The reserves of shale oil are abundant in China and have broad development prospects. However, shale oil is mainly stored in micro-nanopores with low permeability and porosity, resulting in a poor mobility and low recovery for the crude oil. Under severe confined conditions, the complex interactions between oil, formation water and rock surface is dominant. To elucidate the mechanical mechanisms of rock/oil interfacial interaction and their effects on fluid transport in micro-nanopores is not only a key scientific problem, but a significant foundation of enhanced oil recovery (EOR). Generally, the interactions between crude oil and rock surfaces can be divided into direct and indirect interactions. The former is the direct adsorption of oil molecules on rock surface, while the latter is the complex bridging interactions between polar oil molecules and rock surface through a thin brine film.

This work focuses on the microcosmic mechanical interactions of rock/brine/oil interface and nanoscale transport behavior during crude oil exploitation process. Based on the molecular dynamics (MD) simulations, the migration and recovery behavior of multi-component shale oil in blind pores through a pore throat was first investigated. We found that the heavy fraction has a significant inhibition effect on the gas/oil mixture recovery. Four inhibition mechanisms were summarized as edge adsorption, surface adsorption, throat plugging and liquid bridge. The heavy fraction molecules tend to migrate in the form of oil clusters, and the dependence between the critical size of pore plugging and oil cluster size was illustrated. On this basis, we investigated the effects of asphaltene on the transport of light components through quartz nanopores. It turned out that the asphaltene molecules can form multilayered stacked adsorption structures near the pore surface, resulting in a significant reduction of the flux through nanopores. It can be attributed to the decrease of effective pore size and the disappearance of solid/liquid and liquid/liquid slip near the surface. Except for the heavy fraction in crude oil, the presence of brine films on rock surface can also significantly affect the oil transport in nanopores, which is mainly due to the strong bridging interactions between polar groups and hydration ions near the rock/brine/oil interfacial region. The relationship between the interaction strength of single carboxylic acid molecules and ions was proved to be able to extend to illustrate the difference of flow behavior in nanopores. Furthermore, a strategy that monovalent cations with higher concentration replaces divalent cations to weaken the interaction between rock/brine/oil was further proposed and verified. Our study sheds light on the rock/oil interfacial interactions and its microscopic mechanisms affecting oil flow, and also provides significant insights for low-salinity water flooding.