Aggregation Behavior of Asphaltenes in Heavy Oil and Its Influencing Factors: A Multiscale Study Based on Molecular Dynamics Simulations and Quantum Chemical Calculations

Summary Asphaltenes and resins are important and complex components of heavy oils, and their self-aggregation behavior has a profound effect on the oil and gas industry. In this study, based on three classical molecular models of asphaltenes, the aggregation laws of asphaltenes with different structures and their influencing factors were investigated using molecular dynamics (MD) simulations and quantum chemical calculations. By analyzing the equilibrium conformations, interaction energy, radial distribution functions (RDFs), mean square displacements (MSDs), diffusion coefficients, cluster analyses, radii of gyration, electrostatic potentials, and nonbonding interactions, we found that archipelago-type asphaltenes have the strongest interactions, the highest probability of occurrence, and the best stability. In contrast, continental asphaltenes have the strongest diffusion ability in the heavy oil model. Quantum chemical calculations show that the asphaltene association is mainly driven by van der Waals forces initiated by the aromatic core and electrostatic attraction around the heteroatoms, whereas the aggregation behavior is influenced by a variety of factors, such as intermolecular van der Waals forces, hydrogen bonding, and π-π interactions. In addition, external conditions, such as temperature and pressure, considerably affect the aggregation behavior of asphaltenes. This study provides a theoretical basis for exploring the viscosity mechanism of heavy oils and scientific support for the efficient development of oil and gas fields.