Jihoon Kim, George J. Moridis, John Edmiston, Evan S. Um, Ernest Majer. Earth Sciences Division, Lawrence Berkeley National Laboratory 24 Mar.

Transcription

1 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

2 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 2

3 Outlines TOUGH+ROCMECH, T+M o ROCMECH o Coupling to TOUGH+ Shale/tight gas Simulation o Hydraulic Fracturing o Electromagnetic (EM) simulation o Microearthquake(MEQ) Simulation o Failure along the vertical well o Failure during gas production Ongoing Research 3

4 ROCMECH Written in Fortran 95 Employ the finite element method Plasticity Modeling Shear failure, (Mohr-Coulomb model) Tensile failure, (Node splitting method) Plane Strain 2D & Full 3D versions Sequentially coupled to TOUGH family codes (flow simulators) 4

5 RM_Input_3D (_2D) Input Files 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 5

6 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 method Must deal effectively with issues related to accuracy, stability, convergence Fixed-stress sequential method 6

7 TOUGH+ROCMECH (T+M) Space Flow Problem: Finite Volume Method (FVM) Geomechanics: Finite Element Method (FEM) u Mixed formulation P u : displacement at a node P : pressure at a grid center Time Fully implicit time discretization 7

8 Sequential Approach Flow Update porosity, Permeability, Pressure, Saturation, etc. Geomechanics Displacement, Strain, Failure zones, etc Geophysics (MEQ, EM) 8

9 Permeability Coupling Porosity: Fixed-stress split 2 n n 1 n l l l n 1 n n 1 n bl n n 1 l l ( pl pl ) 3 T, l l Tl Tl v v Kl Ks l c Tensile failure: n p Qw ac 12 Shear failure: w k n l k p H ( Gradp wg) w 0 p, f ps, Cubic law, when np=3.0 Higher than shale permeability Stress-pressure-temperature ' σ b pe σ C ε b p 1 3 K e e J J T dr T1, 9

10 Shear Failure f ' m ' m sin Mohr-Coulomb model f c h cos ' m f 0 ' 1 Drucker-Prager model Hydrostatic axis Cohesion ' m ' 3 Mohr-Coulomb model ' 2 Conventional return mapping for shear failure Nonlinearity in geomechanical moduli 10

11 y z Vertical Tensile Fracturing y y x z ' c 2 '2 '2 ' 2 tt ts tn Tc y x z t t t s z Fracture Fracture Node splitting t n t Traction No horizontal displacement Horizontal well Fracture plane By symmetry Fracturing Nonlinearity from the boundary condition Traction boundary Traction boundary 11

12 Code Verification (T+M) 2D Plane strain geomechanics Poromechanical effect Static fractures Fracture propagations Numerical and analytical results are in good agreement. 12

13 Shale/tight gas Simulation o Hydraulic Fracturing o EM simulation o MEQ Simulation o Near-well failure o Failure during gas production 13

14 Fracturing by Water Injection Fracture Main Fracture Closed Open Reservoir gas Small & local fractures Injected Water Stimulated zone 0.0 S w Water saturation Within created fractures, gas & water can coexist. 14

15 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 15

16 y S H z x S V S h 66m Horizontal well 1. Hydraulic Fracturing S w, i 0.1 (Horizontal Well) Fluid Injection 150m 150m Fracture Qinj 17.1MPa 40 kg / s z 23.3MPa 29.1MPa 36.4MPa Sh P G SV SH PG MPa T o C k p E 12.0GPa 0.3 Tc 10.0MPa D Fracture plane Traction boundary Investigate fracture propagation for shale gas reservoirs 16

17 Fracture Propagation 60s 500s Time (s) HW 1200s 1600s HW A fracture grows up and down stably. Fracturing occurs along the fracture tips. 17

18 Water Displacement (I) 60s 500s 1200s 1600s Gas Water Water is only partially saturated within the fracture. 18

19 Water displacement (II) 60s 500s Aperture (cm) Sw Pressure Bottom Top 1200s 1600s Fracture propagation is faster than water movement 19

20 Pressure, Aperture, Displacement Fractured Nodes Pressure (Mpa) Fracture Opening (m) Uplift (m) Saw-tooth (oscillatory) pressure, fracture opening, displacement 20

21 Leak-off of Water Gas Saturation 1600s Damaged Zone Second layer in the y direction Significant leak-off of water might occur. 21

22 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 22

23 Saturation & Electric conductivity 200s 1600s Water saturation Electrical conductivity Nanofluid, σ=1000 S/m, µ r =1 Electrical conductivity (brine: σ=3.3 S/m, µ r =1) 23

24 Vertical Crosswell EM Nanofluid (σ=1000 S/m, µ r =1) Brine (σ=3.3 S/m, µ r =1) 1600s 1200s 500s 200s Source position: z=-1350 m Nanofluids can enhance EM signals significantly. 24

25 Horizontal Crosswell EM Nanofluid (σ=1000 S/m, µ r =1) Brine (σ=3.3 S/m, µ r =1) 1600s 1200s 500s 200s Source position: z=-1440 m Nanofluids can enhance EM signals significantly. 25

26 2. Hydraulic Fracturing (Vertical Well) y S H z x S V Vertical well S h Tc Tc Fracture plane 120m Fluid Injection 10.0MPa 160m 5MPa 600m Fracture Q 90 kg / s inj 300m T 5.0MPa c S S S P k V H h G 54MPa 0.8SV 0.45S V 28MPa p E 10.0GPa Swi D 26

27 Hydraulic Fracturing Injection point Little oscillatory The fracture propagates horizontally and downward due to strong overburden. 27

28 Seismic Moment Tensor M pq m pq d, m v u ( v u v u pq k k pq p q q p ) u ( ux, u y, uz ) M 0 M L 2 displacement v (0,1,0) New fractured area M w log 10 M ( N m )

29 Simulation of MEQ Reasonable Mw Promising to use for reservoir characterization 29

30 3. Vertical Well instability m S h 3D Simulation domain 0.2 S H 5m 0.15 Reservoir 0.1 S V 150m 90m Injection well (cemented) Well casing Cemented area Cement-casing contact 9m Injection well (open) Same previous reservoir conditions Constant Bottom hole pressure,30mpa 30

31 S h Well Failure (Shear Failure along the Well) S H c cm h 10MPa Failure area S V At 1800s Incomplete well cementing causes significant well failure while complete cementing does not c ct h 10MPa Complete cementing c ct h 5 MPa c ct h 1 Incomplete cementing MPa cm c h ct c h : cohesion of cement : cohesion in contact area 31

32 4. Gas production 2D plane strain 20m vertical fracture 10m horizontal fracture Long fractures with horizontal well in 3D 2D plane strain geomechanics (vertical or horizontal fractures) 32

33 Elasticity Prediction ' m ' m sin sin 2 f c f h 1 cos f. Potential Failure Initial Pressure and total stress: 68.5MPa Constant Bottom Hole Pressure: 20MPa E 1.28GPa, 0.22, f 0.5rad, ch 4MPa Weak reservoirs 33

34 Plasticity: Shear Failure 7day 30day 7day 30day Case 1:Vertical Fracture Case 2: Horizontal Fracture 45day 75day 45day 76day Secondary Fracturing & Enhanced Permeability: Enhanced Productivity Dynamic permeability changes flow patterns & geomechanical responses significantly. 34

35 Low effective stress P b B B 20MPa 0.8 Case 1: Vertical Fracture Case 2: Horizontal Fracture P b B B 30MPa 1.0 Significant secondary fracturing might not occur. 35

36 Different Plastic Parameters Case 1: Vertical Fracture Case 2: Horizontal Fracture pb 30MPa Significant secondary fracturing can occur for f 0.35rad Secondary fracturing depends on flow-geomechanics parameters and production scenarios. 36

37 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

38 Parallel Codes Ongoing Research in Geomechaniccs MEQ in various failures Near the stimulated zone, Fault, Strong capillarity Chemo-Thermo-Poro-Mechanics Large deformation (Finite Strain) 38

39 Acknowledgements RPSEA (Research Partnership to Secure Energy for America) EPA (U.S. Environmental Protection Agency) Thank you 39