This paper is devoted to solution of problems connected with forming deposits of heavy oils and natural bitumens in Permian sedimentations on the territory of Tatarstan and to questions of prognostic evaluation of their technological properties in relation to degree of their natural transformations. Comparative investigation of composition and properties of their various representatives (heavy oils, malts, asphalts and asphaltites) occurring on drill log and proved area of Permian producing deposits on the territory of m Tatarstan in depth interval from 1 to 349 m was carried out, in connection with solution of problems on preparation of natural bitumen fields to development. The systematization of studied samples recovered by both natural inflow from wells and their extraction from bitumen saturated rocks of various age and mineralogical composition by oil-bitumen-bearing complexes, and within the last ones, by relation to local erosion basis, allowed to reason that characteristic changes in the composition bitumens leading to formation of their various chemical types are determined mainly by biodegradation process presenting practically in all oil-bitumen-bearing complexes and, especially, enhancing in carbonate reservoirs and horizons consisting of fragmental terrigenous sedimentary rocks undergone the washout and inluence of external factors.

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It was shown that biodegradation processes leading to absence of light hydrocarbon fractions in their composition, including normal and isoprenoid alkanes, and predominance of resin- asphalt compounds enriched by hydroxyl and ester oxygen, along with sulfur and nitrogen atoms, determine technological properties of natural bitumens during their recovery and processing.

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