Experimental Study on Supercritical CO2 Enhanced Oil Recovery in Tight Reservoirs - Taking L Block as an Example

Abstract

In order to solve the problem of fast decline in oil production and inability to maintain reservoir pressure in the L block of Cao She oilfield, a supercritical CO₂ injection and production experiment was conducted using a real rock core sample to explore the feasibility of using supercritical CO₂ flooding for enhanced oil recovery. The experiment was conducted on a long rock core sample after the reservoir had reached its decline stage. The effects of important operational parameters such as the number of flooding cycles, shut-in time, CO₂ injection volume, and adding surfactant flooding on enhancing oil recovery were studied. The results show that supercritical CO₂ flooding can effectively enhance oil recovery, with the best development effect in the first three flooding cycles, accounting for about 90% of the total oil recovery. There is a reasonable shut-in time for CO₂ flooding, and under certain conditions, prolonging the shut-in time can improve oil recovery to some extent. The oil recovery rate increases gradually with the increase of CO₂ injection volume. The oil recovery rate in the surfactant flooding experiment was 26.06%, which was 29.7% higher than the oil recovery rate in the flooding production experiment. Adding surfactant reduces the interfacial tension between oil and water and the starting pressure, improves the wetting properties of the reservoir rock, enhances the capillary imbibition and oil-water displacement ability of the matrix pore. The research results confirm the feasibility and huge application potential of injecting supercritical CO₂ for enhanced oil recovery, and can provide theoretical basis and technical support for the efficient development of the L block of Cao She oilfield.