δ13C and δD values of n-alkanes from in-reservoir biodegraded oils: Implications for understanding the mechanisms of biodegradation and for petroleum exploration

Pedentchouk, Nikolai, Bennett, Barry and Larter, Steve (2021) δ13C and δD values of n-alkanes from in-reservoir biodegraded oils: Implications for understanding the mechanisms of biodegradation and for petroleum exploration. Geosciences, 11 (9). ISSN 2076-3263

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Abstract

This study investigates the magnitude and direction of stable C and H isotope shifts of n-C 15–30 alkanes from biodegraded oils sourced from Type II (Oil suite S) and Type II/III (Oil suite H) kerogens. Compound-specific isotope data show a 2.0‰ 13C-enrichment and no D-enrichment of n-alkanes in the most biodegraded oil from sample suite S. Similarly, there is a 1.5–2.5‰ 13C-enrichment and no D-enrichment in Oil suite H. Overall, there is a <2.5‰ δ 13C and <20‰ δD variability among individual n-alkanes in the whole sequence of biodegradation. N-alkanes from the least biodegraded Oil H samples are 2–4‰ 13C-enriched in comparison with the least biodegraded Oil S. However, there are no differences in the δD values of n-alkanes in these samples. Our indirect isotopic evidence suggests (1) a site-specific biodegradation process, most likely at position C-2 and/or C-3 or another site-specific process, and (2) a significant D/H exchange between organic compounds in the source rock and isotopically similar marine formation waters. We conclude that, unlike δD methodology, investigation of δ 13C composition of n-alkanes has strong potential as a supplementary tool for oil–oil and oil–source-rock correlation even in biodegraded oils when n-alkanes are present.

Item Type: Article
Uncontrolled Keywords: carbon,correlation,hydrogen,isotopes,n-alkanes,oil biodegradation,earth and planetary sciences(all),sdg 14 - life below water ,/dk/atira/pure/subjectarea/asjc/1900
Faculty \ School: Faculty of Science > School of Environmental Sciences
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Depositing User: LivePure Connector
Date Deposited: 16 Sep 2021 11:17
Last Modified: 14 Oct 2021 01:10
URI: https://ueaeprints.uea.ac.uk/id/eprint/81440
DOI: 10.3390/geosciences11090365

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