A new method of "geochemical logging" for studying Domanic deposits
Based on the study of the rocks of the Semiluksky horizon from the northwestern slope of the South Tatar arch (Tatarstan Republic), new data on the ratio of scattered organic matter, carbonate and siliceous components in domanicite rocks were obtained. Based on the results of geochemical studies of the bitumoids of these rocks, new information was obtained on the distribution patterns of aromatic biomarkers in rocks of various lithological composition. Peculiarities of distribution of paleonyerathan and isorenierathan in such rocks are revealed. Due to the use of aromatic biomarkers, a number of new geochemical coefficients have been developed, which make it possible to characterize not only Domanic strata along the sediment section, but also the processes of their transformation, starting from the stage of biota formation. The substantiation of the use of these geochemical coefficients when carrying out geochemical logging along the well column to establish the boundaries of the Domanic strata formation and productive intervals in them, as well as to assess the facies conditions of their formation, is given. At the same time, the patterns established by these coefficients correlate well with other geochemical and geological parameters. The studies performed have shown that at least two types of organic matter are present in the domanicite sequence: migrational, more mature and thermocatalytically transformed, and syngenetic, less mature with a low degree of thermocatalytic transformation. The application of the developed geochemical coefficients determines a new approach to the use of «geochemical logging» in the complex of express logging while drilling. When studying cuttings, these coefficients make it possible to identify reservoir intervals, zones of fracturing and decompression, containing traces of migrational hydrocarbon fluids, moved hydrocarbons, which may indicate the presence of oil deposits. The integration of geochemical studies of cuttings with its rapid study by pyrolysis and X-ray analysis methods can significantly increase the accuracy of identifying interlayers with a high content of organic matter in the section of domanicite rocks, as well as potential reservoirs with moved migrational hydrocarbons.