Oil & Gas Geology ›› 2007, Vol. 28 ›› Issue (5): 664-668,674.doi: 10.11743/ogg20070518

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Geochemical characteristics of natural gas from different structural units of the Kuqa Depression,the Tarim Basin

Bao Jianping1, Zhu Cuishan1, Zhang Qiucha2, Li Mei2, Lu Yuhong2   

  1. 1. Key Laboratory of Exploration Technologies for Oil and Gas Resources in Ministry of Education, Yangtze University, Jingzhou, Hubei 434023, China;
    2. Institute of Petroleum Exploration & Development, Tarim Oilfield Company, PetroChina, Korla, Xinjiang 841000, China
  • Received:2007-07-13 Online:2007-10-25 Published:2012-01-16

Abstract:

Analysis of the geochemical characteristics of natural gas from the main structural units of the Kuqa Depression in Tarim Basin shows that the natural gas from Dabei-Kelasu structural belt is dominated by methane and has a dryness coefficient [C1/(C1-C5)] near 1.00,indicating typical dry gas;while that from the frontal uplift zone has a relatively low content of methane and a dryness coefficient less than 0.95,indicating typical wet gas.In terms of carbon isotope compositions,the gas from the Dabei-Kelasu structural belt contains significantly heavier methane and ethane isotopes(>-31‰ and-20‰,respectively),while that from the frontal uplift zone has obviously lighter methane and ethane isotopes(<-33‰ and-20‰,respectively).Maturity calculation reveals that the gas from the Dabei-Kelasu structural belt belongs to over-mature gases with a vitrinite reflectance ranging between 1.65% and 2.25%,while that from the frontal uplift zone belongs to highly-mature gas with a vitrinite reflectance ranging from 1.00% to 1.35%.All these indicate that the natural gases in different structu-ral units in the Kuqa Depression were generated from the organic matters in the source rocks at different thermal evolution stages.

Key words: carbon isotope, maturity, dryness coefficient, natural gas, Kuqa Depression, Tarim Basin

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