Abstract:

Heavy oil is an extremely complex colloidal system where asphaltenes, as the core of micelles, are dispersed in the continuous phase of other saturated fractions. We used dissipative particle dynamics (DPD) to simulate the mesoscopic colloidal structure of heavy oil and to determine its effective factors. Coarse-grained DPD model molecules were constructed in accordance with molecular structures of the component fractions in heavy oil. A modification of the standard DPD program was used to calculate the motion of rigid polycyclic aromatic rings. The simulations show that the coarse-grained DPD models used in this paper predict the colloidal structure of heavy oil well. The ordered structure of micelles depends greatly on the molecular structure of asphaltenes. Higher ordered micelles contain highly fused aromatic rings whereas the alkyl side-chains exhibit dispersing behavior. Deflocculation of the resins was observed in the simulations. A critical concentration ratio for the resin and asphaltene exists. The coagulation of heavy oil occurs when the concentration ratio of resin and asphaltene is less than this critical value.

Key words: Heavy oil, Colloid, Polydispersed system, Self-association, Supermolecular structure, Aggregate structure, Dissipative particle dynamics