PNNL

Abstract

We present a hydro-mechanical model that couples the fluid flow, geomechanical deformation, and fracturing processes together to enhance the sustainability analysis for geological sequestration of CO2. The fluid flow, geomechanical deformation, and fracturing due to the injection of fluid are all modeled by the bonded discrete element method (bonded-DEM), where fluid flow is modeled by solving the Darcy flow directly on the Lagrangian particles. Because of the high computational expense of the bonded-DEM, the bonded-DEM is only used in the domain where fracturing is highly possible, namely the area near to the injection well and around the pre-existing fault. For the area far away from the high risky domain, the deformation and pressure solutions are obtained by a standard finite element method (FEM). The stress, deformation, and pressure obtained from FEM are fed back into the bonded-DEM simulations as the boundary conditions that were applied to the DEM boundary particles. The DEM simulation results were first compared and validated with a FEM simulation for a case where no fracturing is allowed. For fracturing simulations, the fracture growth speed estimated by this model was also compared with an analytical analysis. The proposed model can be used to evaluate the safety and sustainability of a sequestration site. By predicting the critical time when the fault is reactivated and the time when CO2 breaks through the caprock through the reactivated fault. The model also shows that the ground surface displacement can be used as an effective indicator for fracturing, fault reactivation, and CO2 breakthrough in aquifer and caprock. This can be a very useful monitoring method for the safety of any sequestration site.