Molecular dynamics investigation of shale oil occurrence and adsorption in nanopores: Unveiling wettability and influencing factors

Abstract

Shale oil, an unconventional petroleum resource, has gained significant attention in the industry. Understanding how shale oils exist in nanopores is crucial for unraveling their flow mechanisms and production prediction. The molecular dynamics simulations are conducted to explore oil occurrence and adsorption in various mineral nanopores, and the wettability and influencing factors. This study reveals a non-uniform fluid density distribution within nanopores, decreasing from the solid wall to the center. Distinct differences are observed between adsorbed and free-state oil phases. The effects of temperature, pressure, mineral type, and pore size effects on wettability, adsorption layer thickness, and molecule proportion are studied. Adsorption energy is calculated using physicochemical methods. Findings show temperature and mineral properties primarily influence shale oil wettability, with less impact from pressure. Adsorption capacity and layer thickness are affected by temperature, mineral type, and size. Octane distribution in nanopores is non-uniform, with a 1.5–1.75 nm layer on non-polar mineral walls and 0.67–1.35 nm on polar minerals. A positive correlation exists between shale oil adsorption on mineral nanopores, layer thickness, and adsorption energy. This study enhances our understanding of oil behavior in nanopores of shale oil reservoirs.