Pore-scale numerical simulation of CO2-water alternating gas injection for enhanced oil recovery in heterogeneous porous media

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To address the problem of low oil recovery efficiency during CO 2 flooding in low-permeability and heterogeneous reservoirs, a two-dimensional microscale numerical model for the three-phase flow of oil, gas, and water is developed. The model simulates immiscible three-phase flow of oil, gas, and water during the CO 2 -Water Alternating Gas (WAG) injection process, with a particular focus on the effects of heterogeneous pore structures on displacement mechanisms. The model incorporates continuous surface force and adhesion force terms, as well as gravity, to enhance its capability in capturing interfacial evolution and wettability effects in three-phase systems. Under varying conditions of heterogeneity and crude oil viscosity, the impacts of three key parameters—water-gas ratio, injection rate and slug size—on microscale displacement characteristics are systematically investigated. The results indicate that gravity has a non-negligible influence throughout the displacement process. Moreover, the injection parameters play a significant role in determining displacement performance. Proper optimization of these parameters can effectively enhance sweep efficiency and oil recovery during CO 2 -WAG injection.