The mechanism of viscosity reduction of waxy oils induced by the electric field: A correlation between the viscosity reduction and the charged particle accumulation on wax particles.

Wax molecules crystallize at ambient temperature, causing the crude oil to become a dispersed system, which poses challenges in the flow assurance of pipelines. Improving the cold flowability of crude oil is the fundamental solution to tackle these problems. Applying an electric field to waxy oil may markedly improve its cold flowability. The adhesion of charged particles on wax particles' surface under the electric field has been demonstrated as the essential mechanism of the electrorheological effect. However, the correlation between the accumulated charged particles and the induced viscosity reduction has not been explored quantitatively. In this study, the viscosity and impedance of four crude oils before and after electric treatment were measured. The conductivity changes of the oils' continuous phase were obtained by an equivalent circuit model. And then, the charged particles' concentration before and after electric treatment was calculated by the Stokes equation. The results showed there is a positive correlation between viscosity reduction and charged particle concentration reduction in the continuous phase. Importantly, this correlation is also quantitatively applicable to the results of ten different waxy oils which has been published. This study provides a quantitative basis for the mechanism of electrorheological behavior of waxy oils.