Evidence for in situ methanogenic oil degradation in the Dagang oil field |
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| Institution: | 1. School of Biomedical Engineering, South-Central University for Nationalities, Wuhan 430074, China;2. National Key Laboratory of Science and Technology on Multi-spectral Information Processing, School of Automation, Huazhong University of Science and Technology, Wuhan\n430074, China;1. Department of Subsurface Geobiological Analysis and Research, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan;2. Laboratory of Ocean-Earth Life Evolution Research (OELE), Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan;3. Submarine Hydrothermal System Research Group, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan;4. Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Tokyo, Japan;5. Department of Systems Innovation, School of Engineering, University of Tokyo, Tokyo, Japan;6. Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA;7. Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA;1. Department of Physics, University of the Free State, Phuthaditjhaba 9866, South Africa;2. Department of Physics, University of the Free State, Bloemfontein ZA9300, South Africa;3. Department of Physics, Nelson Mandela University, Port Elizabeth 6031, South Africa;4. Department of Physics, Sefako Makgatho Health Sciences University, P.O. Box 94, Medunsa, 0204, South Africa;5. Department of Chemistry, University of Zululand, KwaDlangezwa 3886, South Africa;6. Department of Physics, City University of Hong Kong, 83 Tat Chee Ave., Kowloon, Hong Kong PR China |
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| Abstract: | In situ biotransformation of oil to methane was investigated in a reservoir in Dagang, China using chemical fingerprinting, isotopic analyzes and molecular and biological methods. The reservoir is highly methanogenic despite chemical indications of advanced oil degradation, such as depletion of n-alkanes, alkylbenzenes and light polycyclic aromatic hydrocarbon (PAH) fractions or changes in the distribution of several alkylated polycyclic aromatic hydrocarbons. The degree of degradation strongly varied between different parts of the reservoir, ranging from severely degraded to nearly undegraded oil compositions. Geochemical data from oil, water and gas samples taken from the reservoir are consistent with in situ biogenic methane production linked to aliphatic and aromatic hydrocarbon degradation. Microcosms were inoculated with production and injection waters in order to characterize these processes in vitro. Subsequent degradation experiments revealed that autochthonous microbiota are capable of producing methane from 13C labelled n-hexadecane or 2-methylnaphthalene and suggest that further methanogenesis may occur from the aromatic and polyaromatic fractions of Dagang reservoir fluids. The microbial communities from produced oil–water samples were composed of high numbers of microorganisms (on the order to 107), including methane producing Archaea within the same order of magnitude. In summary, the investigated sections of the Dagang reservoir may have significant potential for testing the viability of in situ conversion of oil to methane as an enhanced recovery method and biodegradation of the aromatic fractions of the oil may be an important methane source. |
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