Simulation of the Microscopic Seepage Process of CO2 Storage in Saline Aquifers at the Pore Scale

CO2 storage in saline aquifers is an important measure for CO2 capture and storage (CCS), which can effectively reduce greenhouse gases. Current studies on CO2 storage in saline aquifers mainly focus on the storage mechanism, fluid migration process, reservoir pressure evolution, and injection feasibility, but the models used in the studies are mostly macroscopic models, and it is difficult to accurately describe the microscopic seepage process of CO2 in the pore space. To address the above research problems, this paper adopts a finely processed two-dimensional model of the core pore structure based on numerical simulation methods to simulate the microscopic seepage process of the CO2 storage process in saline aquifers at the pore scale. The research results show that during the displacement process, CO2 injection breaks through rapidly along the main flow line while seeping upward under the effect of the oil-water density difference and advancing forward in an irregular slope, causing the gas saturation to increase continuously. In the suction process, under the action of gravity, saline water is transported forward along the slope. After CO2 injection, it will preferentially diffuse into the large pore saline water. The chemical products are mainly located in the diffusion and dissolution zones of CO2 in water. The increase in the injection velocity during the displacement process will reduce the gas breakthrough time at the outlet. During the suction process, the increase in the injection velocity is beneficial to accelerate the water displacement process and will result in a reduction in the residual gas storage rate. The increase in the water contact angle will result in a decrease in the suction process time and an increase in the residual gas storage rate. This study has important implications for understanding the CO2 plume migration laws and the CO2 storage mechanisms from a microscopic perspective at the mine.