Competitive adsorption of asphaltene and n-heptane on quartz surfaces and its effect on crude oil transport through nanopores

Abstract

• Competitive adsorption mechanism between asphaltene and n-heptane on quartz surfaces was illustrated from molecular perspective. • Influence of asphaltene deposition on the transport of light oil is clarified. • Work of adhesion and adsorption time ratio were proposed to quantify adsorption strength. • Flow behaviors of asphaltene and n-heptane in two quartz nanopores were compared. Asphaltene deposition is a ubiquitous problem in crude oil exploitation, which can cause the blockage of pore throat, leading to a significant reduction of oil recovery. Understanding the microscopic mechanism of asphaltene deposition and its influence on the oil flow in nanopores is critical for effective exploitation of crude oil. In this study, we investigated the competitive adsorption of asphaltene and n-heptane on quartz surfaces using molecular dynamics simulations. We found that asphaltene shows a much stronger adsorption ability on the quartz surfaces than n-heptane, resulting from both interfacial energy strength and the poly-aromatic ring interactions among asphaltene molecules. With the deposition of asphaltene, the flux of n-heptane transport in nanopores is greatly decreased, which can be attributed to the reduction of effective aperture size and the disappearance of possible slip near the surface. The difference in adsorption and flow behaviors between asphaltene and n-heptane can be further elucidated by the comparison in work of adhesion for several interfaces. Besides, the effect of surface hydroxyl groups of quartz substrates was proved to have a prominent impact on the adsorption of asphaltene on the quartz surfaces, leading to a considerable enhancement of oil flux through SiO 2 nanopores. Our work advances the understanding of the low oil recovery caused by asphaltene deposition and has a significant reference value to the effective production and evaluation of crude oil.