Abstract: In response to the unclear understanding of the synergistic mechanism of CO₂-C₂H₆ and the variation in miscibility during the tight reservoir development,high-temperature and high-pressure PVT device was utilized to conduct oil and gas phase behavior and extraction experiments.The study investigated the phase behavior and extraction characteristics between CO₂-C₂H₆ mixture and crude oil,and simulated the occurrence status and the mixed-phase pressure change characteristics by molecular dynamics.The study shows that:compared with the injection of CO₂ only,the addition of ethane results in a decrease of about 0.1% in the high carbon molecular weight percentage of crude oil.Ethane can effectively enhance the extraction capability of the injected gas on crude oil,transforming high carbon hydrocarbons into lower carbon hydrocarbons such as C₅.Both CO₂ and CO₂-C₂H₆ mixture are capable of extracting C₂,C₄,and C₆ from multi-component oil molecules into the gas phase,lowering the intermolecular forces in the oil phase and enhancing the mobility of crude oil.The diffusion and miscibility capabilities of the gas mixture in crude oil are stronger than those of pure CO₂.The gas mixture is more likely to form miscibility with crude oil,thereby increasing the degree of oil production.This study provides theoretical guidance for the synergistic enhanced recovery technology of CO₂-C₂H₆ gas mixture injection in tight oil reservoirs.

Key words: tight oil, molecular simulation, extraction, diffusion coefficient, CO₂-C₂H₆ mixture