Mudrock wettability at pressure and temperature conditions for CO2 geological storage

Structural trapping provided by seals is one of the key components of CO₂ geological storage systems. Clay-rich caprocks and fault gouge are expected to be water-wet at supercritical CO₂ conditions and to create a positive capillary pressure $P_{C{O}_2}-P_w>0$MPa to ensure trapping of buoyant CO₂. This paper presents the results of water imbibition experiments in resedimented clay mudrocks immersed in supercritical CO₂ at temperature T ≥ 60 °C and pressure $P_{C{O}_2}$ ≥ 25 MPa. The samples used in this work include kaolinite clay and Anahuac shale from the Gulf of Mexico Coast. Additional validation tests include Berea sandstone and silane-treated Berea sandstone. The results show spontaneous and rapid imbibition of water droplets into resedimented and rock samples initially saturated with wet supercritical CO₂ for all cases. This outcome provides indirect evidence that typical siliciclastic caprock building minerals remain water-wet to CO₂ at typical storage pressure and temperature conditions. The results and analysis indicate that siliciclastic caprock and fault gouge are expected to develop a positive capillary entry and breakthrough pressure to hold buoyant CO₂ by capillary forces. These results validate expectations of buoyant CO₂ structural trapping and field observations from natural analogues.