This paper presents the results of the conversion of high-carbon Domanic rock from sediments of the Semiluki-Mendym horizon of the Volga-Ural petroleum Basin in sub-and supercritical waters at temperatures of 320, 374, and 420 °C in a neutral nitrogen environment for 1 h. The initial sample is a siliceous-clay carbonate rock with an organic matter content of 10.6 wt %, the largest part of which is insoluble kerogen. The end products of all experiments are characterized by an increase in the content of saturated hydrocarbons with a noticeable decrease in the content of resins and asphaltenes. The highest yield of the extract (3.98 against 3.12 wt %) compared with the initial rock is observed in the experiment in subcritical water at 320 °C as a result of the preferred degradation of resins and more complete extraction of asphaltenes from the rock. With an increase in temperature to supercritical water conditions at 374 °C and pressure up to 24.6 MPa, kerogen transformation processes are observed due to the C−C, C−N, and C−O bonds destruction with the formation of low-boiling saturated hydrocarbons and high-carbon components such as carbene−carboids in the products of the experiments. The highest yield of saturated hydrocarbons occurs at the experiment of Domanic rock in supercritical water at 420 °C and 24.4 MPa. Under these conditions, in comparison with lower temperatures, the yield of the extract from the rock decreases due to intense gas formation. In the composition of the gases formed in the experiments, there are hydrocarbons: CH 4 , C 2 H 6 , C 3 H 8 , and i-C 4 H 10 , indicating the destruction of C−C bonds. Dehydrogenation processes in supercritical water at 420 °C are noted by the presence of H 2 in the reaction system. Structural and phase changes in the mineral composition of Domanic rock were discovered as a result of supercritical water exposure at 374 and 420 °C. In particular, the structure of mica was changed due to the isolation of a separate phase of montmorillonite from it.

The aquathermolysis process is widely considered to be one of the most promising approaches of in-situ upgrading of heavy oil. It is well known that introduction of metal ions speeds up the aquathermolysis reactions. There are several types of catalysts such as dispersed (heterogeneous), water-soluble and oil soluble catalysts, among which oil-soluble catalysts are attracting considerable interest in terms of efficiency and industrial scale implementation. However, the rock minerals of reservoir rocks behave like catalysts; their influence is small in contrast to the introduced metal ions. It is believed that catalytic aquathermolysis process initiates with the destruction of C-S bonds, which are very heat-sensitive and behave like a trigger for the following reactions such as ring opening, hydrogenation, reforming, water–gas shift and desulfurization reactions. Hence, the asphaltenes are hydrocracked and the viscosity of heavy oil is reduced significantly. Application of different hydrogen donors in combination with catalysts (catalytic complexes) provides a synergetic effect on viscosity reduction. The use of catalytic complexes in pilot and field tests showed the heavy oil viscosity reduction, increase in the content of light hydrocarbons and decrease in heavy fractions, as well as sulfur content. Hence, the catalytic aquathermolysis process as a distinct process can be applied as a successful method to enhance oil recovery. The objective of this study is to review all previously published lab scale and pilot experimental data, various reaction schemes and field observations on the in-situ catalytic aquathermolysis process.

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