Changes in Concentration and Distribution of Biomarkers in Biodegraded Oils from Dongying Depression, China
2015
Chen, Zhonghong | Wang, T.-G. | Yan, Detian
The alkane fraction of 11 biodegraded oils and five non-biodegraded oils from the Dongying Depression, Bohai Bay Basin, eastern China, were analyzed by gas chromatography–mass spectrometry to investigate the biomarker alteration caused by biodegradation. Results indicated that the concentration of 25-norhopanes was correlated with increased biodegradation. The oil samples showed an increase in the C₃₁ and C₃₂ hopane 22S/(22S + 22R), C₂₉ sterane C₂₉20S/(20S + 20R), and C₂₉ββ/(ββ + αα) thermal maturity parameters in the heavily biodegraded oils. Oleanane was preferentially biodegraded compared with C₃₀17α-hopane, which was preferentially biodegraded compared with C₂₉17α, 21β-norhopane, C₃₀ moretane, and C₂₉ 25-norhopane. The selective depletion of C₂₇–C₂₉ steranes followed the order ααα 20R > ααα 20S + αββ 20R > αββ 20S and C₂₇ > C₂₉ > C₂₈, and the diasteranes and C₂₀–C₂₁ steranes were much more resistant to biodegradation than regular C₂₇–C₂₉ steranes. The steranes were generally preferentially biodegraded compared with the hopanes in this study.
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