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Nowadays, there is a significant increase in the share of unconventional oil reserves such as heavy and extra-heavy oils as well as natural bitumen among the total balance of extracted petroleum feedstock. In this regard, one of the most important problems is to ensure their rational production and processing and satisfaction of the increasing consumption of energy resources. This paper investigates the effect of various solvents on the upgrading of heavy oil from the Ashalcha field under thermal steam injection by means of aromatic and industrial solvents. The results suggest that the largest amount of gases is released when benzene is added to the oil from aromatic solvents (500 g/t of oil). The results of viscosity dependence on temperature and component composition showed that oil has the lowest viscosity with the addition of toluene compared to the viscosity of the original oil and the control experiment samples, whose viscosities decrease by 4 and 3.5 times, respectively, at 10 °C. The changes in the chemical group composition, especially the significant decrease of resin content in the presence of all solvents (toluene, benzene, their mixture 1:1, as well as Solvesso-150), are explained by the destruction of associated complexes of resin molecules, thereby affecting a decrease in oil viscosity. The calculation of the indices of colloidal instability showed that the control experiment oil has the lowest stability due to the high value of CII. IR spectral data have established that a significant difference between spectra of all oils is the absence of absorption bands at 1710 cm −1 , which corresponds to the vibrations of CO carbonyl groups. The use of solvents for thermal steam exposure helps to ensure a high level of energy efficiency during the application of thermal steam exposure to heavy oil and natural bitumen deposits.

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The aim of this work was to study the fractional composition of super-viscous oil resins from the Ashalcha field, as well as the catalytic aquathermolysis product in the presence of a cobalt-containing catalyst precursor and a hydrogen donor. The study was conducted at various durations of thermal steam exposure. In this regard, the work enabled the identification of the distribution of resin fractions. These fractions, obtained by liquid adsorption chromatography, were extracted with individual solvents and their binary mixtures in various ratios. The results of MALDI spectroscopy revealed a decrease in the molecular mass of all resin fractions after catalytic treatment, mainly with a hydrogen donor. However, the elemental analysis data indicated a decrease in the H/C ratio for resin fractions as a result of removing alkyl substituents in resins and asphaltenes. Moreover, the data of 1H NMR spectroscopy of resin fractions indicated an increase in the aliphatic hydrogen index during catalytic aquathermolysis at the high molecular parts of the resins R3 and R4. Finally, a structural group analysis was carried out in this study, and hypothetical structures of the initial oil resin molecules and aquathermolysis products were constructed as well.

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