Direct Numerical Simulation of CO₂─Water Reactive Dissolution in Real Rock: Influence of Capillary Number and Wettability During Drainage Process

A fundamental comprehension of the intricate interactions following CO2 injection into the reservoir is critical in geological carbon sequestration. In this study, we performed pore-scale simulation to couple two-phase flow, multicomponent transport, and geochemical reactions. We investigated the dynamic reactive dissolution during the CO2 injection process, considering the influence of capillary number and wettability. Furthermore, we analyzed the temporal and spatial evolution of multiple chemical components (CO2 (aq), CO32-, HCO3-, and H+) within a complex pore structure. Based on these analyses, we proposed an empirical formula to describe the average pH evolution over time. The pore structure significantly influences the dynamic evolution of the two-phase interface, leading to nonuniform reactive dissolution and pronounced differences in hydrochemical responses across different pores. A rapid decrease in pH creates a moderately to strongly acidic environment, while the distribution of CO32- and dissolved CO2 exhibits notable variability. This can result in mineral dissolution in the inlet region and precipitation at the distal end of the formation. Capillary number and wettability play a crucial role in reactive dissolution by modulating the evolution of the two-phase interface. Under medium capillary number and strongly water-wet conditions, the two-phase interface behavior becomes more active, with reactive dissolution further enhancing interface activity and promoting phenomena such as Haines jumps and snap-offs.