Study on the Effect of CO2 and Seepage Enhancer Composite Drive on Enhanced Oil Recovery in Oil Reservoirs

In view of the large reserve base of the implemented CO2 drive development block, there is still a large amount of residual crude oil underground after the first CO2 drive, and the CO2 drive suitability is high, which has the potential to further improve the oil recovery of the reservoir. In this paper, the mechanism of imbibition synergist, CO2 and compound displacement to improve crude oil recovery is studied by carrying out displacement experiments of formation water, imbibition synergist, CO2, CO2/formation water and CO2/imbibition synergist. The effect of different slug sizes and gas-water ratios on gas-water alternating composite displacement is clarified. The experimental results show that the addition of imbibition synergist solution to formation water enhances spontaneous imbibition in the process of displacement, and the oil recovery is 9% higher than that of pure formation water displacement, and the effect of CO2 displacement is better than that of imbibition synergist. The oil recovery of CO2/imbibition synergist compound displacement is 14% higher than that of CO2/formation water compound displacement. This is because CO2/imbibition synergist compound displacement adds imbibition synergist to the water slug when gas and water is alternating, which enhances the spontaneous imbibition of small pores. The imbibition synergist solution will weaken the flow ability of CO2 in the formation, avoid the occurrence of CO2 rapid gas channeling, and further improve the efficiency of oil washing. Different slug sizes and gas-water ratios have different effects on composite displacement. Therefore, the composite displacement method can greatly improve the wettability and spontaneous imbibition while reducing the oil-water interface tension, which solves the problem that CO2 cannot enter small pores in a low pressure differential environment, and improves the final oil recovery. It has important guiding significance for the development of reservoirs suitable for using CO2 drive to further enhance oil recovery.