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

2

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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10

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

16

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

Simulation of MEQ

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Reasonable MwPromising to use for reservoir characterization

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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Acknowledgements

• RPSEA (Research Partnership to Secure Energy for America)

• EPA (U.S. Environmental Protection Agency)

Thank you

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