Rheological implications of the inclusion of ferrofluids and the presence of uniform magnetic field on heavy and extra-heavy crude oils

Abstract

This study embraces the evaluation of the rheological and magneto-rheological properties of heavy and extra-heavy crude oils by applying nanotechnology and magnetism as technological solutions in reducing viscosity. Mixtures of heavy oils with ferrofluids were used to study the viscous effects induced by the action of external magnetic fields. The rheological evaluation covered rotational and oscillatory tests as a function of time and temperature. In the magneto-rheological characterization, there were analyzed the magnetoviscous effects. The results revealed that the crude oils are viscoelastic materials that follow the Generalized Maxwell Model over a wide range of temperatures (-5 to 60 °C). It was also proved that the synergy between the carrier liquid and the nanoparticles promoted a significant reduction of viscosity (~98–99%) and viscoelasticity, which was directly related to the simultaneous action of the solvent and the asphaltene adsorption onto the nanoparticles surface. Critical concentrations of nanoparticles (0.2 wt% and 0.6 wt%) were proved to promote the maximum decrease in viscosity (additional ~ 0.3–0.5% or 1000-3000 cP) and the elastic storage modulus, which was crucial evidence of their effect on hindering the aggregation mechanisms of asphaltenes. In the heavy oil–ferrofluid mixtures, a magneto-rheological effect was demonstrated. The magnetic field attenuated the initial relaxation processes, leading to an increase in the viscosity and shear stress. The phenomenon was attributed to the formation of magnetic chains, such as that observed in magneto-rheological fluids. These results were supported by Scanning Electron Microscopy, which showed the formation of magnetic-field induced thick columnar assemblies of nanoparticles-asphaltene complexes.