Molecular dynamics study of interfacial properties in CO2 enhanced oil recovery

CO2 enhanced oil recovery (EOR) is a promising technique for carbon capture, utilization and storage (CCUS). Owing to the abundant distribution of nanostructure in unconventional oil reservoirs, the investigation on the interfacial properties of the CO2 and oil system in nanopores is still lacking as well as the corresponding mechanism of displacement of oil by injecting CO2 in CO2 EOR. In this study, we coupled CO2 and n-decane force fields in molecular dynamics (MD) simulations by modifying Lorentz-Berthelot combination rules to calculate key physical properties of CO2+n-decane system more accurately. The phase equilibrium and interfacial properties of CO2+n-decane binary system were studied under different pressures. Then we explored the interfacial properties of CO2+n-decane mixture in α-quartz nanopores and found that the adsorption of CO2 is stronger than n-decane, which is beneficial for displacing n-decane from the pore surface and then enhancing oil recovery. An increase in the diffusion of n-decane was observed with the increase of injected CO2, while when excess CO2 was injected, the diffusivity of CO2 and n-decane in nanopore both decreased. The underlying mechanisms of these phenomena were understood by the structure and diffusive properties in bulk and α-quartz nanopores.