Comprehensive Investigation for CO2 Flooding Methodology in a Reservoir with High Water Content

In response to the development challenges caused by the high initial water saturation, low porosity, low permeability, and strong heterogeneity in C tight sandstone reservoirs, a comprehensive study was conducted on the optimization of development methods using a fuzzy model, core flooding experiments, and reservoir numerical simulations. The initial evaluation indicates the good adaptability of CO2 flooding for improving oil recovery in a C reservoir; the experimental result of the CO2 displacement method also performs the best, with a recovery rate of 68.38% at a connate water saturation of about 30%, compared with surfactant flooding and water flooding. However, higher water saturation inhibits the CO2 development effect. The oil recovery factor of pure CO2 huff-n-puff is 32.24% lower than the CO2 displacement method, while surfactant-assisted CO2 huff-n-puff can increase the recovery rate by 0.85% compared to pure CO2. Based on actual geological models, numerical simulations were conducted on Well Block A and B. The results showed that the optimized production pressure is above the Minimum Miscibility Pressure (16.44 MPa); with consideration of the fracture pressure limitation, the CO2 injection rate in Block A should be less than 3000 m3/d, and the recovery rate after 10 years is only 0.48% (oil change ratio is 0.07 t/t), while the CO2 displacement rate of Block B should not exceed 7500 m3/d, and the recovery rate after 10 years can reach 27.39% (oil change ratio is 0.2 t/t). CO2 displacement is an effective development method for a C reservoir, but due to a high water content the oil change ratio is very low, indicating a low potential for further development. The research provides important references for the development of similar oil reservoirs.