Impact of anaerobic biodegradation on alkylphenanthrenes in crude oil |
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| Institution: | 1. State Key Laboratory of Petroleum Resources and Prospecting, China University Petroleum Beijing, Fuxue Road 18, Changping, Beijing 102249, China;2. Chengdu Biogas Institute of the Agricultural Ministry, Chengdu 610041, China;3. School of Energy Resource, China University of Geosciences, Beijing 100083, China;4. Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada;1. School of Energy Resource, China University of Geosciences, Beijing 100083, China;2. Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada;3. Key Lab of Petroleum Geochemistry, CNPC, Beijing 100083, China;4. State Key Lab for Enhancing Oil Recovery, Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China;1. Schlumberger Reservoir Laboratories, 8087 – 54 Street, SE Calgary, Alberta T2C 4R7, Canada;2. Geological Survey of Canada, 3303-33 Street NW, Calgary, Alberta T2L 2A7, Canada;1. School of Energy Resources, China University of Geosciences (Beijing), Beijing, 100083, China;2. Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China;3. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China;4. Northwest Petroleum Company, SINOPEC, Urumqi, 830011, China;5. Key Laboratory of Exploration Technologies for Oil and Gas Resources of Ministry of Education, Yangtze University, Wuhan, 430100, China |
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| Abstract: | The biodegradation of crude oil by microorganisms from well Luo-801, China, was examined in cultures grown under conditions that promoted either methanogenesis or sulfate reduction, at 35 °C and 55 °C. Headspace gas and oil compositions were characterized at 180 d and 540 d. Alkylphenanthrenes are relatively recalcitrant to bacterial attack and the biodegradation of these compounds appeared to be insignificant after 180 d under both conditions, but is evident after 540 d. The depletion of alkylphenanthrenes was monitored through evaluation of the ratio of alkylphenanthrenes to the most bioresistant, analyzed component (C28 20R triaromatic steroid hydrocarbon) and isomer susceptibility also was evaluated by relative abundance comparison within the compound class. The influence of growth temperature varied. Only slight differences in alkylphenanthrene concentrations were observed after 180 d whereas the greater degrees of biodegradation were observed at 35 °C in the methanogenic culture and at 55 °C in the sulfate reducing culture. Overall, higher biodegradation rates occur under sulfate reducing condition, which is consistent with the conclusion that methanogens are generally less able to compete for substrates than sulfate reducers. The biodegradation susceptibility of alkylphenanthrenes decreases with increasing degree of alkylation, i.e., phenanthrene (P) and methylphenanthrenes (MPs) were more easily biodegradable than C2-alkylphenanthrenes (C2-Ps) and C3-alkylphenanthrenes (C3-Ps). Biodegradation selectivity for specific homologues is not striking for the limited time duration of the experiments. However, 3-MP seems slightly more vulnerable than other methylphenanthrene isomers and 1,7-DMP has slightly higher ability to resist biodegradation than the other C2-P isomers. The commonly used thermal maturity parameters derived from methylphenanthrene isomer ratios are altered insignificantly by biodegradation and remain valid for geochemical assessment. This information should be useful for assessing the limits of in situ crude oil biodegradation. |
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