Abstract
A thorough understanding of the microscopic flow process in porous and fractured media is significant for oil and gas development, geothermal energy extraction and subsurface CO 2 storage etc. In CO 2 geological sequestration, the CO 2 is often injected at the supercritical state (scCO 2 ), which will displace the connate fluids in the pore spaces during the drainage process. However, when CO 2 injection stops, the connate brine or water flows back to displace the scCO 2 . Therefore, the configuration of migration paths in a specific reservoir plays a significant role in affecting the connectivity and storage efficiency of scCO 2 . In this paper, the two-phase (scCO 2 and water) boundary has been defined using the phase field method, and the COMSOL Multiphysics simulator is applied to study the migration of scCO 2 in porous/fractured media at the pore scale. The geological conditions of Shiqianfeng formation in the CO 2 capture and storage pilot site of the Ordos Basin in China is selected as the engineering background. Before using the actual microscopic geometry based on thin-section of Shiqianfeng sandstone, we get the general understanding on scCO 2 migration in fractured porous media that has the highly simplified configuration with circular particles, considering the impacts of wettability, geometry of formation mineral grains, interfacial tension, injection rates, and fracture geometry. Results show that the CO 2 preferential flow occurs at locations with high CO 2 flow rates and high CO 2 pore pressure. The preferential flow of scCO 2 occurs adjacent to the wall of grains while minimal or little flow takes place through the interior between the grains, considering the grains with irregular shapes. The interfacial tension of porous media plays a significant role in controlling the spatial distribution of the scCO 2 . A much lower interfacial tension results in a much thinner scCO 2 flow band with a much higher saturation. The geometry of fractures in porous media increases the complexity of the scCO 2 flow paths at the pore scale. Cited as : Liu, H., Zhu, Z., Patrick, W., Liu, J., Lei, H., Zhang, L. Pore-scale numerical simulation of supercritical CO 2 migration in porous and fractured media saturated with water. Advances in Geo-Energy Research, 2020, 4(4): 419-434, doi: 10.46690/ager.2020.04.07
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