Experimental Study on the Enhancing Oil Recovery Mechanisms and Displacement Law of CO₂ High Speed Flooding in Low Permeability Reservoirs

In order to clarify the production mechanism and development effect of CO₂ pressure flooding in heavy oil reservoir, this study analyzed the action mechanism of CO₂ on heavy oil by using phase simulation technology. Based on the finite element discrete method, a coupling model of seepage field and stress field was established to analyze the influence of injection pressure on fracture propagation behavior. Based on the simulation results of fracture generation, a numerical model considering the formation of complex fractures after CO₂ composite pressure flooding was established for the simulation of reservoir production after pressure flooding. A numerical simulation method of CO₂ pressure flooding for heavy oil reservoirs based on reservoir dynamic parameters was developed. The propagation behavior of fractures during CO₂ pressure flooding was studied, and the technological parameters of CO₂ pressure flooding were optimized. The simulation results show that the main mechanisms of CO₂ flooding include reducing oil viscosity, expanding oil, enhancing oil fluidity, creating fractures near injection Wells to improve CO₂ injection capacity and increasing formation pressure. The CO₂ pressure flooding results of heavy oil show that CO₂ has a good energy increasing effect, and CO₂ migration is seriously affected by the heterogeneity of the reservoir. The gas overburden leads to the accumulation of CO₂ in the upper part of the reservoir, and the viscosity reduction effect of the upper part of the oil is more significant. Through the optimization of CO₂ pressure flooding process parameters for heavy oil, it is suggested that the pressure flooding injection pressure should be controlled within 40～50 MPa. The results of this study have certain guiding significance for the design and field application of CO₂ pressure flooding in heavy oil reservoirs.