Gas-Solvent-Assisted CO₂ Injection for Shale Oil Recovery: Modifying Oil Properties and Enhancing Competitive Adsorption

Given the limited improvement in shale oil recovery from microscopic pores through pure CO2 injection, this study explores the potential of gas-solvent-assisted CO2 to enhance recovery by improving miscibility and displacement efficiency in shale oil. Systematic experiments revealed the interaction effects between gas-solvent-assisted CO2 and shale oil. Molecular dynamics simulations were utilized to examine the enhanced oil displacement performance and underlying interaction mechanisms. Furthermore, the role of gas solvents in augmenting CO2's competitive adsorption capabilities was explored. The research results showed that the addition of gas solvents reduces the saturation pressure of shale oil, enhances the CO2 solubility, and increases the expansion coefficient while significantly decreasing the viscosity, density, and minimum miscibility pressure (MMP). In displacement models, gas-solvent-assisted CO2 systems exhibited stronger interactions with octane and SiO2, leading to markedly improved displacement efficiency compared to pure CO2 systems and enabling faster, more complete interactions between CO2 and octane. Furthermore, competitive adsorption experiments highlight the ability of gas solvents to enhance CO2 adsorption over CH4 in nanopores, increasing selectivity coefficients and optimizing adsorption profiles. These findings provide critical insights into the potential of gas-solvent-assisted CO2 injection as a viable strategy for enhancing shale oil recovery and advancing the understanding of gas-liquid interactions in unconventional reservoirs.