Coupled hydro-mechanical modelling of dilatancy controlled gas flow and gas induced fracturing in saturated claystone

Abstract

Large quantities of gas can be produced during the lifespan of a deep geological repository (DGR) due to several processes that may affect the integrity of the host rock. Therefore, understanding dilatancy controlled gas flow in saturated claystone is important for assessing the safety of a DGR with argillaceous formations as the potential host rock. In this paper, a coupled hydro-mechanical (HM) model that incorporates double porosity poroelasticity is developed to simulate the gas migration process in saturated claystone. The model accounts for the HM behavior of both the porous medium (which represents the matrix) and the fractured medium (which represents the fractures). Double effective stress principles for each medium are derived from the first law of thermodynamics. The volumetric strains of the matrix and fractures, which are work-conjugated to the respective effective stress level, are explicitly included in the mass balance equations. The developed model is successfully evaluated against three gas injection tests on claystone at the laboratory scale. The main experimental observations, i.e., the development of gas preferential pathways, volume dilation, and gas induced fracturing, are well captured.