Enhancing Oil Recovery in Tight Oil Reservoirs through CO ₂ –C ₂ H ₆ –DME Injection: Experimental and Molecular Dynamics Simulation

CO2 flooding technology is commonly used in the oil and gas field development industry for oil recovery. However, injecting CO2 to improve oil recovery also faces the challenges of viscous fingering at the front edge of displacement and poor overall sweep efficiency. This study employs molecular dynamics simulation to investigate the occurrence, swelling factor, and changes in minimum miscible pressure among various gases (CO2, CO2–C2H6, and CO2–C2H6–DME) and crude oil molecules in a bulk form. At the same time, micro visualization experiments and core displacement experiments were used to study the recovery rate changes of different injected gases. The research findings suggest that the inclusion of C2H6–DME enhances the extraction of high-carbon substances in crude oil by CO2 compared to that of pure CO2. This addition facilitates the extraction of C3–C4–C6–C10 molecules from multicomponent crude oil into the gas phase, resulting in a 50% increase in the crude oil expansion coefficient and a 2.26 MPa reduction in minimum miscible pressure, thereby improving mixing efficiency. After pure CO2 displacement, the remaining oil is mainly distributed in clusters (58%) in the pores of the chip. After composite gas displacement, the remaining oil in the chip is mainly distributed in the film and column shapes.