In this study, the specific features of Ashal'cha heavy oil conversion were revealed. The hydrothermal catalytic experiments were carried out in a CO2 environment and in the presence of oil-soluble carboxylate metals such as Fe, Co, and Cu at the temperature of 300 degrees C. The results have shown that the catalyst and minerals of reservoir rocks have significant impact on the transformation behavior of group, structural group, and hydrocarbon compositions of oil. The most significant changes in the composition of heavy oil were established after hydrothermal treatment in the presence of a rock-forming additive, clay mineral (kaolin), which are reflected in a significant increase in the content of saturated and aromatic hydrocarbons and a decrease in the content of resins and asphaltenes. Furthermore, the changes in the structure of asphaltenes led to the increase of aromaticity and oxidation degrees. It was found that the catalyst metals mainly concentrate on the asphaltene structures and on the rock-forming reservoir minerals. It has been shown that the concentration of Fe increases up to 5.84% and that of Cu from 0 to 0.25% after catalytic treatment of oil with kaolin. A similar change was observed in the asphaltene content of rock extracts where Fe and Cu concentrations reach 1.38 and 0.31%, respectively, with no Co presence in asphaltene content. The number of catalytically active metals such as Ti, Fe, Cr, Mn, Co, Ni, Cu, Zr, and Ba was found in the rock obtained after the experiment and the extraction of organic matter. Moreover, a slight decrease from 2.27 to 1.93% in Fe concentration included in the catalytic complex has been established with an increase in Co and Cu concentrations, which were practically absent in the original rock, to 0.036 and 0.038%, respectively. It has been established as well that the studied metal complexes (Fe, Co, and Cu) with carboxylate ligands can penetrate not only into the pore space of the rock but also into asphaltenes, thereby allowing them to catalyze the process of heavy oil upgrading under hydrothermal conditions.