Conventional and high-field pulsed EPR experimental studies on Bazhenov oil formation under the influence of 50 Hz electromagnetic field

•EPR spectroscopy is a reliable tool for studying EM-heating effect on heavy oil EOR.•EM heating increases saturated hydrocarbons in heavy oil after 50 min exposure.•EM heating decreases resins and asphaltenes in heavy oil after 50 min exposure.•EM heating improves normal in heavy oil by alkyl substituents elimination. Heavy and extra-heavy oil are generating considerable interest in terms of replacing light oil role in the next few years. Nowadays, various enhanced oil recovery (EOR) methods are under development for an effective exploration and oil refining of unconventional oil sources. Electrical methods are among the most commonly discussed types of EOR techniques. Despite this interest, no one as far as we know has studied the effectiveness and mechanisms of electromagnetic (EM) heating influence on heavy oil conversion. It is common knowledge that heavy oils often contain stable paramagnetic centers, which potentially can serve as at least signaling species to follow the EOR upgrading degree. For the first time, to the best of our knowledge, pulsed and high-frequency (high-field, with 3.4 T detection magnetic field) electron paramagnetic resonance (EPR) techniques were exploited to investigate the EM heating influence on Bazhenov formation heavy oil by subjecting it to 50 Hz (0.75 T) electromagnetic field in laboratory conditions. The obtained samples were analyzed by a set of physico-chemical methods including SARA analysis (S: Saturates, A: Aromatics, R: Resins, A: Asphaltenes), gas chromatography–mass spectrometry (GCMS) in addition to pulsed and conventional (cw) EPR spectroscopy. SARA analysis has shown an increase in the content of asphaltenes from 1.2 ± 0.3 wt% in the initial oil to 1.4 ± 0.4, 1.4 ± 0.3, 1.3 ± 0.2, 1.3 ± 0.5 wt% in the samples obtained at 10, 20, 30 and 40 min respectively. Interestingly, this content has drastically dropped to 0.2 ± 0.05 and 0.3 ± 0.02 wt% in the samples obtained at 50 and 60 min of EM heating. Analogically for resins content change which has firstly increased from 1.5 ± 0.5 wt% in the initial oil to 1.9 ± 0.5, 2.6 ± 0.6, 3.0 ± 0.2, 3.0 ± 0.6 wt% in the samples obtained at 10, 20, 30 and 40 min respectively. Then this content has decreased to 0.5 ± 0.05 and 1.0 ± 0.04 wt% in the samples obtained at 50 and 60 min of EM heating. The content of saturated and aromatic compounds has been found to reach 99.3 ± 0.6 wt% in the sample obtained at 50 min comparing to 97.3 ± 1.1 wt% in the initial oil. Moreover, the GC