Adsorption Characteristics of Alkanes with Different Carbon Numbers in Kaolinite Slits

Abstract

Shale oil is of interest for unconventional oil and gas exploration and development and has abundant geological reserves. Shale reservoirs contain numerous nanopores. Understanding the adsorption state of shale oil in the nanopores of shale is beneficial to improve the recovery of shale oil. In this study, the adsorption properties of shale oil in kaolinite slit pores were investigated by molecular dynamics simulation. In order to study the adsorption characteristics of shale oil with different components, a single-component model from n-C8 to n-C15 was established, and a mixed model of n-C8 and n-C15 with different mass ratios represented different crude oil components. The results show that the adsorption capacity per unit area increases with the increase of the alkane carbon number. The adsorption capacity of alkanes on the surface of silicon-oxygen tetrahedron is greater than that on the surface of aluminium-oxygen octahedron. The interaction force between kaolinite and alkane surface increases with the increase of alkane carbon number. The alkane adsorption capacity of silicon-oxygen tetrahedron is stronger than that of aluminium-oxygen octahedron. Competitive adsorption also exists between alkane molecules. Alkanes with higher carbon numbers are more easily adsorbed on the surface of kaolinite. Light alkanes are more likely to exist in free form than heavy alkanes. Based on molecular simulations, we studied the adsorption capacity of alkanes with different carbon numbers and calculated the adsorption capacity per unit area in the pores. It provides a theoretical basis for the calculation of shale oil geological reserves.