Silurian graptolitic shales of the junction zone of the Gydan and the Enisey-Khatanga oil and gas bearing regions as a possible source of oil and gas

Introduction. Silurian graptolitic shales represent a source of oil and gas in various petroleum basins of the world. They are also widely distributed in the northern Eastern Siberia within the Lena-Tunguska basin, Folded Taimyr and, probably, in the adjacent parts of the Enisey-Khatanga and West Siberian oil and gas basins. Stratigraphically, they are confined to the Llandovery deposits, although in various areas characterized by elevated sea depths (in particular, in Taimyr), they are also common in the Wenlock and Ludlow deposits.
The aim of this paper is to present the results of geochemical and coal petrographic studies performed on the basis of a new well drilling data.
Materials and methods. Graptolitic shales in the well on Leskinsky license area were drilled in the 140-m interval of the Ust`-Enisey Formation (S1ue) of the Telychian Stage of the Llandovery and the Homerian Stage of the Wenlock, Lower Silurian. Petrographic and geochemical studies, including pyrolytic, bituminological, chromatomass-spectrometry and isotope studies of samples, and their complex interpretation were carried out.
Results. Comprehensive studies of graptolitic shales made it possible to establish that they are characterized by a high content of organic matter; marine, predominantly algal, type of organic matter accumulated in suboxic, possibly, freshwater conditions; a high degree of organic matter maturity complicated by local heating in the upper part of the studied section.
Conclusions. The obtained data allow us to consider the Lower Silurian graptolitic shale units as one of the main sources of hydrocarbons in the lower part of the section of the study area.

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