Wetting and injecting effects on CO2 distribution: Pore-scale micromodel and simulation

The distribution of CO2 is critical to the efficiency and stability of carbon storage; however, the roles of wettability and capillary number in controlling CO2 distribution remain inadequately understood. In this study, visual waterflooding experiments and numerical simulations were performed using five homogeneous micromodels with distinct wettability characteristics to examine how wettability and capillary number influence CO2 distribution during short-term waterflooding. The results demonstrate that both wettability and capillary number govern CO2 distribution patterns and saturation. These patterns include continuous distribution, cluster-like distribution, and isolated bubbles. Both experimental and simulation data reveal that the total residual CO2 saturation follows a non-monotonic trend with increasing contact angle, while it increases as the capillary number decreases. As the capillary number varies, the displacement behavior transitions gradually from a stable displacement regime to a capillary fingering regime, resulting in variations in residual CO2 saturation. With changing wettability, cooperative pore filling leads to fluid bypassing, thereby modifying the saturation of continuously distributed CO2. In contrast, variations in the saturation of cluster-like and isolated bubble CO2 are attributed to snapoff mechanisms initiated by preceding film flow. This study elucidates how wettability and capillary number govern the residual trapping and distribution of CO2 at the pore scale.