Stimulation Mechanism and Development Method Optimization of CO₂ Injection After Water Flooding in Low Permeability Glutenite Reservoir

CO₂ miscible flooding can not only improve reservoir recovery, but also achieve carbon sequestration and alleviate the greenhouse effect. However, there are few studies on the development of CO₂ flooding after water flooding in low permeability glutenite reservoirs, and the development mode and effect are not clear. This paper takes an oilfield as an example. Firstly, the main mechanism of CO₂ flooding was clarified. Then, the minimum miscible pressure and oil displacement efficiency under immiscible, near miscible and miscible conditions were determined by laboratory experiments. Finally, the development method of CO₂ miscible flooding in this area was optimized by numerical simulation and the recovery was predicted. The results show that CO₂ miscible flooding can significantly expand the swept volume while improving the oil displacement efficiency. The oil displacement efficiency of miscible flooding is higher than that of near miscible and immiscible flooding, and CO₂ miscible flooding can be realized under reservoir conditions in this area. The inverted nine-point well pattern with 350 m well spacing is suitable. It is recommended to use a gentle step gas injection method. The daily gas injection volume is 20 t/d in the formation energy supplement stage, 40–50 t/d in the miscible phase, and 60–70 t/d in the liquid extraction stage. It is expected that the recovery can reach 41.5% after 15 years, which is 22.3% higher than that of water flooding. This conclusion has guiding significance for the similar reservoirs.