Pore-scale investigation of three-phase immiscible and miscible displacement in a realistic three-dimensional porous medium

Geological CO₂ storage serves as a critical approach for mitigating global warming and enhancing oil recovery, which frequently involves three-phase (oil-water-CO₂) displacement processes in porous media. Under the authentic high-temperature and high-pressure conditions of actual reservoirs, CO₂ often achieves miscibility with crude oil. This study employs a three-phase three-dimensional lattice Boltzmann method to simulate the miscible displacement process in a porous medium where oil and CO₂ achieve miscibility while water remains immiscible. The model is verified through Janus droplet simulations and Fick's law simulations. Using the above method, three-phase dynamic behaviors and displacement processes are studied under both miscible and immiscible conditions with varying wettability, capillary numbers, and diffusion coefficients. The pore-scale results indicate that miscible conditions significantly improve both oil recovery and gas storage efficiency compared to immiscible scenarios. Increased diffusion coefficients and reduced capillary numbers enhance miscible oil recovery and CO₂ storage capacity. While water-wet conditions improve oil recovery, they conversely inhibit gas storage efficiency.