Oil & Gas Geology ›› 2015, Vol. 36 ›› Issue (6): 934-944.doi: 10.11743/ogg20150608

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Geological and geochemical characteristics of silicified hydrothermal fluids in Well Shunnan 4,Tarim Basin

Li Yingtao1,2, Ye Ning1,2, Yuan Xiaoyu3, Huang Qingyu4, Su Bingrui5, Zhou Ruiqi6   

  1. 1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    2. Energy College, Chengdu University of Technology, Chengdu, Shichuan 610059, China;
    3. Institute of Petroleum Geology in Wuxi, SINOPEC, Wuxi, Jiangshu 214151, China;
    4. Research Institution of Petroleum Exploration & Development, PetroChina, Beijing 100083, China;
    5. Deposition College, Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    6. Sichuan Provincal Survey and Design Research Institute of Coalfield Geologic Engineering, Chengdu, Sichuan, 610059, China
  • Received:2015-08-20 Revised:2015-10-30 Online:2015-12-08 Published:2016-01-08

Abstract: Cores from the Ordovician Yingshan Formation limestone in the of Well Shunnan 4 of the Tarim Basin show remarkable signs of hydrothermal alteration and metasomatism of silicon.Dissolved fracture-cavity,loose siliceous limestone/siliceous rock,hydrothermal veins and large quartz crystal cluster were abnormally developed.Observation of geological characteristics of the samples and analyses of fluid inclusion/rare earth elements and trace element,all suggested a mixed origin of the thermal fluids.It is believed that igneous activities provided energy and volcanic thermal fluid together with formation water formed a mixture of low-to-medium temperature and high salinity silicified hydrothermal fluid.REE analyses reveal that δEu values range from 0.040 to 0.118 and average 0.069-negative anomaly that indicates a reductive environments; Sm/Nd ratios range between 0.169 and 0.256 and average 0.194,indicating a crustal diagenetic fluids.The high similarity between the average REE distribution curve of samples and those of earth's crust suggests the origin of heat from magma,and to be more specific,the upper crust as indicated by a lack of Mg2+ in the samples.Ba/Sr values range from 0.43 to 19.76 and average 6.70.Such a wide variation means the relative complexity of the fluid.U/Th ratios range from 0.35 to 4.76 and average 2.14.Th/U ratios range from 0.21 to 2.88 and average 1.03.And Th/U-Y/Ho correlations all indicate that the fluid is of low-temperature type.

Key words: trace element, rare earth element, silicification hydrothermal fluid, fluid inclusion, siliceous rock, Shunnan area, Tarim Basin

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