Coupled hydromechanical model for evaluating the volume change and fluid permeation behavior of expansive clay smear in a fault upon interaction with CO<inf>2</inf>

The interaction between clay minerals and CO2 at in-situ conditions of geological carbon sequestration leads to adsorption-induced strain, which increases the mineral's interlayer space. The effect of change in interlayer spacing of minerals on the evolution of macro-permeability, gas storage capacity, gas pore pressure, and stress state of compacted clays is unknown. The present study described a coupled numerical model to investigate the effect of adsorption-induced swelling of smectite-based clay on its gas permeation and mechanical properties upon interaction with CO2. To simulate the interaction of the fill material present in caprock faults with the injected CO2, compacted clay under confined, free and uniaxial confinement conditions are analyzed. It is evident under confined conditions, permeability of the clay filled in fault reduced, and mean compressive stress increased due to gas adsorption-induced strain. On the contrary, the permeability of the clay increased for both free and uniaxial conditions. The magnitude of the swelling stress within the media under uniaxial conditions depends on the degree of expansion caused by the adsorption-induced effect and applied overburden pressure. Overall, the study contributes to a comprehensive approach to evaluate the efficacy of geological formations having faults for long-term storage of CO2 in them.