Mechanism and Law of CO₂ Pressure Flooding in Enhancing Oil Recovery in Low-Permeability Heavy Oil Reservoirs

In order to clarify the production mechanism and development effect of CO₂ pressure flooding in low-permeability heavy oil reservoirs, the influencing mechanisms of CO₂ on heavy oil were analyzed by using phase simulation technology. Based on the finite element discrete method, the coupling model of the seepage field and stress field of fracture propagation was established, and the influence of injection pressure on fracture propagation behavior was analyzed. According to the simulation results of fracture generation, a numerical model considering the formation of complex fractures after CO₂ combined pressure flooding was established, and the reservoir production after pressure flooding was simulated. A numerical simulation method of CO₂ pressure flooding for heavy oil reservoirs was developed based on dynamic reservoir parameters. The law of fracture propagation during CO₂ pressure flooding was analyzed, and the technological parameters of CO₂ pressure flooding were optimized. The simulation results show that the main influencing mechanisms of CO₂ pressure flooding include reducing crude oil viscosity, expanding crude oil, enhancing crude oil fluidity, fracturing near injection wells to improve CO₂ injection capacity, and increasing formation pressure. CO₂ has a good energy enhancement effect, and CO₂ migration is greatly affected by the heterogeneity of the reservoir. Gas overlap leads to the accumulation of injected CO₂ in the upper part of the reservoir, and the crude oil viscosity reduction effect in the upper part of the reservoir is more significant. By optimizing the technological parameters of CO₂ pressure flooding for heavy oil, it is suggested that the injection pressure of pressure flooding should be controlled at 40–50 MPa. The research results can guide the design and field application of CO₂ pressure flooding in heavy oil reservoirs.