Geochemical comparison between gas in fluid inclusions and gas produced from the Upper Triassic Xujiahe Formation,Sichuan Basin,SW China |
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| Institution: | 1. Sinopec Petroleum Exploration & Production Research Institute;2. Petro China Research Institute of Petroleum Exploration and Development;3. Sinopec Petroleum Exploration & Production Research Institute;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, 18 Fuxue Road, Beijing 102249, China;2. Department of Organic Geochemistry and Environmental Science, College of Geosciences, China University of Petroleum, 18 Fuxue Road, Beijing 102249, China;3. WA – Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;4. Department of Chemistry, Oregon State University, Corvallis, OR 97331, USA;5. Department of Organic Geochemistry, Yangtze University, Jingzhou, Hubei 434023, China;1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, PR China;2. University of Chinese Academy of Sciences, Yuquan Road, Beijing 100049, PR China;1. School of Energy Resources, China University of Geosciences, Beijing 100083, China;2. Technical Center, CNCP LOGGING, Xi''an, Shaanxi 710077, China;3. Research Institute of Shaanxi Yanchang Petroleum (Group) CO., LTD., Xi''an, Shaanxi 710075, China;1. Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China;2. China University of Petroleum, Beijing 102249, China;1. School of Earth Sciences and Engineering, Xi''an Shiyou University, Xi''an 710065, China;2. South Company of Prospecting, Sinopec, Chengdu 610041, China;3. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China;4. Sinochem Petroleum Exploration & Production Co., Ltd., Beijing 100031, China |
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| Abstract: | Natural gas in the Xujiahe Formation of the Sichuan Basin is dominated by hydrocarbon (HC) gas, with 78–79% methane and 2–19% C2+ HC. Its dryness coefficient (C1/C1–5) is mostly < 0.95. The gas in fluid inclusions, which has low contents of CH4 and heavy hydrocarbons (C2+) and higher contents of non-hydrocarbons (e.g. CO2), is a typical wet gas produced by thermal degradation of kerogen. Gas produced from the Upper Triassic Xujiahe Formation (here denoted field gas) has light carbon isotope values for methane (δ13C1: ?45‰ to ?36‰) and heavier values for ethane (δ13C2: ?30‰ to ?25‰). The case is similar for gas in fluid inclusions, but δ13C1 = ?36‰ to ?45‰ and δ13C2 = ?24.8‰ to ?28.1‰, suggesting that the gas experienced weak isotopic fractionation due to migration and water washing. The field gas has δ13CCO2 values of ?15.6‰ to ?5.6‰, while the gas in fluid inclusions has δ13CCO2 values of ?16.6‰ to ?9‰, indicating its organic origin. Geochemical comparison shows that CO2 captured in fluid inclusions mainly originated from source rock organic matter, with little contribution from abiogenic CO2. Fluid inclusions originate in a relatively closed system without fluid exchange with the outside following the gas capture process, so that there is no isotopic fractionation. They thus present the original state of gas generated from the source rocks. These research results can provide a theoretical basis for gas generation, evolution, migration and accumulation in the basin. |
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| Keywords: | Upper Triassic Xujiahe Formation Gas in fluid inclusions Field gas Carbon isotope Geochemical comparison Sichuan Basin |
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