Experimental Study on Miscible Phase and Imbibition Displacement of Crude Oil Injected with CO2 in Shale Oil Reservoir

Jimsar shale oil in China has undergone a rapid decline in formation energy and has a low recovery rate, with poor reservoir permeability. CO2 injection has become the main method for improving oil recovery. Pre-fracturing with CO2 energy storage in Jimsar shale oil has been performed, yielding a noticeable increase in oil recovery. However, the CO2 injection mechanism still requires a deeper understanding. Focusing on Jimsar shale oil in China, this paper studies the effect of CO2 on crude oil viscosity reduction, miscible phase testing, and the law of imbibition displacement. The results show that CO2 has a significant viscosity reduction effect on Jimsar shale oil, with a minimum miscible pressure between CO2 and Jimsar shale oil of 25.51 MPa, which can allow for miscibility under formation conditions. A rise in pressure increased the displacement capacity of supercritical CO2, as well as the displacement volume of crude oil. However, the rate of increase gradually declined. This research provides a theoretical basis for CO2 injection fracturing in Jimsar shale oil, which is helpful for improving the development effects of Jimsar shale oil.