Numerical visualization of supercritical CO2 displacement in pore-scale porous and fractured media saturated with water

• Main Authors: Hejuan Liu, Zhengwen Zhu, Were Patrick, Jianfeng Liu, Hongwu Lei, Liwei Zhang
• Format: Article
• Language: English
• Published: Yandy Scientific Press 2020-12-01
• Series: Advances in Geo-Energy Research
• Subjects: two-phase flow; phase field method; displacement; preferential flow; fractured media
• Online Access: https://www.yandy-ager.com/index.php/ager/article/view/284

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 CO2 storage etc. In CO2 geological sequestration, the CO2 is often injected at the supercritical state (scCO2 ), which will displace the connate fluids in the pore spaces during the drainage process. However, when CO2 injection stops, the connate brine or water flows back to displace the scCO2 . Therefore, the configuration of migration paths in a specific reservoir plays a significant role in affecting the connectivity and storage efficiency of scCO2 . In this paper, the two-phase (scCO2 and water) boundary has been defined using the phase field method, and the COMSOL Multiphysics simulator is applied to study the migration of scCO2 in porous/fractured media at the pore scale. The geological conditions of Shiqianfeng formation in the CO2 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 scCO2 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 CO2 preferential flow occurs at locations with high CO2 flow rates and high CO2 pore pressure. The preferential flow of scCO2 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 scCO2 . A much lower interfacial tension results in a much thinner scCO2 flow band with a much higher saturation. The geometry of fractures in porous media increases the complexity of the scCO2 flow paths at the pore scale.