M.Yu. Zubkov
 
Reservoir types in the Bazhenov-Abalak series of Western Siberia and their genesis
DOI 10.31087/0016-7894-2019-4-59-78

Using the results of detailed lithological and petrophysical studies, the main types of reservoir rocks that compose the Bazhenov-Abalak series of Western Siberia have been identified. The reconstruction of the mechanism of their formation was conducted. It has been established that secondary reservoirs formed in siliceous and carbonate varieties of rocks, as well as in their transitional siliceous-carbonate varieties, are prevailing. Less common are the so-called hydrothermal silicites formed in carbonate-siliceous types of rocks, pseudogranular reservoirs — in phosphate and carbonate coprolites, an also in ichthyodetrite-and pyrite-rich rocks. It is proved that the reservoirs present in the Bazheno-Abalak series are in most cases secondary and are formed as a result of the tectonic-hydrothermal processes impact on the Upper Jurassic deposits. The following types of reservoir rocks have been identified: fractured, fractured-vuggy, pseudogranular, pseudogranular-micro-vuggy and porous-microvuggy. Unfortunately, the origin of microcracking in various types of rocks is not always clear: either it originated in reservoir conditions under the action of tectonic stresses, or was formed in surface conditions as a result of removal of lithostatic load from samples. It is assumed that the cause of tectono-hydrothermal processes is ascending of magmatic bodies from asthenosphere, which first create stresses in the earth's crust and then in the sedimentary sequence; as a result, they split up — sub-vertical high-permeable zones of fracture dislocations occur, through which penetration of high-enthalpy acid fluids occurs into the sedimentary layer. These high-enthalpy fluids not only participate in the formation of secondary reservoirs in the Bazhenov-Abalak series dissolving and leaching components that are unstable under these conditions, but also directly take part in the processes of oil generation by organic matter thermolysis, and by introducing juvenile methane, its nearest homologues and hydrogen. The latter reacts with hydrogenation with organic matter, which results in formation of additional amount of hydrogen-saturated hydrocarbons.

Key words: secondary collectors; tectonic-hydrothermal processes; lithological types of rocks; nuclear magnetic resonance; pyrolysis.

For citation: Zubkov M.Yu. Reservoir types in the Bazhenov-Abalak series of Western Siberia and their genesis. Geologiya nefti i gaza = Oil and gas geology. 2019;(4):59–78. DOI: 10.31087/0016-7894-2019-4-59-78.

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M.Yu. Zubkov   Scopus

West-Siberian Geological Center, Tyumen, Russia;

zubkovmyu@mail.ru