Energetics and Structural Behavior of Asphaltene Molecules near Mica Surface: Molecular Simulation Study

摘要

The deposition of high asphaltene-containing crude oil on mineral surfaces and pipelines is a technical as well as an economic problem in the oil industry. In enhanced oil recovery techniques, additives and emulsifiers are used to detach oil from the mineral surface. It requires detailed knowledge of the type of interaction taking place at the molecular level between the rock surface and the crude oil to target the most dominant interacting part for site-specific design of emulsifiers. In this work, we have studied energetics of saturate and asphaltene molecules of crude oil with mica mineral surfaces in the presence of dodecane solvent using molecular dynamics simulations. Five different types of asphaltene molecules (three island type and two archipelago type) containing one heteroatom (oxygen, nitrogen, and sulfur) were considered in this study. We have calculated the potential of mean force using an umbrella sampling technique. The adsorption free energy of saturate molecules is significantly lower compared to asphaltene molecules because of the presence of the heteroatom. Asphaltene molecules with a polar heteroatom (oxygen and nitrogen) interact with mica surface strongly as compared to asphaltene molecules with a nonpolar heteroatom (sulfur). The structural behavior of asphaltene molecules at the mica-oil interface is governed by the balance of enthalpic interactions between aromatic core atoms and the steric hindrance of aliphatic chain atoms with the mica surface. Asphaltene molecules with smaller aliphatic chains are arranged parallel to the mica surface. In contrast, those molecules which have more and bigger aliphatic chains were found to have their aromatic core tilted to the mica surface. This detailed information would be useful for designing better additives to displace heavy and residual oil from the rock surface.