This paper discusses the results of the influences of subcritical (T = 320 °C; P = 17 MPa) and supercritical water (T = 374 °C; P = 24.6 MPa) on the yield and composition of oil hydrocarbons generated from carbonaceous–siliceous Domanic shale rocks with total organic content (C_org) of 7.07%. It was revealed that the treatment of the given shale rock in sub- and supercritical water environments resulted in the decrease of oil content due to the intensive gas formation. The content of light hydrocarbon fractions (saturated and aromatic hydrocarbons) increased at 320 °C from 33.98 to 39.63%, while at 374 °C to 48.24%. Moreover, the content of resins decreased by almost twice. Insoluble coke-like compounds such as carbene–carboids were formed due to decomposition of kerogen after supercritical water treatment. Analysis of oil hydrocarbons with FTIR method revealed a significant number of oxygen-containing compounds, which are the hydrogenolysis products of structural fragments formed after destruction of kerogen and high-molecular components of oil. The gas chromatography–mass spectroscopy (GC–MS) method was applied to present the changes in the composition of mono- and dibenzothiophenes, which indicate conversion of heavy components into lighter aromatic hydrocarbons. The specific features of transforming trace elements in rock samples, asphaltenes, and carbene–carboids were observed by using the isotopic mass-spectrometry method.

The transformation of the organic matter (OM) of low-permeable carbon-rich domanik rock of the Romashkino oilfield in sub- and supercritical water (SCW) at temperatures of 320, 374, and 420°C and pressures of 17, 24.6, and 24.4 MPa in a neutral medium has been studied. The original rock with a TOC content of 7% has a high oil generation potential and a low productivity index. The productivity index increases with an increase in the severity of the thermal treatment of the rock, which is due to intense kerogen degradation resulting in the formation of free hydrocarbons that are easy to recover from the rock. In rock extracts, in comparison with the original rock, the amount of saturated and aromatic hydrocarbons increases by more than two times and that of resin–asphaltene substances decreases. Distinctive features of the yields and compositions of rock extracts depending on the temperature of the experiments have been revealed. The highest yield of the extract was observed in the experiment with subcritical water at 320°C and associated with the degradation of resins and more complete extraction of asphaltenes and high-molecular-weight n-alkanes from the rock. Treatment in SCW at 374 and 420°C leads to intensive degradation of the kerogen structure involving the detachment of aliphatic chains from large fragments of kerogen and asphaltene macromolecules to form lower n-alkanes and carbon-rich substances, such as carbenes and carboids. The structure of asphaltenes becomes more condensed and oxidized in the SCW medium at 420°С, leading to a decrease in their paramagnetic properties. Using the EPR technique, the features of hyperfine splitting of the vanadyl complex line on ¹⁴N nitrogen nuclei have been revealed in the spectrum of asphaltenes of the SCW experiment at 420°С, indicating specific changes in their structure.

The effect of 1-propanol on the transformation of the organic matter (OM) of the domanik rock of the Romashkino field with the С_оrg content of 7.26% in supercritical water (SCW) at 374°С was studied. The OM undergoes essential changes in the course of these experiments. According to the Rock-Eval data, addition of 1-propanol to the SCW reaction medium increases the rock production index (PI) by a factor of almost 2, from 0.48 to 0.76, owing to high degree of degradation of the insoluble kerogen, from 22.17 to 0.30 mg g^–1 rock (parameter S₂). A part of kerogen degradation fragments transforms into resins and aromatic compounds whose content in the extract increases by a factor of more than 2, whereas the content of saturated hydrocarbons (HCs) considerably decreases. As compared to the experiment in straight SCW, insoluble high-carbon substances of carbene/carboid type are absent. The gas phase contains 78.8 rel % СО₂, which favors the recovery of high-molecular-mass oil components from the low-permeability domanik rock. The formation of HC gases is indicative of the occurrence of intense degradation processes involving homolytic cleavage of C–C bonds by the radical-chain mechanism. The content of high-molecular-mass n-alkanes C₁₇–C₂₇, phenanthrenes, and dibenzothiophenes in the transformed shale oil increases. The structure of aromatic HCs, resins, and asphaltenes after treatment in SCW with the addition of 1-propanol becomes more condensed, and the content of aliphatic fragments and sulfoxide S=O groups decreases, suggesting the occurrence of dehydrogenation with the elimination of long alkyl chains via cleavage of heteroatomic bonds. In the process, 1-propanol not only acts as a cosolvent but also prevents the recombination of radicals formed in the course of kerogen degradation, which is confirmed by a decrease in the concentration of free radicals in resins and asphaltenes. The structurization of resins and asphaltenes leads to the removal of metals from porphyrin molecules and to a decrease in the paramagnetic properties. After the treatment both with SCW and with SCW + 1-propanol, the resins are characterized by superhyperfine splitting of the line of the vanadyl complex, caused by interaction with the ¹⁴N nuclei, which suggests transformations of alkylporphyrins into monocycloalkylporphyrins via dealkylation, demetalation, and hydrogenation. After the autoclave experiments, the structure of mica in the mineral matter of the domanike rock undergoes changes due to segregation of the separate montmorillonite phase.