TY - JOUR
T1 - δ13C and δD values of n-alkanes from in-reservoir biodegraded oils: Implications for understanding the mechanisms of biodegradation and for petroleum exploration
AU - Pedentchouk, Nikolai
AU - Bennett, Barry
AU - Larter, Steve
PY - 2021/9
Y1 - 2021/9
N2 - 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.
AB - 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.
KW - Carbon
KW - Correlation
KW - Hydrogen
KW - Isotopes
KW - N-alkanes
KW - Oil biodegradation
UR - http://www.scopus.com/inward/record.url?scp=85114516586&partnerID=8YFLogxK
U2 - 10.3390/geosciences11090365
DO - 10.3390/geosciences11090365
M3 - Article
VL - 11
JO - Geosciences
JF - Geosciences
SN - 2076-3263
IS - 9
M1 - 365
ER -