Effect of a Coated Wall on Wax–Asphaltene Molecule Diffusion, Aggregation, and Adhesion Mechanism: A Molecular Dynamics Simulation Study

Abstract

Coating is increasingly used as a cost-effective strategy for controlling heavy component deposition in waxy crude oil transportation flowlines. This paper systematically investigated the micro influence mechanism of the coated wall on the diffusion, aggregation, and adhesion behavior of wax–asphaltene molecules by the molecular dynamics (MD) method. A set of experiments was performed to determine the properties of the waxy crude oil. For overcoming the limitations of the model simplification of previous MD studies, the MD models based on experimental data were developed to characterize the motion behavior of wax–asphaltene molecules on non-coated and coated wall surfaces, and the simulated densities of crude oil components had an error of less than 5% with the National Institute of Standards and Technology (NIST) data, which showed that the established model was accurate and reliable. The simulation results showed that two condensate oil layers were formed on the non-coated wall surface, the diffusion and aggregation behavior of wax–asphaltene molecules were enhanced under the low-temperature condition, and there was considerably heavy component molecules adhesion to the non-coated wall surface. The analysis of mean square displacement, radial distribution function, and relative concentration distribution revealed that 288.15 K was the peak wax precipitation, which was consistent with the experimental conclusion. It was also found that the presence of low surface energy coating weakened the diffusion of heavy component molecules. The epoxy silicone-coated had the weakest interaction with wax–asphaltene molecules. Moreover, the fact that the coated wall had a certain inhibitory effect on the aggregation and adhesion of wax–asphaltene molecules in the pipeline was proven, where the epoxy silicone-coated had the strongest inhibitory effect. These investigations present new insights and guidance for controlling heavy component deposition by coating in the pipeline transportation process of waxy crude oil.