Analysis of Viscous Mechanism of Heavy Oil Based on Density Functional Theory (DFT)

Density functional theory (DFT) in quantum mechanics is widely used in the calculation of interaction energy between molecules due to its high accuracy and relatively small amount of calculation, and plays an important role in catalysis, metal coordination, supramolecular arrangement and stacking and other fields. The viscosity and flow characteristics of heavy oil are closely related to its internal composition and structure. However, the composition of heavy oil is very complex. This article focuses on the analysis of the main components and structure of heavy oil, and further studies the viscosity inducing and viscosity reducing mechanisms of heavy oil. Using the B3LYP scheme of density functional theory algorithm in quantum chemistry ab initio Gaussian-03 program ω 97 basis groups were fully optimized for the above model compounds and hydrogen bonding interaction models. Structural optimization of resin and asphaltene molecules was carried out using B3LYP/6.31G (d. p), with a minimum frequency of positive values and no imaginary frequencies, indicating that the optimized structure is stable. Through analysis, the polar group of resin and asphaltene in heavy oil is the main structure factor of viscous oil. The intermolecular van der Waals forces, π−π forces between aromatic layers, and hydrogen bonding are the main forces between heavy oil molecules. The main factors causing viscosity in heavy oil are the strong interaction force between large molecules and aggregated supermolecules, and the difficulty in thermal movement; The stacking, entanglement, interpenetration, and curling of macromolecular chains and circular molecules further increase the flow resistance, which is also an important factor in increasing the viscosity of heavy oil. Clarifying the viscous mechanism of heavy oil can lead to targeted molecular design of heavy oil viscosity reducing agents, significantly improving the viscosity reduction rate of heavy oil.