Numerical Simulation Study on CO2 Flooding in Microscopic Heterogeneous Porous Media

Abstract

It is crucial to further investigate the microscopic flow mechanism associated with CO2 miscible and immiscible flooding, reveal microscopic displacement characteristics with different heterogeneities, and determine the feasibility and effectiveness of CO2 flooding. The phase field model is utilized to evaluate the synergistic effects among CO2 injection velocity, oil viscosity, and CO2–oil interfacial tension under different miscibility and reservoir heterogeneity conditions after water flooding. The strong heterogeneous and weak heterogeneous models are constructed to analyze the effect of the various influence factors and determine the microscopic interaction mechanism. The simulation results indicate that CO2 flooding can significantly improve the oil displacement efficiency under heavy oil conditions, and the increment is the greatest. The incremental oil displacement efficiency at heavy oil under miscible and immiscible flooding is 32.19% and 27.97%, respectively. The incremental difference in the oil displacement efficiency between the weak heterogeneous model and the strong heterogeneous model is 4.76% in the immiscible flooding is lower than that of 9.09% in the miscible flooding. This proves that heterogeneity can weaken the effect of miscibility on the oil displacement efficiency. Moreover, the simulation results also prove that the low injection velocity is suitable for miscible flooding in the weak and strong heterogeneous models, and the medium injection velocity is suitable for immiscible flooding in the weak and strong heterogeneous models. For immiscible flooding, CO2–oil interfacial tension is also examined, and it reveals that CO2 flooding is more efficient at lower interfacial tension. These findings can give theoretical insights into laboratory studies and field applications of CO2 flooding.