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.