Optimization of CO₂ Flooding Parameters in Ultra-Low Permeability Oil Reservoirs with High Water Cut

A numerical simulation of CO₂ flooding was conducted to determine the impact of production parameters on enhanced oil recovery. Optimizing the CO₂ flooding parameters revealed that increasing the CO₂ injection rate enhances the oil production rate but also intensifies gas channelling, reduces the oil exchange rate, and poses a risk of fracturing the formation. While an increase in bottomhole pressure may temporarily limit the oil production rate, it is beneficial in the long term as it helps to elevate formation pressure, facilitating CO₂ miscibility with reservoir oil to improve stage recovery and oil exchange rate. Bottomhole pressure should be increased as much as possible, ensuring an injection-production balance. An increase in water cut in the block diminishes CO₂ flooding effectiveness, leading to lower recovery and oil exchange rate. During CO₂ flooding development, oil exchange rate will decline with rising production gas-oil ratio. Therefore, injection wells should be shut in timely to ensure reasonable CO₂ injection amounts. Based on these findings, optimal parameters were determined: a CO₂ injection rate of 15, 000 m³/d, a production bottomhole pressure of 25 MPa, CO₂ injection timing at a block water cut of 60%, and shut-in timing when the production gas-oil ratio reaches 1 000 m³/m³, with a reasonable CO₂ injection amount of 92 000 tons. Simulation results using these optimized parameters indicated that after 9 years of CO₂ injection, crude oil production from the block increased by 213 000 tons, with a corresponding oil recovery improvement of 27.4%. The cumulative oil exchange rate reached 0.58, while the cumulative storage rate reached 0.67.