Oil & Gas Geology ›› 2017, Vol. 38 ›› Issue (2): 355-362.doi: 10.11743/ogg20170215

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Geochemical characteristics and petroleum geologic significance of natural gas in the north margin of the Qaidam Basin

Tian Jixian1, Li Jian1, Zeng Xu1, Guo Zeqing1, Zhou Fei2, Wang Bo2, Wang Ke2   

  1. 1. Langfang Branch of Research Institute of Petroleum Exploration and Development, PetroChina, Langfang, Hebei 065007, China;
    2. Exploration and Development Research Institute, Qinghai Oilfield Company, PetroChina, Dunhuang, Gansu 736200, China
  • Received:2016-05-08 Revised:2016-09-25 Online:2017-04-28 Published:2017-05-04

Abstract: In order to understand the generation and distribution of natural gas in the northern margin of the Qaidam Basin,the geochemical characteristics of natural gas are analysed with both natural gas composition and carbon isotope.The results show that the natural gas is dominated by methane,but the content of heavy hydrocarbons is relatively high.There are obvious differences in natural gas composition in different structural belts.Research on carbon isotopes indicated that the δ13C1 and δ13C2 values are -36.4‰~-19.3‰ and -27.4‰~-19.82‰,respectively.The identification of na-tural gas shows that the main type of natural gas in this area is coal-generated gas and is derived from Jurassic source rocks.Carbon isotopic distribution of the northern margin of the Qaidam Basin is characterized by positive sequence,and there are carbon isotope reversal phenomena in some areas due to different maturity,different mixture types of sources and the gas generation from source rocks in the high-mature stage.The distribution of oil and gas reserves in the northern margin of the Qaidam Basin is characterized by spatial zonation from the outer edges to the centre of the basin and is controlled by the source rock maturity.The natural gas is located in mature and high maturity areas.Future promising areas for exploration have been put forward,which include Lenghu NO.6 and NO.7,Eboliang-Hulushan tectonic belt and the foreland of the Altun Mountains.

Key words: natural gas origin, carbon isotope, source rock, oil and gas distribution, northern margin of the Qaidam Basin

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