Precambrian rocks are widespread within all continents of the Earth; that said, sedimentary associations of these deposits are of special interest in search for oil and gas fields. A wide range of paleontological, lithological and geochemical methods is utilized for conducting integrated geological-geochemical analysis and evaluating the initial hydrocarbon generating potential of organic matter of Precambrian source rocks. Investigated were peculiarities of depositional environments of the organic matter, specific features of its composition in sedimentary rocks and its generation characteristics. Own research efforts were performed in combination with generalization of other authors’ publications focused on Precambrian sequences enriched in organic matter – their occurrence, isotopic and biomarker characteristics and realization schemes of the hydrocarbon generation potential of Precambrian organic matter in the process of catagenesis. Geochemical peculiarities of initial organic matter are illustrated on various examples, type of the organic matter is determined together with the character of evolution of realization of its initial generation potential.
Consideration is given to results of geochemical analysis of organic matter and oils of the Proterozoic (the RF-V complex) and the Paleozoic (the pay intervals D2, D3, C1-2) of the eastern part of the Volga-Urals petroleum basin. The obtained data is corroborated by results of 2D basin modeling along four regional profiles two of which are situated in the Kama and two in the Belaya parts of the Kama-Belaya aulacogen. An update is given to earlier data on degree of catagenetic alteration of oil/gas source rocks of the Riphean-Vendian play, maps of catagenesis are constructed. New evidence is provided concerning presence of Precambrian oils in the Paleozoic plays. The oils under investigation are mixed – those formed from generation products of the Precambrian (Riphean, Vendian) and Paleozoic (Devonian and Early Carboniferous) source rock intervals. The results of modeling have shown that the principal source rock intervals in the RF-V play of the Kama part of the Kama-Belaya aulacogen are deposits of the Kaltasy formation of the Lower Riphean and the Vereshchagino formation of the Upper Vendian, while in the Belaya part these are rocks of the Kaltasy, Kabakov, Olkhovo, Priyutovo, Shikhan and Leuza formations of the Riphean and the Staropetrovo formation of the Vendian. It is found that the interval of the main oil and gas window increases in the southeastward direction. In both depressions of the Kama-Belaya aulacogen, a single oil play is distinguished that functions within the stratigraphic interval from the Riphean to the Lower Carboniferous. As the principal petroleum source rock intervals within this play, Riphean-Vendian deposits are considered, reservoirs are confined to the Riphean carbonate complex, Upper Vendian and Middle Devonian clastic deposits, while the Upper Devonian – Tournaisian deposits serve as the upper seal.
