An objective look at the geological structure of deposits with hard-to-recover hydrocarbon reserves

The article is devoted to the actual problem of long-term studies of the geological structure of deposits with hard-to-recover hydrocarbon reserves. The evolution of views and the results of studies of the geological structure of oil and gas deposits in various periods of exploration and evaluation work in the West Siberian oil and gas province are described in detail. Possible versions of models of complex structures of hard-to-recover reserves of the Achimov stratum and the Neocomian complex are considered. Various geological, technological, and economic criteria for classifying hydrocarbon reserves as hard-to-recover are presented, and options for classifying development objects based on high water cut of well production are illustrated. An attempt is made to justify the principle of classifying these reserves as unprofitable hard-to-recover reserves. As a result of a detailed study of the geological structure of a number of fields in Western Siberia, mainly taking into account production wells, the features of the Jurassic and Cretaceous deposits and their lower sections, the Achimov formation, were established, including in connection with the features of the previously formed anomalous sections of the Bazhenov formation. An analysis of the changes in the thickness of the Achimov formation by field indicates that the total thickness of the Bazhenov formation and its anomalous section are compensated by an increase in the thickness of the Achimov formation. A detailed correlation has revealed that adjacent blocks are alternately subducted along con-sedimentary faults, and positive structures are gradually flattened, suggesting that the Achimov formation is compensatory.