Effect of magnetic field on the apparent viscosity of water-in-oil waxy crude oil emulsion

•Viscosity reduction effect is more obvious for emulsions with higher water cuts.•Treatment time and field frequency have weak effects on the emulsion viscosity.•Field intensity and treatment temperature significantly affect emulsion viscosity.•Magnetic field causes asphaltene molecules to oscillate at the oil–water interface.•Magnetic field induces water droplet aggregation in the water-in-oil emulsion. The application of the magnetic field to reduce the apparent viscosity of water-in-oil waxy crude oil emulsions holds significant potential. A novel integrated magnetic processing apparatus was developed. The effects of magnetic treatment conditions on the viscosity of waxy crude oil and water-in-oil waxy crude oil emulsions with different water cuts were experimentally investigated. The viscosity reduction induced by the magnetic field was more pronounced for the emulsion with a higher water cut. The viscosity reduction degree of the emulsion first increased and then decreased with the increase in magnetic field intensity and magnetic treatment temperature. The viscosity reduction degree of the emulsion had a slight correlation with the magnetic treatment time and magnetic field frequency. Microscopic observation demonstrated that water droplet aggregation occurred in the magnetically treated emulsion compared to the untreated emulsion. Mechanism analysis shows that the oscillation of asphaltene molecules at the oil–water interface, the orientational arrangement of asphaltene molecules in crude oil, and the generation of monomeric water molecules induced by magnetic field contribute to the reduction in the apparent viscosity of waxy crude oil and the aggregation of water droplets. The viscosity of the emulsion is thus decreased. The research results provide a theoretical basis for the field application of viscosity reduction for water-in-oil waxy crude oil emulsion by magnetic treatment technology.