The article discusses the theoretical prerequisites for the formation of hydrocarbon fields at great (more than 6 km) depths from the point of view of the possibility of generation processes, their features, boundary conditions for the preservation of accumulations and the direction of fluid transformation under the influence of high temperatures and pressures, as well as changes in the reservoir filtration properties of reservoirs and seals. Until recently, at the axiom level, there was an idea that the distribution of oil accumulations is limited to a depth of 4-5 km, while the possibility of the existence of gas and condensate accumulations at great depths was not in doubt. Such zoning of hydrocarbons accumulations was the basic one in the sedimentary migration theory. However, large-scale drilling of wells to ultra-deep horizons and the discovery of oil accumulations in them forced us to reconsider these views and look for an explanation for this phenomenon. The article focuses on the possibility of the formation of liquid hydrocarbons accumulations based on the analysis of hydrocarbon systems, the relationship and functioning of their individual elements in extreme conditions. The study of the features of the realization of generation potential of specific source rocks with a high (15% or more) initial content of organic matter, which accumulated in relatively deep-water conditions, showed that intensive processes of oil generation in them are directly related to the formation of microcracks at high temperatures and pressures. The article is based on the summarization of a large number of published data on the results of drilling deep wells onshore in China and the Caspian Basin, as well as on the shelf of the Gulf of Mexico and in Norway. Some geological criteria favorable for the formation of oil and gas potential at great depths have been determined.
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