1. Lawrence Livermore National Laboratory Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 Direct Numerical Simulation of Fluid Driven Fracturing Events with Application to Carbon Sequestration Joseph Morris and Scott Johnson LLNL-PRES-404894

2. 2 Lawrence Livermore National Laboratory Geomechanical response represents a primary source of risk to successful CO 2 storage Low permeability caprock E.g: Shale  Injection of enormous volumes of CO 2 will cause Increased pore pressures Large scale reservoir deformation  These mechanisms alter stresses in Caprocks Pre-existing fractures and faults High porosity/ permeability reservoir E.g: Saline aquifer

3. 3 Lawrence Livermore National Laboratory  Need to establish what CO 2 pressures will lead to risk of caprock failure under reservoir conditions Caprock seal failure mechanisms  We are investigating three sources of risk: Creation of new fractures Activation of faults Activation of fracture networks

4. 4 Lawrence Livermore National Laboratory Livermore Distinct Element Code (LDEC): Key Features and Capabilities  Fully 3-D fully coupled fluid-solid solver  Distinct Element Method (DEM) Module Rock mass represented by arbitrarily shaped polyhedral blocks  Can accommodate realistic joint-sets Empirical joint models – slip, hysteresis, dilation Block representations:  Rigid / Uniform deformation (“Cosserat blocks”) / Finite elements All block types support:  Dynamic contact detection  Dynamic fracture/fragmentation  Smooth Particle Hydrodynamics (SPH) Module Fully coupled fluid dynamics  Flow network solver Fully coupled fluid dynamics confined within fractures  Fully parallelized: Demonstrated on up to 8000 CPUs  Will be available under license from LLNL shortly

5. 5 Lawrence Livermore National Laboratory  Need to establish what CO 2 pressures will lead to risk of caprock failure under reservoir conditions Caprock seal failure mechanisms  We are investigating three sources of risk: Creation of new fractures Activation of faults Activation of fracture networks

6. 6 Lawrence Livermore National Laboratory Dynamic Fracture: Experiment with a notched plate  It is observed that as loading rate is increased, crack velocity is limited and falls short of the Rayleigh wavespeed [From Zhou, F., Molinari, J.-F., and T. Shioya, 2005]

7. 7 Lawrence Livermore National Laboratory Dynamic Fracture: Cohesive Elements  Nodes split when specified fracture criteria are met Tensile Shear  Introduce cohesive element between new nodes: Ensures correct energy is dissipated (proportional to surface created) Reduces mesh size dependence  Currently fracture must follow existing element boundaries

8. 8 Lawrence Livermore National Laboratory Dynamic Fracture: LDEC Cohesive Elements Block, Rubin, Morris and Berryman (2008)

9. 9 Lawrence Livermore National Laboratory We have recently added a network flow capability to support simulation of hydraulic fracture LDEC:  Add coupling with matrix geomechanical response  Triangular finite volumes with element-centered pressure  Fully coupled with solid elements to model hydrofracture Koudina et. al. (1998):  Flow through fractures on an unstructured mesh  Lacks coupled geomechanics  Triangular finite volumes with node-centered pressure

10. 10 Lawrence Livermore National Laboratory LDEC Demonstration of hydraulic fracture  Pressurized crack propagates into the rock  Prediction of caprock and reservoir rock integrity  Characterization of seismic sources for far-field detection and interpretation y: 4 cm x: 6 cm z: 6 cm Initial fracture

11. 11 Lawrence Livermore National Laboratory  Need to establish what CO 2 pressures will lead to risk of caprock failure under reservoir conditions Caprock seal failure mechanisms  We are investigating three sources of risk: Creation of new fractures Activation of faults Activation of fracture networks

12. 12 Lawrence Livermore National Laboratory Simulation of fault activation due to fluid injection: Application to Teapot Dome  Change in pore pressure that will result in activation of given location on S1 fault (similar to Chiaramonte et al, 2007).  Plot of fault area activated as a function of increase in pore pressure on fault surface Facets of fault considered in isolation Full geomechanics with LDEC

13. 13 Lawrence Livermore National Laboratory  Need to establish what CO 2 pressures will lead to risk of caprock failure under reservoir conditions Caprock seal failure mechanisms  We are investigating three sources of risk: Creation of new fractures Activation of faults Activation of fracture networks  Caprock/reservoir

14. 14 Lawrence Livermore National Laboratory Simulation of injection into a heavily fractured reservoir Fracture network Delta-Pore pressure field  Small test problem: 13 thousand, variably oriented fractures  Anisotropic stress field:  east =  overburden,  north = 0.6  overburden  Distinct element model with explicit fracture elements modeled between arbitrary polyhedral blocks

15. 15 Lawrence Livermore National Laboratory Simulation of injection into a heavily fractured reservoir  The proportion of joints of each orientation relative to North that have failed during fluid injection  Joints of all orientations fail due to redistribution of stress Predominantly those initially experiencing shear stress  Provide predictions of permeability change  Predict energy release from fractures during injection

16. 16 Lawrence Livermore National Laboratory Conclusions  Caprock integrity represents a significant potential source of risk to successful geologic storage of CO 2  LDEC has demonstrated capabilities for predicting: Fluid driven fracturing events Activation of existing faults Activation of existing networks of fractures  Moving forward: Parameter studies to evaluate risk to CO 2 containment Funded to participate in large scale field projects  Other applications: Unconventional gas/oil recovery

17. 17 Lawrence Livermore National Laboratory Extras…  Extras…

18. 18 Lawrence Livermore National Laboratory We are developing interfaces between LDEC and FRAC-HMC to span the scales of interest O(1 km) O(1 m) O(10 m) Local fracture network scale: Simulation of consequent fracture network permeability and local stress change  FRAC-HMC/LDEC Individual Fracture scale: Simulation of activation and creation of caprock fractures  LDEC Reservoir Scale: Simulation/Measurement of insitu conditions during operation  NUFT, partners in industry

19. 19 Lawrence Livermore National Laboratory Simulation of fault activation due to fluid injection 5 km 2 km reservoir Fault plane 5 km well  Finite element model with fault modeled by material with shear strength dictated by prescribed coefficient of friction

20. 20 Lawrence Livermore National Laboratory Simulation of fault activation due to fluid injection Mounding due to injection  Slip on fault results in discontinuity in surface expression Slip on fault results in reduced displacement on other side of fault Injection source at 1500m depth