| 川西坳陷南段天然气来源与碳同位素地球化学研究 |
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| 关键词:source and migration of natural gases carbon isotopic composition Western Sichuan Depression |
| 基金项目:国家自然科学基金资助项目(编号:49773188) |
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| 摘要: |
| Carbon Isotopic Geochemistry and Origin of Natural Gases in the Southern Part of the Western Sichuan Depression |
| The southern part of the Western Sichuan Depression is one of the major gas-producing provinces in Sichuan Basin. There previously existed several different opinions on the gas origin of this area. In order to get a better understanding of the source and migration of natural gases in this area, the authors analyzed carbon isotopic compositions of C 1-C 4 hydrocarbon and CO 2 components of these gases. Natural gas samples were collected from 16 producing wells of well- known Pingluoba, Daxingxi and Beimamiao gas fields. Together with chemical composition and geological information, the isotope data indicate that hydrocarbons of all three gas-fields seem to be entirely thermogenic and are derived from the Upper Triassic source rocks at a relatively great burial depth. Methane and ethane of these gas fields display different trends of isotopic compositional variations with depth. These changes can be attributed to the thermal cracking process during the formation and the dynamic process during the secondary migration of these hydrocarbons. The hydrocarbons in Pingluoba and Daxingxi gas fields are assumed to have migrated from deeply buried source rocks to shallower reservoirs. In addition, the hydrocarbons of Middle Jurassic reservoirs in the Pingluoba gas field have greater wetness and lighter isotopic composition than those of Upper Triassic reservoirs, which is believed to be the result of their generation from early mature source rocks and their mixing with late mature gases. Having high wetness and heavy isotopic composition, the Beimamiao hydrocarbons are supposed to have been migrating into the Late-Jurassic reservoirs along faults and fractures. |
| FAN Ran-xue,ZHOU Hong-zhong,CAI Kai-ping.2005.Carbon Isotopic Geochemistry and Origin of Natural Gases in the Southern Part of the Western Sichuan Depression[J].Acta Geoscientica Sinica,26(2):157-162. |
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