Oil & Gas Geology ›› 2014, Vol. 35 ›› Issue (1): 124-130.doi: 10.11743/ogg20140115

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Analysis and application of components and isotopic compositions of fluid inclusions in volcanic reservoirs of the Xujiaweizi fault depression

Li Jijun1, Cao Xicheng2, Wang Weiming1, Shi Lei3, Li Jingkun4, Huo Qiuli4   

  1. 1. Research Institute of Unconventional Oil & gas and New Energy, China University of Petroleum, Qingdao, Shandong 266580, China;
    2. College of Earth Sciences, Northeast Petroleum University, Daqing, Heilongjiang 163318, China;
    3. No.3 Oil Production Plant, PetroChina Daqing Oilfield Company, Daqing, Heilongjiang 163314, China;
    4. Research Institute of Petroleum Exploration & Development, PetroChina Daqing Oilfield Company, Daqing, Heilongjiang 163712, China
  • Received:2013-06-21 Revised:2013-12-27 Online:2014-02-08 Published:2014-03-26
  • Contact: 王伟明(1981—),男,博士、讲师,油气地质与地球化学。E-mail:wangweiming6686@163.com。 E-mail:wangweiming6686@163.com

Abstract: A comparative analysis of components and isotopic compositions of gas inclusion in volcanic reservoirs of the Xujiaweizi fault depression before and after thermal decrepitation was performed by using the vacuum mechanical crushing method.The origin of natural gas was further discussed in combination with the corresponding characteristics of natural gas produced from wells and the results of thermal simulating test.The hydrocarbon content of gas from magma degassing is high,indicating that some hydrocarbon gases may be of inorganic origin,thus it is necessary to further research on the differences between gas from volcanic action and that from magmatic action.The main cause of reversal carbon isotopic sequence of hydrocarbon gas in the study area is the mixing of natural gases generated in different times or from different sources,rather than the component and isotopic fractionation during dissipation of natural gas through the caprock.Therefore,the reversal phenomenon can not be used individually to confirm the genesis of natural gas.In comparison with organic gas,inorganic gas(including CH4,C2H6,CO2)often has a heavier carbon isotopic value.It is applicable to some extent to use the the δ13C1 value over -20‰ as the criteria for determining inorganic gas,but this criteria is over strict.The CO2 in Xujiaweizi fault depression is mainly sourced from magma degassing.The inorganic CO2 did not experience primary migration and had no chance to contact with formation water,being favorable for their accumulation.These understandings are helpful to determine the origin of natural gas in Xujiaweizi fault depression.

Key words: carbon isotope, fluid inclusion, natural gas origin, volcanic rock, Xujiaweizi fault depression

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