Hydromechanical processes of supercritical CO₂intrusion into shaly caprocks

It is widely accepted that massive deployment of Carbon Capture and Storage (CCS) in geologic media at the gigatonne scale should be part of the mitigating pathways toward net-zero CO2 emissions. For a successful geologic CO2 storage, the caprock sealing capacity and the associated governing processes have to be assessed in detail. In this contribution, we aim at improving our understanding of hydromechanical processes induced by dynamics of CO2 leakage through intact shaly caprocks. To this end, we perform laboratory experiments on supercritical CO2 injection into a caprock sample under representative subsurface conditions. We numerically simulate the process to provide a mechanistic interpretation of experimental observations. Overall, we find that CO2 intrusion into the pore network increases pore pressure and triggers hydromechanical coupling effects, mainly causing the specimen to expand after an initial transient compaction. The pressure-induced rock expansion slightly enhances the porosity and permeability, promoting CO2 flow close to the upstream. However, the high entry pressure and ultra-low effective permeability of the non-wetting phase limit the bulk volumetric penetration of CO2 deep into the caprock. Therefore, advective flow of CO2 is restricted to the lowermost portion of intact caprock, whereas diffusion extends along the whole caprock sample.