Flow-coupled-geomechanical modelling of CO2 transport in depleted shale from a microscopic perspective

Abstract

Depleted shale reservoirs are the potential candidate sites for long-term geologic storage of CO2. However, understanding of CO2 transport behavior in shale is still a challenge because of the heterogeneity of shale matrix. In this paper, a flow-coupled-geomechanical model is developed for analyzing CO2 transport at the microscale. This model is able to simultaneously capture the geomechanical deformation of organic matter (OM) and inorganic matter (iOM), gas transport in OM and iOM, gas sorption in OM, and both solid and fluid interactions between OM and iOM. The obtained results show that due to shale matrix heterogeneity, i.e., coexistence of OM and iOM, CO2 transport and shale matrix deformation behaviors exhibit regional differences. Specifically, during CO2 injection, pore pressure in OM increases slower, Knudsen number in OM has larger value, apparent permeability in OM is smaller, and volumetric strain in OM is larger. Thus, taking matrix heterogeneity into account is necessary. Moreover, sensitivity analysis indicates that during CO2 injection the apparent permeability of OM changes with both OM and iOM properties while the apparent permeability of iOM only changes with iOM properties. The flow-coupled-geomechanical modelling provides new insights for understanding CO2 transport in depleted shale from a microscopic perspective.