Coupled hydromechanical controls on CO2 leakage through fractured caprocks

Permanent containment of injected CO2 remains central to the effectiveness and safety of geologic carbon storage. Yet, uncertainties in coupled hydromechanical and multiphase processes limit assessment of leakage through fractured caprocks. Here, we integrate laboratory measurements of two-phase and hydromechanical properties of fractured shales into field-scale simulations to improve evaluation of CO2 leakage potential. Regardless of the caprock sealing capacity, CO2 migration remains strongly localized along fractures, while its rate and extent are governed by non-local interactions with surrounding formations. Despite fracture breakthrough, CO2 discharge into the overlying aquifer is limited. The high-permeability aquifer promotes rapid pressure dissipation and CO2 dissolution, restricting formation of a secondary mobile plume. We conclude that reliable assessment of CO2 leakage likelihood and severity hinges on system-scale resolution of coupled hydromechanical processes. The developed framework will enable reliable integration of advances in experimental fracture characterization into site-specific modeling efforts and, where necessary, remediation design.