low matrix permeability– Naturally fractured – Hydraulic fracturing
• Fracture: highly deformable– Pore volume & permeability closely related to
geomechanics• Rigorous modeling in coupled flow
and geomechanics required
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Outlines
TOUGH+ROCMECH, T+Mo ROCMECHo Coupling to TOUGH+
Shale/tight gas Simulationo Hydraulic Fracturingo Electromagnetic (EM) simulationo Microearthquake(MEQ) Simulationo Failure along the vertical wello Failure during gas production
Ongoing Research
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ROCMECH
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• Written in Fortran 95• Employ the finite element method• Plasticity ModelingShear failure, (Mohr-Coulomb model)Tensile failure, (Node splitting method)
• Plane Strain 2D & Full 3D versions• Sequentially coupled to TOUGH family
codes (flow simulators)
Input Files
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• RM_Input_3D (_2D)Number of unknowns, Materials, Monitoring points, other
control parameters
• ELEME_NODE_3D (_2D)Connectivity of nodes & elements in FEM, Coordinates,
Initial total stress, boundary conditions
• IntFACE Pres Sat T 3D (_2D) Connectivity between flow & geomechanics, Initial
pressure & saturation, Assignment of the materials
• Flow_MINC_CONNE, MINC ROCK Connectivity for the multiple continuum approach,
Assignment of the materials
Why a Sequential Method?
Desirable from a software development perspective Fully coupled method: extremely expensive ($$) &
Computational efficiency issues
Making use of existing robust simulators(e.g., mechanical and flow simulators)
Implement interface code only
Competitive with fully coupled methodMust deal effectively with issues related to accuracy,
stability, convergence Fixed-stress sequential method
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TOUGH+ROCMECH (T+M)
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• Flow Problem: Finite Volume Method (FVM)• Geomechanics: Finite Element Method (FEM)
Mixed formulation
P
u
nodea at nt displaceme :u
center grida at pressure :P
Space
Time• Fully implicit time discretization
Sequential Approach
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Flow
Geomechanics
Geophysics(MEQ, EM)
Pressure, Saturation, etc.Update porosity, Permeability,
Displacement, Strain, Failure zones, etc…
Coupling
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1 1 1 1,( ) 3
nn n n n n n n nl l l ll l l l T l l l l v v
l s l
nl p
bp p T TK K
c
0, ,p f p sk k
PermeabilityTensile failure:
Shear failure:
Porosity: Fixed-stress split
,3'
11σεCσ TK
pbpb drT
E
JJee
Stress-pressure-temperature
Cubic law, when np=3.0)(12
gGrad www
n
cw pHaQp
Higher than shale permeability
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Shear Failure
'm
'1
'3
'2
Drucker-Prager model
Mohr-Coulomb model
Hydrostatic axis
'mMohr-Coulomb model
Cohesion
Conventional return mapping for shear failure
Nonlinearity in geomechanical moduli
0cossin'' fhfmm cf
Vertical Tensile Fracturingyy
xy
z
Horizontal well
xy
z
Fracture plane
Fracture Node splitting
Fracture
z
Traction boundary
z
By symmetry
No horizontal displacement Traction boundaryFracturing
Nonlinearity from the boundary condition
cnstc Tttt 2'2'2'2'
st
ttt
nt
Traction
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Code Verification (T+M)
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Numerical and analytical results are in good agreement.
Poromechanical effect
2D Plane strain geomechanics
Fracture propagations
Static fractures
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Shale/tight gas Simulationo Hydraulic Fracturingo EM simulationo MEQ Simulationo Near-well failureo Failure during gas production
Fracturing by Water Injection
Stimulated zone
Main Fracture
Small & local fractures
Injected Water
Reservoir gas
Open
Closed
Fracture
Water saturation0 . 0 wS
Within created fractures, gas & water can coexist.14
Coupled flow & geomechanic simulator(TOUGH-ROCMECH ,T+M)
We employ rigorous coupled flow & geomechanics modeling:
• Thermo-poro-mechanics (two-way coupling)
• Dynamic multiple continuum approach • Tensile & shear failure• Leak-off to the reservoir formation from
full 3D flow simulation
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1. Hydraulic Fracturing(Horizontal Well)
Horizontal well
xyz
Fracture plane
Fracture
Traction boundary
12.0E GPa
0.3
17.10GP MPa
58.75oT C0 78.76 10pk D
10.0cT MPaz
Investigate fracture propagation for shale gas reservoirs
40 /injQ kg s
hS VS HSMPa3.23 MPa1.29 MPa4.36
GP
MPa1.17
Fluid Injection
1.0, iwSHS
hS
VS
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150m
150m
66m
A fracture grows up and down stably.Fracturing occurs along the fracture tips.
60s 500s
1200s 1600sHW
Fracture Propagation
HW
Time (s)
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Water Displacement (I)
Water is only partially saturated within the fracture.
Water
Gas
60s 500s
1200s 1600s
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Water displacement (II)
Aperture (cm)
Sw
PressureTopBottom
60s 500s
1200s 1600s
Fracture propagation is faster than water movement19
Pressure, Aperture, Displacement
Fractured Nodes
Fracture Opening (m)
Uplift (m)
Pressure (Mpa)
Saw-tooth (oscillatory) pressure, fracture opening, displacement
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Leak-off of WaterGas Saturation 1600s
Damaged Zone Second layer in the y direction
Significant leak-off of water might occur.
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Motivation of EM Geophysics
• Electromagnetic(EM) geophysical methods:• Highly sensitive to fluid saturation and chemistry in
new/existing pore spaces.• Illuminates migration pathways of the injected fluids and
proppants. • Complements micro-earthquake (MEQ) fracture
mapping.
Joint analysis of flow, geomecahnics, MEQ & EM:better understanding of fractured reservoirs
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Saturation & Electric conductivity
Water saturationElectrical conductivity Nanofluid, σ=1000 S/m, µr=1
Electrical conductivity(brine: σ=3.3 S/m, µr=1)
200s
1600s
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Vertical Crosswell EM
1600s1200s500s200s
Source position: z=-1350 mNanofluids can enhance EM signals significantly.
Nanofluid (σ=1000 S/m, µr=1) Brine (σ=3.3 S/m, µr=1)
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Horizontal Crosswell EM
1600s1200s500s200s
Brine (σ=3.3 S/m, µr=1)Nanofluid (σ=1000 S/m, µr=1)
Source position: z=-1440 mNanofluids can enhance EM signals significantly.
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2. Hydraulic Fracturing(Vertical Well)
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10.0E GPa0.3
28GP MPa0 78.76 10pk D
54VS MPa0.8H VS S0.45h VS S
Vertical well
xyz
Fracture plane
Fracture
90 /injQ kg s
Fluid Injection
HShS
VS10.0cT MPa
5cT MPa
160m
5.0cT MPa
600m
300m
120m
0.3wiS
Hydraulic Fracturing
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Little oscillatory
The fracture propagates horizontally and downward due to strong overburden.
Injection point
Seismic Moment Tensor
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)( , pqqppqkkpqpqpq uvuvuvmdmM
)0,1,0(v
),,( zyx uuuu
displacement
0 2LM M
10 0log 16.1 4.665 ( )1.5wMM N m
New fractured area
3. Vertical Well instability
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HShS
VS
Injection well (open)
3D Simulation domain
5m
150m 90m
9m
Injection well (cemented)
Same previous reservoir conditions
Constant Bottom hole pressure,30MPa
0 0.05 0.1 0.15 0.20
0.05
0.1
0.15
0.2
Well casing Cement-casing contact
Cemented area
Reservoir
m
Well Failure(Shear Failure along the Well)
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HShS
VS
Failure area
MPac cmh 10
cement ofcohesion :cmhc
areacontact in cohesion :cthc
MPac cth 10 MPac ct
h 5 MPac cth 1
Complete cementing
Incomplete cementing
Incomplete well cementing causes significant well failure while complete cementing does not
At 1800s
4. Gas production2D plane strain
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Long fractures with horizontal well in 3D 2D plane strain geomechanics (vertical or horizontal fractures)
20m vertical fracture
10m horizontal fracture
Elasticity Prediction
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Initial Pressure and total stress: 68.5MPaConstant Bottom Hole Pressure: 20MPa
MPacradGPaE hf 4,5.0,22.0,28.1
Potential Failure
.1sin
cossin''2
f
fhfmm c
Weak reservoirs
Plasticity: Shear Failure
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Dynamic permeability changes flow patterns & geomechanical responses significantly.
Case 1:Vertical Fracture Case 2: Horizontal Fracture
7day 30day
45day 75day
7day 30day
45day 76day
Secondary Fracturing & Enhanced Permeability: Enhanced Productivity
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Case 1: Vertical Fracture Case 2: Horizontal Fracture
200.8
B
B
P MPab
301.0
B
B
P MPab
Low effective stress
Significant secondary fracturing might not occur.
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Different Plastic ParametersCase 1: Vertical Fracture Case 2: Horizontal Fracture
Significant secondary fracturing can occur for 300.35
B
f
p MParad
Secondary fracturing depends on flow-geomechanics parameters and production scenarios.
Summary• Developed an integrated Coupled Flow-
Geomechanics-Geophysics simulator.• Fracture propagates faster than the injected
water does.• Water & gas coexist within the stimulated zone.• Crosswell EM is sensitive to migration pathways
of injected water.• MEQ simulation is a promising tool for reservoir
characterization.• Complete cementing job is required to avoid
potential failure along the vertical well.• Secondary failure can occur even during gas
production for weak reservoirs.37
Ongoing Research in Geomechaniccs
• Parallel Codes• MEQ in various failures
– Near the stimulated zone, Fault, Strong capillarity
• Chemo-Thermo-Poro-Mechanics• Large deformation (Finite Strain)
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