Multi-component oil-water two phase flow in quartz and kerogen nanopores: A molecular dynamics study

Two-phase flow of oil and water frequently occurs within shale nanopores. Unique phenomena, like liquid-liquid slip at the oil-water interface, have been noted within the alkane-water system. However, in the case of realistic crude oil, the presence of highly polar components like asphaltene and toluene may introduce intricate migration behaviors near phase interfaces. Consequently, it is imperative to thoroughly explore the influence of these realistic crude oil components on flow behavior. This paper employs a comparative approach to examine the impact of polar components present in crude oil on two-phase nanoflow by molecular dynamic simulations. The investigation employs a mixed alkanes model (encompassing methane, propane, octane, and tetradecane) and a black oil model (comprising a range of alkanes, toluene, and asphaltene) to analyze the behavior of oil-water two-phase flow within quartz and kerogen nanopores, respectively. Four water adsorption layers near the quartz with an individual thickness of 0.23 nm and three alkane adsorption layers near the kerogen surface with an individual thickness of 0.45 nm were observed. Near the oil-water interface region, it indicated that toluene and asphaltene tend to accumulate, leading to a reduction of alkane aggregation in that region. Such aggregation of toluene and asphaltene imparts an interfacial viscosity increase of 2.67 to 3.47 times, substantially diminishing the enhancement of liquid-liquid slip. Based Hagen-Poiseuille equation, we proposed a simplified mathematical model in which the liquid-liquid slip was neglected and the oil-water interface region was omitted. Compared with the results from molecular dynamic simulations, such a simplified model is validated and effective for the description of oil-water two-phase nanoflows containing toluene and asphaltene, and ensures that the relative error of flow rate remains below 0.5 %. This study provides valuable insights into the two-phase flow of oil-water in nanopores, particularly measuring the effect of liquid-liquid slip under the different crude oil components conditions.