Insights into the mechanism during viscosity reduction process of heavy oil through molecule simulation

Faced with the problem of high viscosity of heavy oil, revealing interaction mechanism of viscosity reduction from molecular level is of significance for scientifically designing viscosity reducers. Therefore, molecular dynamics (MD) and quantum mechanics (QM) simulations were combined to conduct a profound research on viscosity reduction mechanism of heavy oil. Three kinds of viscosity reducers (VRs) used in experiment were modeled and inserted into the heavy oil box systems constructed for simulation. By comparing average cluster sizes of asphaltenes in each system, and interactions between the characteristic atoms in the VRs’ branches and asphaltenes, the difference in the effects of different viscosity reducers were fully understood. After analyzing the π-π stacking forms among asphaltenes-asphaltenes, asphaltenes-resins, and resins-resins in different simulation systems, a potential viscosity reduction mechanism was proposed. The strong face-face stacking between asphaltenes and asphaltenes in heavy oil is converted into a relatively weaker face-face stacking of asphaltene-resin, with weak interaction type and strength among heavy oil molecules further explored. Finally, a criterion for screening solvents was put forward after investigating the property of different solvents, toluene and kerosene. Molecule simulation was carried out to reveal the mechanism for viscosity reduction of heavy oil under molecular level, which made a contribution to the exploration of heavy oil.