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The moisture contents have significant effects on shale gas and oil adsorption and transport. In this study, the oil–water two-phase occurrence state and fluid transport in shale inorganic calcite nanopores are investigated utilizing molecular dynamics simulation. The multilayer sticking flow (negative slip) of oil and water is observed in calcite nanopores. The water bridge forms in the middle of the nanopore when water/oil ratio was high. With the decrease of water percentage, the water bridge breaks up, forming a layered structure. The flow regime changes from slug flow to laminar flow, which results in a dramatic decrease in total volume flux. The liquid–liquid slip effect between water and oil layer is observed, which has a positive effect on the enhancement of oil flow in calcite nanopore. This work reveals the two-phase configuration and flow behavior in calcite nanopores and provides the theoretical support for shale oil exploration.

It is desirable to predict the surface tension of liquid mixtures for a wide range of compositions, temperatures, and pressures, but current state-of-the-art calculations (e.g., density gradient theory) are computationally expensive. We propose a computationally simple—but accurate—semi-empirical mathematical model of surface tension for a wide variety of multicomponent mixtures, including those with a supercritical compound when coupled with an equation of state (by introducing a reduced mole fraction scaled by a critical composition). Our predictions for binary systems with one supercritical component are an average of 0.22 mN/m away from literature experimental data (466 data points), and those for systems with two subcritical components (293–333 K) are within 0.09 mN/m (236 data points). We make predictions for methanol + ethanol + water using binary coefficients within an average of 0.71 mN/m (196 data points). Given its computational simplicity and wide applicability, the proposed model will be useful for many applications.

To predict phase behavior of a pure component in nanopores, various versions of Kelvin equations and equation-of-state-with-capillary-pressure (EOS–Pcap) models have been used. There has been debate on the validity of Kelvin equation, especially in sub-10-nm pores. For EOS–Pcap models, numerical iterations have been used to obtain vapor–liquid equilibrium (VLE). In slit pores with widths larger than 8 nm, the Kelvin equation agrees with (within 10%) the equilibrium vapor-phase pressures of confined propane from engineering density functional theory between 310 K and 360 K. We introduce a graphical method using pressure–volume, chemical-potential–density, and chemical-potential–pressure relations to obtain VLE using EOS–Pcap model. While the Kelvin equation takes only surface tension as an input and returns a solution for VLE up until the bulk critical point (CP), the EOS–Pcap model predicts a limiting temperature different from the bulk CP. The predictions from Kelvin equations and EOS-Pcap models can be improved by considering adsorption layer thickness.