Investigation of the Naturally Occurring Magnetic Nanoparticles in Crude Oil by AC Magnetic Susceptibility Experiment

The magnetic properties of oil constituents appear to be related to their key physical and chemical properties; therefore, the application of new magnetic characterization techniques for oils can make additional contributions to the field. In this study, despite the high dilution of 3d-like ions in crude oil, magnetic susceptibility measurements, recorded at different temperatures and frequencies, and electronic paramagnetic resonance measurements below room temperature were applied to detection of magnetic nanoparticles naturally found in distinctive dehydrated crude oils from the same geological reservoir, but from different oil wells. Electronic paramagnetic resonance measurements probed the presence of Fe 3+ ions, with characteristics attributed to magnetite or maghemite (γ-Fe 2 O 3 ) magnetic nanoparticles in super paramagnetic regime, whilst the presence of a magnetic susceptibility peak, that is visible only at 5000 Hz, has indicated a magnetically blocked regime, via Brownian relaxation, of iron-oxide magnetic nanoparticles. The magnetic susceptibility data showed that it is possible to distinguish the particle size distribution homogeneity and, with the support of the electron paramagnetic resonance technique, the relative fractions of iron-oxide magnetic nanoparticles in crude oils. Thus, these findings show that the magnetic susceptibility technique, supported by electronic paramagnetic resonance spectroscopy, can be applied for the study of magnetic nanoparticles in crude oils and can aid in determining and understanding the fundamental properties of crude oils. Graphical abstract