Biodegradation influence on alkylphenanthrenes in oils from Bongor Basin, SW Chad

Haiping Huang,Zhigang Wen,Renfang Pan,Zhiqiang Li,Denglin Han

doi:10.1038/s41598-019-49495-1

Haiping Huang, Zhigang Wen + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-49495-1

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Journal: Scientific Reports	Publication Date: Sep 10, 2019
Citations: 5	License type: open-access

Affiliation: University of Calgary, Yangtze University

Abstract

Oil samples from the Bongor Basin, SW Chad have been geochemically characterized to investigate the biodegradation influence on alkylphenanthrenes. Concentrations of C0–3-alkylphenanthrenes (C0–3Ps) increase markedly after level 6 biodegradation due to the removal of other vulnerable components, decrease sharply after level 7 biodegradation and approach to absence at level 8. Phenanthrene appears to have higher ability to resist biodegradation than C1–3Ps at certain biodegradation levels (≤level 7) due to demethylation, which has been inferred as a possible reaction process during biodegradation of the aromatic hydrocarbons. The enrichment of non-alkylated phenanthrene in biodegraded oils makes biodegradation assessment complicated on the basis of alkylphenanthrene distributions. Individual isomers in alkylphenanthrenes exhibit variable ability to resist biodegradation influence. While certain isomers do show higher ability to resist biodegradation than others, no uniform biodegradation sequence can be established. Meanwhile, the biodegradation susceptibility between hopanes and alkylphenanthrenes varies greatly in different samples. The biodegradation systematics of alkylphenanthrenes proves to be highly complex, which may be indicative of the multiple charges and mixing during biodegradation.

Highlights

Alkylphenanthrenes, characterized by fused-ring chemical structures, are the most common and abundant polycyclic aromatic hydrocarbons (PAHs) in source rock extracts and oils, which are originated from diagenesis and catagenesis alterations of sedimentary organic matter in depositional basins or combustion of fossil fuels and/or biomass
It is widely accepted that the biodegradation rate decreases with increasing degree of alkylation, i.e., phenanthrene and methylphenanthrenes are removed before C2- and C3Ps are attacked[14,22,23]
Biodegradation exerts the primary control on alkylphenanthrene concentrations and distributions in oils from the Bongor Basin, SW Chad

Summary

Introduction

Alkylphenanthrenes, characterized by fused-ring chemical structures, are the most common and abundant polycyclic aromatic hydrocarbons (PAHs) in source rock extracts and oils, which are originated from diagenesis and catagenesis alterations of sedimentary organic matter in depositional basins or combustion of fossil fuels and/or biomass. The effect of biodegradation can be assessed by using the occurrence and/or absence of certain hydrocarbon components, isomer distributions and relative abundance of compound classes. Larter et al.[14] noted that many samples from northern Alberta have been biodegraded to a uniform PM level but show great variable extent of alteration in aromatic compounds. They proposed the Manco (Modular Analysis and Numerical Classification of Oils) biodegradation scale by visual examination of compound completeness in various compound classes. Whether the biodegradation sequence of C2- and C3Ps established based on the observation from Liaohe oilfield[15] exhibiting similar behavior as methylphenanthrene isomers in different basins has not been fully investigated in the literature. Caution should be taken when compound distribution pattern was applied for biodegradation influence assessment

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