A critical review on the viscosity reduction mechanisms of magnetically-treated waxy crude oil

Objective At ambient temperatures, the poor flowability of waxy crude oils presents significant flow assurance challenges for oil production and pipeline transportation. Magnetic treatment represents a physical modification method for crude oil that is relatively easy to implement. However, the underlying mechanisms are complex, and the magnetorheological effects are not consistently correlated with factors such as the strength and duration of the magnetic field. Clearly elucidating the mechanism of magnetic treatment for waxy crude oils is therefore an essential prerequisite for advancing the research and application of this technology. Methods Through a systematic review of the existing literature, this study summarizes the viscosity-reducing characteristics of crude oil subjected to magnetic treatment. Building upon this foundation, it systematically synthesizes the current hypotheses concerning the mechanisms of viscosity reduction of magnetically treated waxy crude oil. These hypotheses are critically analyzed using established theories, including magnetorheology and the rheology of dispersed systems. Results The analysis suggests that microscopic morphological alterations of particles, such as aggregation, dispersion, or alignment induced by the magnetic field, are likely not the primary cause of the observed viscosity reduction. While wax crystals exhibit diamagnetic behavior, their low magnetic susceptibility renders the direct alteration of interparticle forces between them by the magnetic field insufficient to achieve significant viscosity reduction. The prevailing evidence indicates that the magnetic field most probably exerts its modification effect indirectly. This is achieved by influencing the state and behavior of resins and asphaltenes, which subsequently alters their interactions with the wax crystals and, ultimately, modifies the interactions between the wax crystals themselves. Conclusion Future research aimed at deepening our understanding of the magnetic modification mechanism should prioritize investigating how magnetic fields influence the inter-particle or inter-molecular forces between paraffinic constituents in crude oil.