Simulation of Microscopic Seepage Characteristics of Interphase Mass Transfer in CO2 Miscible Flooding under Multiphysics Field Coupling Conditions

Abstract

CO₂ miscible flooding in low permeability reservoirs is conducive to significantly improving oil recovery. At present, the microscopic displacement simulation of CO₂ miscible flooding is mainly reflected in the simulation of the seepage process, but the pressure control of the seepage process is lacking, and the simulation of the characterization of CO₂ concentration diffusion is less studied. In view of the above problems, a numerical model of CO₂ miscible flooding is established, and the microscopic seepage characteristics of interphase mass transfer in CO₂ miscible flooding are analyzed by multiphysics field coupling simulations at the two-dimensional pore scale. The injection velocity, contact angle, diffusion coefficient, and initial injection concentration are selected to analyze their effects on the microscopic seepage characteristics of CO₂ miscible flooding and the concentration distribution in the process of CO₂ diffusion. The research shows that after injection into the model, CO₂ preferentially diffuses into the large pore space and forms a miscible area with crude oil through interphase mass transfer, and the miscible area expands continuously and is pushed to the outlet by the high CO₂ concentration area. The increase in injection velocity will accelerate the seepage process of CO₂ miscible displacement, which will increase the sweep area at the same time. The increase in contact angle increases the seepage resistance of CO₂ and weakens the interphase mass transfer with crude oil, resulting in a gradual decrease in the final recovery efficiency. When the diffusion coefficient increases, the CO₂ concentration in the small pores and the parts that are difficult to reach at the model edge will gradually increase. The larger the initial injection concentration is, the larger the CO₂ concentration in the large pore and miscible areas in the sweep region at the same time. This study has guiding significance for the field to further understand the microscopic seepage characteristics of CO₂ miscible flooding under the effect of interphase mass transfer.