Mechanisms and Production Enhancement Effects of CO 2 /CH 4 Mixed Gas Injection in Shale Oil

Shale oil, a critical unconventional energy resource, has received substantial attention in recent years. However, systematic research on developing shale oil using mixed gases remains limited, and the effects of various gas compositions on crude oil and rock properties, along with their potential for enhanced oil recovery, are not yet fully understood. This study utilizes PVT analysis, SEM, and core flooding tests with various gas mixtures to elucidate the interaction mechanisms among crude oil, gas, and rock, as well as the recovery efficiency of different gas types. The results indicate that increasing the mole fraction of CH 4 substantially raises the oil saturation pressure, up to 1.5 times its initial value. Pure CO 2 , by contrast, exhibits the lowest saturation pressure, rendering it suitable for long-term pressurization strategies. CO 2 shows exceptional efficacy in reducing interfacial tension, though the viscosity reduction effects of different gases exhibit minimal variation. Furthermore, CO 2 markedly modifies the pore structure of shale through dissolution, increasing porosity by 2% and enhancing permeability by 61.63%. In both matrix and fractured cores, the recovery rates achieved with mixed gases were 36.9% and 58.6%, respectively, demonstrating improved production compared to single-component gases. This research offers a theoretical foundation and novel insights into shale oil development.