Volume 53

Synergistic mechanism analysis of CO₂-gravity displacement based on microfluidic and NMR experiments Sun Yu, Li Yiqiang, Qi Huan, Cao Jinxin, Tang Xuechen

Abstract

CO₂ gravity flooding is an effective method to enhance oil recovery by gas flooding. In order to clarify the synergistic effect degree of gravity differentiation and oil-gas mixing relative to EOR in the process of CO₂ gravity flooding and the oil displacement mechanism, physical simulation experiments were carried out to compare and analyze the differences of different displacement processes through microscopic visualization experiments, and to clarify the microscopic application rules. Through nuclear magnetic resonance (NMR) on-line displacement experiment, the contribution ratio of extraction degree in each level of pore throat was quantitatively divided, the lower limit of critical utilization of pore throat was defined, and the synergistic development effect was evaluated. The results show that miscibility and gravity differentiation can play a synergistic role at the same time to achieve the highest recovery rate (79.08%). Compared with immiscible horizontal CO₂ flooding, oil-gas miscible effect can reduce interfacial tension, delay gas breakthrough (0.68 PV to 0.79 PV), and lower the critical pore utilization limit (0.09 μm to 0.015 μm). The degree of utilization of pore throat under 0.1 μm was increased from 3.08% to 19.79%; Gravity differentiation can improve the transverse sweep effect during the oil and gas miscible zone moving down the displacement direction. At the same time, gravity flooding can improve the utilization degree of CO₂ on small pores by increasing the injection and production pressure difference.

Keywords CO₂ gravity flooding, oil-gas miscibility, gravity differentiation, micropore throat mobilization.