—We present results of study of the molecular composition of organic matter (OM) in the bottom sediments of the Laptev Sea by gas chromatography–mass spectrometry, isotope gas chromatography–mass spectrometry, and Rock-Eval pyrolytic analysis. The OM of all collected sediment samples shows a significant terrigenous contribution. Compounds that are biomarkers of methanotrophic microorganisms are also found. A positive correlation between the contents of the studied biomarkers and the contents of pelite and total organic carbon is observed at the sites with documented intense methane bubbling. For example, the average content of C30 hopenes at the “methane” stations is twice higher than that at the “background” ones. The average content of C32 αβ-hopanes in sediment samples from the methane seepage area is 1.5 times higher than that at the background stations. We suggest that the increased C30 αβ-hopane content (~1.5 times higher within the methane seepage area) and the decreased moretane index relative to the C31 hopane index are due to the inflow of OM of petroleum origin. The presence of biphenyl in sediments indicates its petroleum origin, which supports our assumption of the migratory nature of petroleum hydrocarbons in the methane seepage area. Triterpenoids found in the sediment OM indicate diagenetic bacterial transformation of OM in the methane seepage areas, which shows that methane has been released for a long time. We assume the intense activity of the consortium of methanotrophs and sulfate reducers in the methane seepage areas.
South-east of Western Siberia (Tomsk Region) faces good prospects for developing shale oils from Bazhenov formation. Ample preconditions are available there: high content of organic matter of excellent oil-generating quality in Bazhenov formation rocks and main oil formation stage of primary rocks. However, drilling success appreciably depends on the correct choice of the well spud-in place.
Regional geochemical investigations of Bazhenov formation and of Bazhenov genetic type of oils may considerably confine the area of search by choosing the most promising areas for detecting shale oil deposit.
Recent investigations permitted to identify a regional pattern of changes in Bazhenov formation rocks catagenesis and to grade the prospective regional oil-bearing capacity associated with hydrocarbon generation by Bazhenov formation rocks. Identification of regularities in expansion of Bazhenov - type oils as well as comparison between the maturity of oils and the maturity of organic matter of Bazhenov formation rocks permitted to mark out areas that are promising for the formation of both oil deposit in traditional oil reservoirs and of shale oil deposit.
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