Study on Oxidation Rate and Isotope Fractionation of Methane in Bohai Sea Sediments

Yu-feng CHEN; Xiu-li ZHENG; Jing LI; Xing-liang HE; Chang-ling LIU; Qing-guo MENG; De-di QIN; Pei-yu ZHANG

doi:10.15898/j.cnki.11-2131/td.201707100117

Yu-feng CHEN, Xiu-li ZHENG, Jing LI, Xing-liang HE, Chang-ling LIU, Qing-guo MENG, De-di QIN, Pei-yu ZHANG. Study on Oxidation Rate and Isotope Fractionation of Methane in Bohai Sea Sediments[J]. Rock and Mineral Analysis, 2018, 37(2): 164-174. DOI: 10.15898/j.cnki.11-2131/td.201707100117

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Study on Oxidation Rate and Isotope Fractionation of Methane in Bohai Sea Sediments

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BACKGROUND The Bohai Sea contains a large amount of oil and gas, the main component of which is methane. The influence of natural or human factors will cause its leakage and migration and then have a negative impact on the environment. However, most of the methane would be oxidized by microorganisms during the leakage and migration processes. Meanwhile, the different environmental conditions will affect oxidation rate and carbon isotope fractionation of methane. OBJECTIVE In order to better understand the law of isotope fractionation and methane oxidization in the sediments and to provide reference for further related research in this area, the Bohai Sea sediments were selected as laboratory raw materials for the degradation of laboratory experiments and are described in this paper. METHODS Gas Chromatography and Gas Chromatography-Isotope Ratio Mass Spectrometry were used to determine the methane oxidation rate, and the carbon isotope fractionation coefficient ε of methane was determined. RESULTS The results show that the aerobic oxidation of methane is dominant. Oxidation temperature and gas flow rate are the main factors affecting the rate of methane oxidation. In the mode of continuous incubation, when the temperature reduced from 28℃ to 15℃, the average oxidation rate reduced by 60%±10%, indicating that the lower temperature is not helpful for methane oxidation. When the gas flow rate increases from 50 to 150 μL/min, the average oxidation rate of methane increases by 90%±10%. This indicates that the higher gas flow rate is favorable to the increase of oxidation rate. It is also found that the fractionation effect of carbon and hydrogen isotopes are mainly affected by temperature where the fractionation degree is positively correlated with temperature. CONCLUSIONS Temperature is an important factor affecting methane oxidation rate and isotopic fractionation.

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Study on Oxidation Rate and Isotope Fractionation of Methane in Bohai Sea Sediments

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