Origins of hydrocarbons in the Sagara oil field, central Japan |
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Authors: | Tomohiro Toki Toshitaka Gamo and Urumu Tsunogai |
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Institution: | Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo 060-0810, Japan (email: ) |
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Abstract: | Abstract We collected free-gas and in situ fluid samples up to a depth of 200.6 m from the Sagara oil field, central Japan (34°44'N, 138°15'E), during the Sagara Drilling Program (SDP) and measured the concentrations and stable carbon isotopic compositions of CH4 and C2H6 in the samples. A combination of the CH4/C2H6 ratios with the carbon isotope ratios of methane indicates that the hydrocarbon gases are predominantly of thermogenic origin at all depths. The isotope signature of hydrocarbon gases of δ13 < δ13 suggests that these gases in the Sagara oil field are not generated by polymerization, but by the decomposition of organic materials. |
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Keywords: | carbon isotope free-gas hydrocarbons in situ fluid microbial origin Sagara Drilling Program Sagara oil field thermogenic origin |
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