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

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.

Automated summary

CO2 miscible flooding in low permeability reservoirs can significantly improve oil recovery. Current research mainly focuses on the simulation of seepage process in CO2 miscible flooding, while lacking pressure control and characterization of CO2 concentration diffusion. In this study, a numerical model of CO2 miscible flooding is established and the microscopic seepage characteristics of interphase mass transfer are analyzed. The effects of injection velocity, contact angle, diffusion coefficient, and initial injection concentration on the seepage characteristics and concentration distribution of CO2 miscible flooding are investigated. The results show that CO2 preferentially diffuses into the large pore space and forms a miscible area with crude oil through interphase mass transfer. The increase in injection velocity accelerates the seepage process and expands the sweep area. The increase in contact angle increases the seepage resistance and decreases the recovery efficiency. The increase in diffusion coefficient leads to higher CO2 concentration in small pores. The larger the initial injection concentration, the higher the CO2 concentration in the large pore and miscible areas. This study provides guidance for understanding the microscopic seepage characteristics of CO2 miscible flooding.