Geochemical characteristics and possible origin of natural gas in the Taibei Depression,Turpan-Hami Basin,China |
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| Authors: | Hongjing Zhao Min Zhang Zhiyong Wang |
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| Institution: | 1.China University of Geosciences,Wuhan,China;2.Geochemical Department of Yangtze University,Jingzhou,China;3.The Key Laboratory of Exploration Technologies for Oil and Gas Resources (Yangtze University),Ministry of Education,Jingzhou,China;4.Research Institute of Petroleum Exploration and Development,TuHa Oil field,Hami,China |
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| Abstract: | 292 chemical composition data and 82 isotopic composition data of gas samples collected from the Taibei Depression of the
Turpan-Hami Basin, West China, were used in the study of their origin. Non-hydrocarbon gas is poor in most samples whereas
abundant nitrogen in some samples is positively correlated with δ13C1. Although methane is the main constituent, higher molecular gaseous hydrocarbons, from ethane to pentane, are detected in
most samples, in accordance with the distribution of oil reservoirs. The stable carbon isotope ratios of methane, ethane and
propane are defined as δ13C1: ?45.5‰ to ?33.5‰, δ13C2: ?30.2‰ to ?10.5‰, and δ13C3: 27.6‰ to ?11 respectively. According to the distribution of carbon isotope ratios, 2 families of gas can be grouped, most
showing normal distribution of carbon isotopes, and others having obvious heavier carbon isotopes and being of abnormal distribution.
Based on the isotopic composition, the disagreement between the relationship of Δ(δ13C1-δ13C2) and δ13C2 and that of δ(δ13C1-δ13C2) and δ13C2, and the calculated Ro, there are oil-associated gas, coal-derived gas and mixture of them. Other samples with obviously
heavier isotopic compositions from the Yanmuxi oilfield of the Taibei Depression have been degraded by organisms. |
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| Keywords: | Taibei Depression natural gas carbon isotope mixed gas biodegraded gas |
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