纳米限域对页岩油-CO2体系相行为的影响OA

Studying the phase behavior of the oil-CO2 system is crucial for efficient shale oil and gas recovery.Considering the effects of capillary pressure and the shift of fluid critical points,a vapor-liquid equilibrium(VLE)model incorporating nano-confinement effects was developed,achieving a prediction relative error of less than or equal to 1.53%.On this basis,the phase behavior of CO2-shale oil systems was investigated using Eagle Ford and Wolfcamp shale oils as examples.The results indicate that the presence of nano-confinement suppresses the bubble-point pressure and delays gas liberation from the liquid phase,resulting in a lower gas-oil ratio,which is favorable for shale oil production.Under nano-confinement,the reduced gas-liquid density difference leads to a decrease in gas-liquid interfacial tension.Smaller pore radius of reservoir correspond to stronger nano-confinement effects and a greater tendency for CO2 and oil to become miscible.As the pore radius decreases,the gas-liquid interfacial tension first decreases slowly and then rapidly,with a pore radius of 20 nm identified as the turning point.In contrast,the capillary pressure first increases and then decreases,with the turning point occurring at a pore radius of 5 nm.This study can provide a reference for optimizing CO2 injection strategies and enhancing shale oil recovery.