Oil-CO2 phase behavior in nanoporous media: A lattice Boltzmann study

The complex phase behaviors of oil-CO₂ immiscible diffusion and oil swelling in shale nanoscale space under the influence of competitive adsorption caused by fluid-solid interaction force are still unclear, which is significantly important for shale oil recovery and carbon sequestration. In this paper, a multi-relaxation-time lattice Boltzmann method integrating the two-phase two-component three-distribution Shan-Chen flow model and mass transfer model is established to simulate the CO₂ diffusion through immiscible phase interfaces, oil-dissolved CO₂ competitive adsorption on the mineral surfaces, and oil swelling in nanoporous media. The proposed model is verified by the microfluidic experiment to successfully capture the diffusion and swelling. Then, the effects of equilibrium dissolution concentration and competitive adsorption on CO₂ diffusion/dissolution and oil swelling are studied. The results show that as the equilibrium dissolution concentration increases, the dissolution rate of CO₂ is accelerated, resulting in the increase of oil swelling volume and the dissolved CO₂ adsorption concentration. The mass of CO₂ diffusing into the oil phase increases with CO₂ adsorption capacity, but the oil swelling volume decreases because of the increased CO₂ adsorption on mineral surfaces.