Resin from Liaohe Heavy Oil: Molecular Structure, Aggregation Behavior, and Effect on Oil Viscosity

Resin accounts for over 30% of the composition of Liaohe heavy crude oil and can result in severe difficulties in oil recovery and transportation. To determine the structure of the resin extracted from Liaohe heavy oil, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, elemental analysis, Fourier-transform IR spectroscopy, and NMR spectroscopy were employed to determine the chemical structure of the resin. The results showed that the resin molecule is composed of anthracene, two cycloalkanes, and six alkyl chains grafted on the cyclic-structure core. UV-visible spectroscopy, turbidity measurements, dynamic light scattering, optical microscopy, and scanning electron microscopy were used to observe the resin aggregation behavior upon addition of a poor solvent. The effect of the resin on the rheology of model oils was investigated systematically. The pi-pi interactions among resin molecules impose a critical impact on the assembly of the resins. The quantum mechanics calculations revealed that there are two low-well depths of interaction energy when two resin molecules approach, which implies that the bending and branching structure of the resin aggregates may originate from the staggered stacking of the resin molecules. These findings can improve our understanding of the resin aggregation behavior and thus enlighten the solution to the flowing problem during recovery and transportation of heavy oil with a high resin content.