Pore scale modeling of wettability impact on CO2 capillary and dissolution trapping in natural porous media

Understanding CO₂ capillary trapping and dissolution trapping behaviors in deep saline aquifers is essential for improvement of sequestration efficiency. This study investigated the impact of rock wettability on CO₂ capillary and dissolution trapping in a Ketton carbonate rock through direct numerical simulation. Based on experimentally measured CO₂-brine-rock physics data, we performed the pore-scale simulation of drainage process under four wettability conditions, followed by imbibition process under six sets of flow rate conditions. The dynamic evolution of CO₂ clusters and dissolved CO₂ distribution during drainage and imbibition processes was tracked simultaneously. Our results showed that wettability significantly influenced the morphology of trapped CO₂ clusters, consequently impacting the dissolution behavior. During drainage process, CO₂ saturation is higher in relatively hydrophobic rock but the dissolution capacity is lower because of the lower specific interfacial area. During imbibition process, the trapped scCO₂ saturation is also higher in relatively hydrophobic rock, and the number of CO₂ clusters is higher with more dispersed distribution. Increasing the flow rate can significantly reduce the residual CO₂ saturation and thus affect the dissolution efficiency. The function relationship between Sherwood number Sh calculated by mass transfer coefficient $\bar{k}$ and flow rate-dependent Péclet number Pe under different wettability conditions was proposed. The CO₂ dissolution process is more affected by the flow rate under relative hydrophilic conditions.