Abstract
Injecting CO2 into shale oil reservoirs has the dual purpose of enhancing oil recovery rate and geological storage of CO2. The phase behavior and mass transfer laws of the CO2-shale oil are crucial for achieving highly efficient production shale oil and gas. Based on an improved vapor-liquid equilibrium (VLE) model in nanopores, which achieves a relative error of less than 3.16%, this study investigates the phase behavior and CO2–oil mass transfer laws of two representative shale oils under CO2 injection. Research results show that after CO2 injection, the saturation pressure tends first to increase and then reduce. The CO2 dissolution results in a significant reduction in the molecular weight and viscosity of Wolfcamp shale oil. During the multi-contact shale oil with CO2 injection, both density and the interfacial tension (IFT) reduce at the forward contact edge, indicating forward-contact miscibility. Furthermore, the nanoconfinement effect reduces the density difference between the liquid and gas phases, leading to a reduction in the IFT, which is beneficial for gas-oil miscibility. The study results can provide a theoretical basis for understanding compositional variations in shale oils under CO2 injection, offering promising improvements in miscibility and recovery efficiency.