Field-scale investigations on long-term dynamic wettability alteration in underground CO2 storage

The wettability of the CO2/fluid/rock systems plays a crucial role in plume migration and storage efficiency in underground CO2 storage. While wettability is typically considered a static property, recent studies indicate that contact angles can change over time due to prolonged exposure to the injected CO2. This time-dependent wettability alteration process and the associated impact on the performance of underground CO2 storage have not been reported before. In this study, a time-dependent transition from a strongly water-wet state to a weakly water-wet state is considered. The corresponding dynamic changes in macroscopic properties, including relative permeability, capillary pressure, and hysteresis, are implemented in field-scale simulations of CO2 storage in saline aquifers. We analyzed the impact of the wettability alteration process on the CO2 plume migration, local CO2 dynamics, wettability transition status, residual trapping, and dissolution trapping. The results indicate that a wettability alteration process leads to a more extensive plume extent in underground CO2 storage, thereby enhancing dissolution trapping. However, it can result in an initial increase followed by a decrease in residual trapping due to the release of previously trapped CO2. For instance, if wettability alteration occurs upon a 2000-day CO2 exposure (i.e., the system turns weakly water-wet), plume extent increases by 18 %, dissolution trapping by 5.2 %, whereas residual trapping decreases by 49.7 %. Overall, the wettability alteration systems exhibit performance comparable to the final static wetting state as long as the wettability transition is fully completed. The results of this study thus highlight the importance of incorporating dynamic wettability evolution into reservoir characterization frameworks to assist with site selection and long-term risk assessments for CO2 geological storage.