Study on the microscopic mechanism of CO ₂ flooding in deep high-temperature, high pressure, ultra-high water-cut reservoirs: a case study of the X-1 reservoir

Deep high-temperature, high-pressure, ultra-high water-cut reservoirs face a series of problems, such as rapid production decline, fast water invasion rate, and low sweep efficiency. Therefore, it is urgent to change the development mode and further improve recovery efficiency. In this work, a novel micro-visualization experimental method was developed to elucidate the micro-displacement mechanisms in CO₂ injection reservoirs. <i>In situ</i> nuclear magnetic resonance experiments were employed to assess micro-scale sweep efficiency. The results showed that CO₂ could effectively expand microscopic sweep efficiency, significantly improve crude oil mobilization in medium and large pores, and slightly mobilize previously unrecoverable oil in small pores, thereby effectively reducing remaining oil saturation and increasing displacement efficiency by 12.8%.