Geochemical features of bitumen shows in the Lower-Middle Devonian deposits of the Northern-Western part of Kotelny Island (Novosibirsk Island Archipelago)

Abstract

The work presents the results of organic matter (OM) study of rocks, the composition, chemical structure of chloroform bitumen (CB), their fractions and the nature of the hydrocarbon biomarkers distribution in samples taken from outcrops. The obtained results confirmed the existing idea of ​​the domanicoid nature of OM and the high oil and gas potential of the studied deposits. According to our data, the aquagenic type of OM is indicated by a high content of Corg, a high yield of CB, a high content of oils in the composition of synbitumoids, and the predominance of relatively low molecular weight n-alkanes with a maximum at nС15-18. A sufficient maturity of bitumen can be judged by CPI coefficients close to unity and low absorption coefficients of oxygen-containing groups and bonds in the CB, thus deposits entered the main oil generation zone and generated liquid hydrocarbons that could migrate and form clusters. According to the data of Chromato Mass Spectrometry, it is shown that a feature of the composition of CB from the Lower Devonian sediments is the presence of high concentrations of dibenzothiophenes, in contrast to the Middle Devonian, which may be associated with the formation of the initial OM in an environment with higher hydrogen sulfide contamination of sediments. It has been suggested that naphthides generated by aquagenic OM of the Lower Devonian deposits can be enriched with dibenzothiophenes. The studied bitumen shows are mainly syngenetic in nature and have been influenced by hypergenic oxidation (judging by the nature of the IR spectra of resinous components) and contact metamorphism. According to the characteristics of the distribution of saturated hydrocarbons, it was shown that, in the Middle Devonian, bitumen occurrences along with chemical oxidation were affected to a different degree of bacterial oxidation processes, in contrast to the Lower Devonian bitumen shows. The results can be used to assess the generation potential of oil source strata and to forecast the prospects of oil and gas potential in the shelf of the eastern sector of the Russian part of the Arctic.

Keywords

• Kotelny Island
• Lower and Middle Devonian
• organic matter
• bitumen shows
• hydrocarbon biomarkers