Coupling of STOMP and ABAQUS for Hydro-Geomechanical Modeling of Fluid Flow and Rock Deformation Associated with Subsurface CO2 Injection

Geomechanical alteration of porous media is generally ignored for most shallow subsurface applications, whereas CO2 injection, migration, and trapping in deep saline aquifers will be controlled by coupled multifluid flow, energy transfer, geomechanical, and geochemical processes. The accurate assessment of the risks associated with potential leakage of injected CO2 and the design of effective injection systems requires that we represent these coupled processes within numerical simulators. The objective of this study was to examine the coupling of hydraulic and geomechanical processes for simulation of CO2 injection into the subsurface for carbon sequestration. The impact of nonisothermal multifluid flow and porous media deformation mechanics on CO2 migration and storage was evaluated. We present a sequentially coupled approach for multifluid and geomechanical simulation using STOMP and ABAQUS that has been developed and validated through comparison to the solutions for benchmark problems that were solved with a coupled TOUGH-FLAC simulator. The poroelastic model was implemented with user-subroutines in ABAQUS. We also compare the STOMP-ABAQUS simulator to a new version of STOMP that includes the fully coupled poroelastic simulation within the multifluid flow and transport simulator. The poroelastic model computes stiffness, stresses, and strains using aqueous and gas pressures as well as saturations from STOMP output, and provides STOMP with the updated permeability, porosity, and capillary pressure over time during the simulation. The hydraulic only (uncoupled from mechanics) simulation and the hydrogeomechanical (coupled) simulation results using STOMP-ABAQUS were comparable to the previous results of a TOUGH-FLAC simulator. Results from the STOMP-ABAQUS coupled simulator were essentially identical to the fully coupled STOMP hydrogeomechanical simulator when the sequential coupling occurred at small time steps, and deviations between results increased with increasing coupling time steps, especially near the beginning of the injection period. The permeability and porosity increase upon CO2 injection due to porous media deformation, which decreases pore pressures and increases CO2 storage in the formation. A transient delay in CO2 permeability increases was observed due to both the relative permeability changes with increasing CO2 saturation and the propagation of deformation away from the injection location. These results illustrate some of the intricacies and impacts associated with the intimately coupled nature of geomechanics and hydraulics associated with CO2 sequestration systems.