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Rimma Gottikh, VNIIGeosistem (Russian Federation)
Renat Muslimov, Kazan State University (Russian Federation)
Bogdan Pisotskiy, Institut of Problem Of Oil and Gas (Russian Federation)
Irina Plotnikova, Kazan State University (Russian Federation)
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Geodynamic processes have produced numerous dislocations in the crystalline basement of Volgo-Kama anticline, which have been revealed by the exploratory drilling. Fractured zones with the varying thickness, decompression degree and fluid content have been recorded by a great number of wells that penetrated the crystalline basement. The deep well Novoelkhovo-20009 can serve as the best example. The Corg content of the crystalline basement in most samples is 0.01 to 0.09 percent of the rock mass, in some individual cases reaching 0.15 to 0.5 percent. The content of chloroform bitumens does not generally exceed 0.0003 to 0.008 percent, rarely reaching 0.01 to 0.02 of the rock mass. Their highest concentrations are recorded in the most fractured zones. Their group composition is dominated by resins and includes minor amounts of asphaltenes. The fraction composition of hydrocarbons in them is very diverse. Some samples include a wide range of hydrocarbons from Ñ9 to Ñ33, while others contain narrower fractions with different final boiling points. The permeable intervals of the basement contain a wider range of hydrocarbons. Compositionally similar bitumens may occur at different depths but their fractional and group compositions have been found to depend on the sorption and filtration properties of rocks. The following features have been detected by IR spectra: ÑÍ2 groups, ÑÍ3 of paraffin structures, ÑÍ2 groups of paraffin chains, aliphatic ethers, C-C aromatic ring groups and C-O links. The composition and distribution pattern of polycyclic aromatic hydrocarbons (PAH) contained in bitumens of the crystalline basement have been studied using a spectrofluorometer. The total amount of the identified PAHs ranges from several tens to 430 ng/g and their contents increase in fractured, cataclastic granitoids. Thus, the gas and liquid hydrocarbon components occur in the crystalline basement rocks of the studied regions, penetrated to a depth of more than 3000 m, due to the impact of the compound reduced fluid systems, sealed within the secondary inclusions in rocks and minerals, on ancient rock complexes. The crystalline basement studies have revealed how the deep, hydrogen-hydrocarbon degassing is displayed today. It has also been shown that the total amount of hydrocarbons produced in the Romashkino field have already significantly exceeded its expected reserves. Moreover, it is obvious that the volume of the extracted oil could not have been produced by the Domanic beds of the South Tatarstan Arch, conventionally believed to be a major source for the STA's oil field. At the same time, independent oil-field geochemical studies have revealed twelve characteristics of a possible upward oil flow into the sedimentary cover.
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