Objective At ambient temperatures, waxy crude oil experiences a significant decline in fluidity due to the precipitation of wax crystals that form a three-dimensional network structure, posing major flow assurance challenges for oil production and pipeline transportation. Magnetic treatment, a physical modification method, can reduce viscosity and improve low-temperature fluidity of waxy crude oil. While this method is easy to implement, its underlying mechanism is complex, and the viscosity reduction effect varies non-monotonically with factors such as the magnetic field intensity and action time. Therefore, clearly understanding the mechanism of magnetic treatment is essential to advance its research and application.

Methods The viscosity-reducing effects of magnetic treatment on crude oil were summarized through a systematic literature review. Existing hypotheses regarding the mechanisms of viscosity reduction in magnetically-treated waxy crude oil were collated, drawing on theories such as magnetorheology and dispersion system rheology. Hypotheses involving magnetic-induced particle aggregation, dispersion, alignment, and changes in intermolecular forces were analyzed to evaluate their scientific validity and rationality.

Results Changes in the microscopic morphology of particles—such as aggregation, dispersion, or alignment—under a magnetic field are unlikely to be the primary driver of viscosity reduction. This is partly because the concentration of wax crystals in liquid waxy crude oil is typically low (＜ 3％), limiting the influence of crystal size variation on viscosity. Additionally, experimental results indicate that wax crystal size may increase or decrease after magnetic treatment, yet viscosity reduction is observed in both scenarios. Although wax crystals are diamagnetic, their low magnetic susceptibility means the force generated under conventional magnetic fields is much weaker than van der Waals forces and insufficient to directly alter interactions between wax crystals. It is most likely that the magnetic field influences the dispersion of resins and asphaltenes, indirectly affecting their interaction with wax crystals and the growth process of wax crystals, thereby producing the viscosity reduction effect.

Conclusion Future research should employ techniques like Zeta potential and small-angle X-ray scattering to directly characterize wax crystal surface adsorption. Studies on alternating magnetic fields, the anomalous viscosity increase under magnetic field action, and the stability of viscosity reduction under shear-temperature coupled fields should be intensified. Additionally, multi-scale simulation methods should be developed to investigate how magnetic fields affect inter-particle and intermolecular forces among paraffinic constituents in crude oil.