Microscopic Mechanism of Wax Precipitation and Gelation of Waxy Crude Oil Based on Molecular Dynamics Simulation

• Molecular dynamics model links cooling-driven van der Waals dominance to gelation phase transition. • Wax-wax attraction drives gelation, aligning with macro-rheological trends.. • RDF peaks rise, Rg drops, chains coil near gelation, indicating phase transition.. • Self-diffusion predicts wax points within 6-11% error, validating simulations. To reveal the microscopic mechanism of wax precipitation and gelation in waxy crude oil systems at the molecular level, this study constructs a simulated waxy crude oil system based on the physical property parameters obtained from macroscopic experiments and conducts molecular dynamics simulations using Materials Studio software.The results show that during the cooling-induced wax precipitation and gelation process, the kinetic energy of the system decreases while the van der Waals interaction energy increases. The increase in the radial distribution function peaks indicates enhanced molecular aggregation ordering. Meanwhile, the decrease in the radius of gyration suggests a conformational transition of molecular chains from an extended to a coiled state. Both changes exhibit significant variations near the gelation temperature. Analysis of the cohesive energy density and intermolecular interactions in the crude oil system reveals that the interactions between wax molecules play a dominant role in the gelation process. By examining the changes in the self-diffusion coefficient of wax molecules, the characteristic temperatures of wax precipitation of the oil sample were determined and compared with experimental measurements. The relative errors for the wax appearance temperature (WAT) and peak wax precipitation temperature (WPT) were less than 6% and 11%, respectively, demonstrating the reliability of this method. This study elucidates the microscopic mechanism of wax precipitation and gelation in waxy crude oil at the molecular level, providing a theoretical foundation at the molecular scale for optimizing crude oil modification processes and enhancing pipeline transportation efficiency.