Molecular Dynamics Numerical Simulation of Adsorption Characteristics and Exploitation Limits in Shale Oil Microscopic Pore Spaces

Microscopic pore structure in continental shale oil reservoirs is characterized by small pore throats and complex micro-structures. The adsorption behavior of hydrocarbons on the pore walls exhibits unique physical and chemical properties. Therefore, studying the adsorption morphology of hydrocarbon components in nanometer-sized pores and clarifying the exploitation limits of shale oil at the microscopic level are of great practical significance for the efficient development of continental shale oil. In this study, molecular dynamics simulations were employed to investigate the adsorption characteristics of various single-component shale oils in inorganic quartz fissures, and the influence of pore size and shale oil hydrocarbon composition on the adsorption properties in the pores was analyzed. The results show that different molecules have different adsorption capacities in shale oil pores, with lighter hydrocarbon components (C6H14) exhibiting stronger adsorption abilities. For the same adsorbed molecule, the adsorption amount linearly increases with the increase in pore diameter, but larger pores contribute more to shale oil adsorption. In shale pores, the thickness of the adsorption layer formed by shale oil molecules ranges from 0.4 to 0.5 nm, which is similar to the width of alkane molecules. Shale oil in the adsorbed state that is difficult to be exploited is mainly concentrated in the first adsorption layer. Among them, the volume fraction of adsorbed shale oil in 6 nm shale pores is 40.8%, while the volume fraction of shale oil that is difficult to be exploited is 16.2%.