Simulation of Microscopic CO ₂ Storage Process in Saline Aquifers Based on Three-Dimensional Pore Network Model

Carbon capture, utilization, and storage (CCUS) technology is important for achieving carbon reduction. Current studies on seepage characteristics during CO2 storage in saline aquifers focus primarily on reservoir-scale and core-scale investigations, with relatively few simulations of microscopic seepage characteristics at the pore scale. To address the above issues, in this paper, four three-dimensional pore network models of actual rock cores are established via computed tomography (CT) scanning technology. Based on microscopic numerical simulation methods coupled with multiple physical fields, the microscopic seepage process of CO2 and water two-phase interfaces is studied to characterize the microscopic seepage characteristics of free gas, adsorbed gas, and dissolved gas. The effects of the injection velocity, wettability angle, and injection concentration on the microscopic seepage characteristics of CO2 displacing water are analyzed. The results indicate that pore structure influences the migration direction of CO2. In Model 1, CO2 preferentially migrates toward the upper and middle pore zones after injection. At the end of displacement, CO2 primarily exists as a continuous phase, whereas water is distributed in localized clusters, blind-ended structures, and blocky formations. The average CO2 concentration increases rapidly in the initial phase and levels off in the middle and late phases. The average CO2 adsorption concentration increases slowly in the initial phase but nearly linearly in the middle and late phases. The average H2CO3 concentration first increases but then decreases. At the same simulation time, increasing the injection velocity and concentration enhances the average CO2 concentration within the pores, the average CO2 adsorption concentration on the pore walls, and the average H2CO3 concentration. When the water wetting angle is 135°, CO2 exhibits stronger sweep capacity. These results are highly important for further understanding the microscopic storage mechanisms of CO2 at the pore scale of saline aquifers at mining sites.