Volume 57

Pore-Scale Investigation of Oil Displacement Mechanisms in Low-Salinity Carbonated Water Flooding Rongjiang Liu,Shuyang Liu, Li Wang, Junrong Liu, Baojiang Sun

Abstract

Low salinity carbonated water flooding (LSCWF) combines the advantages of low salinity water flooding (LSWF) and carbonated water flooding (CWF). It is considered as one of the most promising CO₂-Enhanced Oil Recovery (CO₂-EOR) methods with effectively achieving carbon sequestration. However, the mechanism of LSCWF enhancing oil recovery at the pore scale remains unclear, which hinders the development and application of this technology.To bridge the gaps, this work developed a mathematical model that couples the Navier-Stokes equation, the phase field method equation, and the convection-diffusion equation to study the microscopic mechanism of low salinity carbonated water displacing oil. The dynamic distribution patterns of oil and water of LSCWF in the porous media were analyzed and compared with water flooding (WF) and LSWF. The microscopic oil recovery enhancement mechanism of low salinity carbonated water in different types of channels is emphatically analyzed, and a parameter sensitivity analysis is carried out.The results show that when the recovery factor of LSCWF reaches 81.83% after 10 PV displacement, which is significantly better than that of water flooding (61.57%) and low salinity water flooding (67.02%). Microscopic analysis reveals that this is mainly attributed to the remarkable increase in the recovery of blind ends, main channels, and cluster regions by low salinity carbonated water. The key microscopic mechanisms involve the mass transfer of CO₂ from carbonated water into the oil phase, which reduces oil viscosity at the fluid interface, improves the oil-water mobility ratio, and significantly enhances water-phase scouring efficiency. And LSCWF can also significantly decrease the seepage resistance, and strip out more residual oil. This study reveals the pore scale microscopic mechanism of LSCWF for EOR, supporting efficient complex reservoir development and the “dual carbon” goal.

Keywords CCUS,CO2-EOR,low-salinity carbonated water flooding,pore-scale,numerical simulation