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GEOCHEMISTRY OF ORGANIC MATTER FROM JURASSIC AND CRETACEOUS ROCKS IN THE SOUTH OF YAMAL PENINSULA (VOSHODNAYA-3021 WELL)

A. I. Burukhina, E. A. Fursenko

Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia

In order to determine the genetic type, paleofacial conditions of accumulation and catagenic maturity of the OM from Jurassic-Cretaceous section in southern Yamal Peninsula, the study of rock samples from Lower Cretaceous Tanopchinskaya and Akhskaya formations, Upper Jurassic Bazhenovskaya formation, and Middle Jurassic Malyshevskaya formation in the Voshodnaya-3021 well was carried out with the use of organic geochemistry methods. An uneven distribution of OM within the studied strata has been established: the rocks of the Bazhenov formation, as expected, are enriched to the greatest extent, while the concentrations of organic carbon in the rocks of the Lower Cretaceous and Middle Jurassic parts of the section are significantly lower. Based on the set of pyrolytic, isotopic and molecular-bitumenological data the studied OM was shown to have: predominantly aquatic genesis in the rocks of the Bazhenov formation, a significant contribution of marine biomass to the composition of the Akhskaya formation, and, at the contrary, predominantly terrestrial source in the Tanopchinskaya and Malyshevskaya formations. The accumulation of the OM under consideration occurred under weakly regenerative conditions, in a sedimentary basin with terrigenous sedimentation and normal water salinity. The level of thermocatalytic maturity of the studied OM, expectedly increases from top to bottom along the well section, reaching main oil generation zone in the section of the Bazhenov formation. Taking into account the full range of information received, the current generation potential of the Lower Cretaceous and Middle Jurassic strata studied is estimated to range from low to moderate. For the rocks of the Bazhenov formation, higher values of hydrogen index, a relatively high TOC content, and a predominantly aquatic composition of OM allow us to assume current oil-and-gas generation potential being from good to high.

Keywords: organic geochemistry, organic matter, hydrocarbon-biomarkers, petroleum potential, Yamal peninsula, West Siberia.

DOI 10.20403/2078-0575-2025-1-13-25

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