A Method for Determining the CO₂-Crude Oil Relative Permeability Curve Considering Gas Diffusion Effects

Oil-gas relative permeability is a key parameter that characterizes the flow characteristics of oil and gas through the porous media of a reservoir. The existing JBN model used to determine the oil-gas relative permeability curve via unsteady-state methods neglects the impact of gas diffusion. However, during reservoir development, the influence of gas diffusion cannot be overlooked. An improved relative permeability model incorporating the effect of gas diffusion is developed based on Fick's law, Darcy's law, and the material balance equation. The relative permeability curves of CO₂-crude oil obtained by this model and JBN model are compared, demonstrating the impact of diffusion on the oil-gas relative permeability. Results show that when gas diffusion is taken into account, the relative permeability of the oil phase increases, whereas the relative permeability of the gas phase decreases. The relative permeability difference of oil and gas before and after considering gas diffusion effect is between 6% and 38%, and decreases with the decrease of oil saturation. The degree of influence depends on the diffusion coefficient of CO₂-crude oil. Incorporating gas diffusion into the oil-gas relative permeability model provides a more accurate representation of flow characteristics, providing new insights into the mechanisms of CO₂ huff and puff to enhance oil recovery.