Adsorption layer of complex oil components in organic-rich shale: A molecular dynamics simulation study

Abstract

Shale oil is enriched in organic-rich shale, and its reservoir is mainly composed of micro-nano pore throats. The fluid adsorption layer in nano-confined channels complicates the fluid properties and transport patterns. In this study, equilibrium molecular dynamics was used to study the distribution states and diffusion patterns of complex oil components in organic matter represented by kerogen and four inorganic minerals represented by illite, quartz, calcite, and albite. The thickness and proportion of adsorption layers with different pores are quantitatively calculated. The adsorption capacity is in the following order: kerogen > illite > albite > calcite > quartz. According to the interaction energy, the adsorption stability of oil on surfaces with different pores is in the following order: illite > albite > calcite > kerogen > quartz, and the main forces of adsorption with different pores are obtained. With the increase in pore size, the proportion of light components in the adsorption layer increases, and the proportion of heavy components decreases. The oil components in quartz, calcite, and albite gradually desorb with the increase of pore size, while the oil components in illite are the opposite. The adsorption proportion of other components except for toluene in the kerogen pore increased. The diffusion rate of components in kerogen, quartz, and calcite is related to their relative atomic mass. The diffusion coefficient of components in illite is related to the polarity of components. The diffusion rate of components in small pore sizes of albite minerals is related to the polarity of components, and the diffusion rate of components in large pore sizes is related to the relative atomic mass of components. The effect of temperature and initial moisture content on pores is related to the type of pores.