Research on the Microscopic Migration Law of CO2 in Salt Water Storage Based on Pressure Driving

CO2 capture, utilization, and storage (CCUS) is a beneficial measure for controlling carbon emissions and reducing greenhouse gases. At present, most of the studies on CO2 storage describe the mechanism, calculation of storage volume, calculation of cap breakthrough pressure and CO2 migration law at the macroscopic level, but there are few studies on the CO2 transport law in the storage process at the microscopic pore scale. This paper establishes numerical formulas for CO2 migration and interface characterization at the pore scale based on numerical simulation methods. Using a two-dimensional model of porous media, a pressure-driven approach is used to simulate the microscopic migration characteristics of CO2 during the storage process of salt water layers. The CO2 migration law is explained, and the influence of pressure and wettability on the migration law is analyzed. Research has shown that during the injection process, CO2 will migrate along the mainstream toward the outlet. Meanwhile, due to the density difference between the two phases, CO2 will migrate upward until it reaches the top of the model. At the end of injection, residual water is mainly distributed at the edges and corners of the model. During the suction process, residual CO2 gas will be trapped at the top and upper right corner of the model under hydraulic and boundary effects. The increase in injection pressure will reduce the full displacement time and increase the residual gas burial rate. The weakening of wall hydrophilicity will shorten the displacement process time, increase the suction process time, and gradually reduce the maximum burial rate. This study characterizes the flow pattern of two phases during CO2 storage in the salt water layer from a microscopic perspective, which has reference significance for further understanding the CO2 storage mechanism in mines.