Research on the Mechanism of CO2-Oil Diffusion Impacting Oil and Gas Seepage Law in CCUS-EOR Process

Abstract

Abstract In the process of enhanced oil recovery by CO2 huff and puff, the influence of gas diffusion effect cannot be ignored. In this paper, based on Fick's law and Buckley–Leverett equation, the fractional flow equation and the relative permeability model of oil and gas considering gas diffusion are established. The influence of diffusion on oil and gas seepage law is revealed from two aspects of partial flow curve and oil and gas relative permeability curve, and the influence mechanism of miscible degree and alkane type on oil and gas relative permeability curve is further analyzed. The results show that after considering the effect of gas diffusion, the relative permeability of oil phase increases and the relative permeability of gas phase decreases. The influence of gas diffusion on the relative permeability curve of oil and gas gradually decreases with the decrease of oil saturation. Diffusion will delay the advance speed of the oil and gas seepage front, and increase the gas saturation of the front. With the increase of miscible degree, the relative permeability of oil and gas increases, the two-phase seepage area becomes wider, and the residual oil saturation decreases. With the increase of alkane carbon number, the relative permeability of oil and gas phases decreases, the two-phase seepage area narrows, and the residual oil saturation increases. This study clarifies the influence of diffusion effect on the seepage behavior of oil and gas, and provides a new theoretical basis for the implementation of CCUS-EOR project.