Decoding Microscopic Storage Mechanisms of Shale Oil and Its Influencing Factors

This study employs molecular dynamics (MD) simulations and Grand Canonical Monte Carlo (GCMC) methods to elucidate the microscopic storage mechanisms of shale oil in both hydrated and dry shale pores, as well as the key factors influencing these mechanisms. Molecular models were established for organic matter (kerogen), brittle minerals (quartz and feldspar), carbonate minerals (calcite), clay minerals (illite, kaolinite, and montmorillonite), and graphite to analyze density distributions, adsorption behaviors, and competitive adsorption under water-bearing conditions. The results reveal that shale oil forms up to three adsorption layers (0.4–0.5 nm) near pore walls, with adsorption capacity governed by pore size, temperature, pressure, and alkane composition. The adsorption affinity follows the order: toluene > hexanoic acid > dodecane > propylene > n-octane > n-pentane, while wall material preference ranks as kaolinite > graphite > montmorillonite > illite > feldspar > calcite > quartz. In water-bearing shale, pore water regulates shale oil occurrence in montmorillonite pores through competitive adsorption and spatial exclusion. Increasing water content promotes the formation of stable hydration layers, which occupy adsorption sites and weaken oil–mineral interactions, thereby markedly inhibiting shale oil adsorption and enrichment. These findings provide theoretical guidance for shale oil evaluation and development.