Advance in investigation on mechanism of electric field treatment for improving the cold flowability of crude oil and its prospect

High-voltage electric field treatment is an emerging approach to improve the cold flowability of crude oil, of which the physical principle is the negative electrorheological effect of crude oil other than electric heating and electric field dehydration. Based on the review of literatures on electrorheology, several mechanisms of negative electrorheological effect were summarized, and the problems in the electric field treatment mechanisms of crude oil, such as particle aggregation into chains, increasing the particle size of wax crystal, and enhancing the polydispersity, were analyzed. Besides, the basis of wax particle interface polarization was explained. Generally, the co-existence of wax particles, resins and asphaltenes is the necessary condition to realize the treatment effect of electric field. When a high-voltage electric field is applied, the charged particles(i.e. the resins and asphaltenes) in the crude oil would aggregate on the surface of wax crystal, which is the interface polarization. During the process, the electrostatic repulsion between wax particles is increased while their attraction is weakened, resulting in improved cold flowability of the crude oil. Therefore, the behavior of resins and asphaltenes in the oil is the key to understand the mechanism of the negative electrorheological effect of crude oil, which mainly includes three processes: the migration of resins and asphaltenes from the bulk phase to wax particles upon the application of electric field,accumulation of resins and asphaltenes on the surface of wax particles, and their diffusion back to the bulk phase after the removal of electric field. In the future, further in-depth and quantitative research should be focused on these three processes to fully reveal the scientific mechanism of the electrorheological effect of crude oil.