Abstract <p>Hydrothermal superimposed processes in sedimentary complexes are a well-known process. They manifest themselves in changes of rock composition (both mineral and organic) and their structural characteristics. From the point of view of the rock properties as elements of oil and gas-bearing complexes, this means a possible change in oil and gas generating and reservoir properties, as well as a change in the phase composition of hydrocarbons. In oil and gas geology hydrothermal processes began to be taken into account relatively recently, when their role in the formation of the properties of reservoirs and oil and gas source rocks became obvious. Secondary superimposed carbonatization is considered as the most widespread process and its hydrothermal nature is substantiated.</p>