Significant reduction of the viscosity of waxy model oils by DC electric field

Abstract

Wax crystallization at low temperatures greatly increases the viscosity of waxy oils and poses flow assurance challenges to their pipeline transportation. The conventional methods of lowering the viscosity of waxy oils, such as adding chemicals or externally heating the pipeline, are carbon-intensive and sometimes ineffective. Electrical treatment has emerged as a promising and low-carbon method to improve the cold flowability of waxy crude oils. While previous studies primarily focused on crude oil systems and highlighted the critical role of charged particles such as resins and asphaltenes in electrical treatment, this study systematically investigated the electrorheological behavior of model waxy oils composed solely of mineral oil and paraffin wax, without such charged particles. Using a rheometer equipped with an Electro-Rheology accessory, we characterized the changes in the oil's viscosity under DC electrical fields ranging from 0 to ±3 kV/mm. Significant viscosity reductions of up to 89 % were achieved. The viscosity reduction also strongly depended on the field direction, and negative electric fields generally result in higher reduction than those achieved by positive electric fields under the same field strength. Direct visualization by a high-resolution camera indicated that the migration of wax crystals toward electrodes is mainly responsible for the observed viscosity reduction, providing direct experimental evidence of the mechanisms supporting the negative electrorheology of waxy oils. This research greatly advances the mechanistic understanding of the interactions between wax crystals and electric fields, expanding the potential application of electrical treatments for flow assurance in pipelines.