CO₂-EOR microscopic mechanism under injection–production coupling technology in low-permeability reservoirs

Injection–production coupling (IPC) technology holds substantial potential for boosting oil recovery and enhancing economic efficiency. Despite this potential, discussion on gas injection coupling, especially in relation to microscopic mechanisms, remains relatively sparse. This study utilizes microscopic visualization experiments to investigate the mechanisms of residual oil mobilization under various IPC scenarios, complemented by mechanical analysis at different stages. The research quantitatively assesses the degree of microscopic oil recovery and the distribution of residual oil across different injection–production methods. Findings reveal that during the initial phase of continuous gas injection (CGI), the process closely mimics miscible displacement, gradually transitioning to immiscible displacement as CO₂ extraction progresses. Compared to CGI, the asynchronous injection–production (AIP) method improved the microscopic oil recovery rate by 6.58%. This enhancement is mainly attributed to significant variations in the pressure field in the AIP method, which facilitate the mobilization of columnar and porous residual oil. Furthermore, the synchronous cycle injection (SCI) method increased microscopic oil recovery by 13.77% and 7.19% compared to CGI and AIP, respectively. In the SCI method, membrane oil displays filamentary and Kármán vortex street flow patterns. The dissolved and expanded crude oil tends to accumulate and grow at the oil–solid interface due to adhesive forces, thereby reducing migration resistance. The study findings provide a theoretical foundation for improving oil recovery in low-permeability reservoirs.