Hard-to-recover reserves include objects with low permeability, with ultra-high viscosity of oil, as well as hydrocarbon reserves in oil source bed, such as Bazhenov formation in Western Siberia, in Domanic type deposits in the Volga-Ural and Timan-Pechora oil and gas province, Khadum horizon in Pre-Caucasian region, etc. The hard-to-recoverability of deposits is shown on the example of the Bazhenov formation of Western Siberia. Original methodological techniques for studying seabed sediments at various levels are resented. Special attention is paid to the proof of the generation potential of oil-producing formations in the section on the basis of complex geological, petrophysical, and geochemical research methods. It is shown that when studying oil source bed represented by kerogen-carbonate-clay-siliceous rocks with a variable content of components, it is fundamental to study the lithological characteristics of the rocks and the most important rock-forming component - solid organic matter (kerogen) and its derivatives (hydrocarbons). It is interesting to realize that certain dependence between the established categenetic maturity of kerogen defines the value of the initial reservoir pressure. Based on analysis of the results of Bazhenov formation exploitation, characterized by dispersion between the initial reservoir pressure and saturation pressure, the autors show how this dispersion affects on the exploitation indicators depending on the growth of the gas factor compared to the initial gas content, an increase in oil viscosity, decrease in permeability, etc. It is noted that in the conditions of exploitation without maintaining reservoir pressure, the method of «production drop curves» appears to be the most effective calculating remaining recoverable oil reserves.
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