The mass transfer behaviors and mechanisms of CO2–oil phase in quartz confined nano-space: Insights from molecular dynamics simulations

The mass transfer process of CO2 multiphase systems constitutes a core physical mechanism governing both oil recovery and sequestration performance, involving complex interactions between CO2 and oil under reservoir conditions. However, the mass transfer behavior of CO2 multiphase systems at the nanoscale remains insufficiently elucidated. This study investigates the transport and mass transfer processes of CO2 multiphase systems within nanopores using molecular dynamics simulations, specifically focusing on the underlying CO2–oil interaction mechanisms and the influence of various factors. The results demonstrate that the energy difference between CO2–oil phase and oil phase–pore wall interactions serves as the decisive factor for mass transfer behaviors, with larger energy differences correlating to enhanced miscibility effects. Van der Waals energy dominates the CO2–oil interaction energy and acts as the primary driving force for interphase mass transfer. Elevated temperature and pressure significantly promote the mass transfer process. CO2 exhibits superior mass transfer behaviors with nonpolar oil molecules compared to polar counterparts, and shorter-chain nonpolar molecules achieve better miscibility with CO2. Hydrocarbon gases can promote the mass transfer process between CO2 and C8H18, and impurity gases inhibit mass transfer. The mass transfer degree of CO2 and C8H18 increases with nanopore size and reaches higher levels in hydrophilic pores. These findings provide molecular-level insights into CO2–oil mass transfer behaviors, offering theoretical guidance for optimizing CO2-enhanced oil recovery and geological sequestration strategies.