Discovery and geochemical characteristics of the Upper Jurassic Suowa Formation reservoir in Qiangtang Basin, Xizang(Tibet)
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    Abstract:

    Objectives: At present, the discovered reservoirs are mainly stored in the Middle Jurassic Buqu Formation in the South Qiangtang basin. However, with the research, the thrust nappe structure developed in the South Qiangtang Basin strongly reformed and destroyed the ancient reservoirs of the Buqu Formation. Based on the geochemical study of the Suowa Formation of the Upper Jurassic in the North Qiangtang Basin, this paper discusses the oil and gas exploration potential of the north Qiangtang Basin and the Suowa Formation.Methods:The oil reservoir samples were pretreated and crushed to 100 mesh, and the Soxhlet extraction was completed for 72 h. The soluble organic matter chloroform asphalt “A” was extracted with trichloromethane, and then asphaltene was precipitated with n- hexane, then the obtained soluble organic matter was put on the chromatographic column, and the group components were separated by n- hexane, dichloromethane and n- hexane, dichloromethane to obtain saturated hydrocarbon, aromatic hydrocarbon and non hydrocarbon fractions. Then the saturated hydrocarbon fraction was analyzed by gas chromatography- mass spectrometry (GC- MS) to obtain biomarkers.Results: The analysis of biomarker parameters shows that the sedimentary environment of organic matter in the reservoir is a strong reducing environment with a certain salinity. Among them, the source of organic matter in Caiduochaka(Caiduo Salt Lake) reservoir is mainly from lower aquatic organisms; while the source of organic matter in Shuanghu and Yahu reservoirs is jointly imported by lower aquatic organisms and higher plants; the contribution of organic matter in reservoir in Amu Lake(Amu Co) area is terrigenous organic matter mainly. The analysis of maturity parameters shows that the thermal evolution of organic matter in reservoir samples has reached the low maturity maturity stage.Conclusions:The analysis of biomarker parameters shows that the sedimentary environment of organic matter in the reservoir is a reductive environment with a certain salinity, while the source of organic matter has the joint input of lower aquatic organisms and higher plants, which may be affected by the secondary hydrocarbon generation of source rocks caused by thrust nappe structure, which indicates that there may be both terrestrial and marine source rocks in the study area; the maturity parameter analysis shows that the oil reservoir is composed of both terrestrial and marine source rocks. The thermal evolution of organic matter in the samples has reached the low maturity maturity stage, indicating that the maturity of source rocks has reached the threshold of oil generation, suggesting that these source rocks have generated hydrocarbon in a certain scale. The paleo-oil reservoirs in Shuanghu area are generally affected by the thrust nappe structure from north to south. The Suowa Formation in the North Qiangtang Basin, located in the root zone of the thrust nappe structure, is well exposed and has good trap conditions. Therefore, the discovery and geochemical characteristics of the Suowa Formation in Shuanghu area are of great significance for the exploration of Upper Jurassic oil and gas resources in the North Qiangtang Basin.

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YANG Yizhuo, ZHAO Zhen, WU Zhenhan, TANG Youjun.2020. Discovery and geochemical characteristics of the Upper Jurassic Suowa Formation reservoir in Qiangtang Basin, Xizang(Tibet)[J]. Geological Review,66(5):1230-1240.

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History
  • Received:July 07,2020
  • Revised:August 03,2020
  • Adopted:
  • Online: September 19,2020
  • Published: