Molecular Dynamics Investigation of CO2/H2O/N2-Assisted Shale-Oil Displacement in Quartz Nanopores Under Nanoconfinement

Molecular dynamics simulations are employed to investigate the displacement behavior of shale oil by the CO2/H2O/N2 multicomponent thermofluid in α-SiO2 slit nanopores under various temperature and pressure conditions. The results demonstrate that increasing pressure effectively promotes crude oil displacement, and this promoting effect exhibits a pronounced pore-scale dependence: at 413 K, as pressure increases from 10 to 40 MPa, the displacement amounts in 4–10 nm pores rise from 1.65–1.81 mmol/g to 1.87–2.08 mmol/g, with larger pores showing more pronounced pressure-induced gains. Increasing temperature continuously enhances displacement, but the degree of promotion shows a non-monotonic dependence on pore width: at 20 MPa, as temperature increases from 393 to 513 K, the displacement amounts in 4–10 nm pores increase by 14.3–19.5%, with the 4 nm pore exhibiting the largest relative gain. Under identical conditions, displacement generally increases with pore width, indicating that pore width is a key structural factor governing displacement performance under nanoconfinement. Specifically, with decreasing pore width, fluid molecules experience stronger spatial constraints from mineral walls and reduced migration space, which amplifies the restrictions imposed by oil–mineral interfacial interactions on crude oil migration. In contrast, larger pores provide sufficient migration space for the multicomponent thermofluid, effectively mitigating the detrimental effects of nanoconfinement. Together, pressure, temperature, and pore width govern the displacement behavior of the multicomponent thermofluid through distinct but interrelated microscopic mechanisms, providing a molecular-level basis for optimizing multicomponent thermofluid injection strategies in shale oil recovery.