Interactions at the oil/brine/rock interfaces play a pivotal role in the mobility of crude oil within reservoir matrices. Unraveling the microscopic mechanisms of these interactions is crucial for ion-engineered water flooding in secondary and tertiary oil recovery. In this study, the occurrence and transport behavior of crude oil in kaolinite nanopores covered with thin brine films was investigated by molecular dynamics simulation. There is an apparent interface layered phenomenon for the liquid molecules in slit pores and the polar oil components primarily concentrate at the oil/brine interfacial region and form various binding connections with ions. The interfacial interactions between the polar oil components and brine ions exhibit an inhibitory effect on the transport of crude oil through nanopores. The interaction mechanism between acetic acid molecules and hydrated ions was elucidated by interaction modes and interaction intensity, which was proved to illustrate the flow difference in different brine film systems. Moreover, a strategy of exchanging the binding sites of divalent cations with acetic acid molecules by monovalent cations with a higher concentration was proposed. The cation exchange scheme was further validated, demonstrating an enhancement in the oil mobility within nanopores. These findings deepen our understanding of oil/brine/rock interfacial interactions and provide a significant molecular perspective on ion-engineered water flooding for enhanced oil recovery.

Understanding molecular interactions between oil and reservoir matrix is crucial to develop a productive strategy for enhanced oil recovery. Molecular dynamics simulation has become an important method for analyzing microscopic mechanisms of some static properties and dynamic processes. However, molecular modeling of shale oil and reservoir matrix is still challenging, due to their complex features. Wettability, which is the measurement of oil-matrix interactions, requires in-depth understanding from the microscopic perspective. In this study, the density, interfacial tension and viscosity of eleven common components in shale oil are calculated using molecular dynamics simulations. Then a molecular model of Gulong shale oil is built, based on the reported experimental results and simulations. Compared with the variation in hydrocarbon content, the change in polar component content leads to more significant variations in the physical properties of shale oil. This molecular model is also employed to investigate the wettability of shale-oil nanodroplets on minerals and organic matter, with or without the surrounding aqueous phase. This work suggests fresh ideas for studying the oil-matrix interactions on the nanoscale and provides theoretical guidance for shale oil exploitation.