A molecular dynamics approach to investigate effect of pressure on asphaltene self-aggregation

Asphaltene aggregation is a serious issue in the oil industry that negatively affects the production, trans-portation, and exploitation of oil, causing considerable costs. In the past few years, the experimental anal-ysis of asphaltene aggregation has been a fascinating topic; however, a laboratory study that can assess the asphaltene aggregation behaviors at high pressures will be a costly and high-risk project. In this paper, molecular dynamics (MD) simulations are used to investigate the influence of pressure on the asphaltene aggregation phenomenon. The employed asphaltene in this research is Gachsaran asphaltene (obtained from an Iranian oilfield) with archipelago geometry. The aggregation number, radial distribu-tion function (RDF), potential of mean force (PMF), cohesive energy, solubility parameter, mean square displacement (MSD), diffusion coefficient, relative concentration, potential energy, and radius of gyration are analyzed based on the data and results obtained from the output trajectory files. It is concluded that the number and the average size of asphaltene aggregates significantly decrease with increasing pressure because the pressure delays the growth of asphaltene aggregates by enhancing the asphaltene solubility parameter. The associated energies of asphaltene molecules at 35, 90, and 135 bar are calculated to be-15.7834,-15.7571, and-15.7249 kJ / mol, respectively. It is found that the tendency of asphaltene molecules to aggregate reduces upon an increase in pressure. Face-to-face interactions are more likely than T-shaped and offset stacking for this asphaltene sample because of the more aromatic nuclei in the asphaltene structure than the aliphatic chains, which increase the strength of the 7C-7C interactions. It is also observed that by increasing pressure, the movement and vibration of asphaltene increase and then decrease by further increase in pressure. According to the asphaltene onset envelope diagram, the asphaltene molecules at 35 bar are located in the solid-liquid region. As the pressure increases to 90 bar, the asphaltene passes the upper asphaltene onset point zone. It can be concluded that when asphaltene is in the solid-liquid region, the mobility and displacement of molecules increase with increasing pressure. In the upper asphaltene onset point zone, the tendency of molecules to move is reduced. The MD results are consistent with the laboratory data.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

In this study, molecular dynamics (MD) simulations were used to investigate the influence of pressure on asphaltene aggregation. The results showed that the number and size of asphaltene aggregates decreased significantly with increasing pressure, due to the delay in aggregate growth and enhanced solubility parameter. Additionally, the molecular interactions and movement of asphaltene were found to change with pressure. The MD results were consistent with laboratory data.