The article considers oil reserves conversion and analysis of the change reasons. Reserves listed in the State Budget of the Russian Federation and reserves according to the modern concept at the present exploration degree are analyzed. On the examples of the Volga-Urals and Khanty-Mansiysk autonomous district the methods for analyzing the formalized characteristics of deposits structure complexity are given as indicators of reserves conversion over time. These indicators should be taken into account when planning follow-up fields exploration. The numerical characteristics associated with the structural factor and lithological-physical properties are discussed. The analysis of the results showed that in the early stages of deposits exploration there is a significant need for accurate characteristics of seismic data and structural maps. Further drilling of deposits proves that the absence of such characteristics when mapping deposits of small height subsequently leads to significant changes in reserves. The presence of error maps for the geometrization of structural surfaces for different calculations would make it possible to optimally estimate the volume of an oil-saturated reservoir and categorize reserves. Discontinuous formations also make a large contribution to reserves estimation errors. As a criterion for the significance of lithological variability in the change in reserves, the reservoir boundary density parameter is used, that is, the ratio of the perimeter of all reservoir-non-reservoir boundaries within the deposit to the area. It shown that, despite the long history of studying and developing hydrocarbon deposits, it is almost always possible, using certain methods of numerically formalized methods of analysis, to obtain a rationale for identifying underexplored reserves or new understanding of the reserves structure and a quality assessment of different structural elements.
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