Study on Advanced CO2 Gas-Water Alternating Injection for the Development of Mesoporous Ultra-Low Permeability Oil Reservoirs

The Fuyu oil formation in Xingbei Oilfield has an average porosity of 15.1% and an average permeability of 4.06 × 10−3μm2, which is a typical medium-porosity and extra-low permeability reservoir. The overall production after water injection shows the problems of poor injection efficiency, high water content and low recovery rate, etc. In order to improve the development effect, numerical simulation is applied to simulate the production of Fuyu oil reservoir. In order to improve the development effect, numerical simulation was applied to simulate the oil enhancement effect of CO2 drive, CO2 gas-water alternating drive and over-injection of CO2 and then gas-water alternating drive, and optimize the parameters such as gas injection rate, gas-water ratio and alternating cycle. The results show that: CO2 gas-water alternating drive has the outstanding features of preventing gas flushing, good oil enhancement effect and low economic cost; over-injection of CO2 plays the key role of energy replenishment and phase mixing, and solves the problem of poor efficiency of water injection, and determines the injection and extraction scheme of 5-point method mode, 1-year turn cycle and 1:1 gas-to-water ratio, which realizes the cumulative gas injection volume of 4.16 × 104t, cumulative oil enhancement of 2.10 × 104m3, and the conversion rate of oil exchange of 0.5 × 104m3, and the conversion rate of oil exchange of 0.0 × 104m3. The oil exchange rate was 0.5036m3/t. The proposed over-injection of CO2 has achieved a better development effect. The proposed gas-water alternating drive development method with over-injection of CO2 has important reference value for exploiting the medium-hole extra-low permeability reservoir, and is also of practical significance for the utilization and storage of CO2 under the background of carbon neutrality.