Lithologic Reservoirs ›› 2016, Vol. 28 ›› Issue (5): 34-43.doi: 10.3969/j.issn.1673-8926.2016.05.004

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Genesis of dolomite of Changxing Formation in Tieshan-Shuangjiaba area, northeast Sichuan Basin

Zhang Yulu1, Wen Huaguo1, Zheng Rongcai1, Zhou Gang2, Zhang Bing1, Cao Jixiang1   

  1. (1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology,Chengdu 610059,China;2. Research Institute of Exploration and Development, PetroChina Southwest Oil and Gas Field Company, Chengdu 610041, China)
  • Online:2016-09-29 Published:2016-09-29

Abstract:

As the main reservoir rock of Changxing Formation in the northeast Sichuan, the dolomite of reef flat facies has received more attention. Therefore, it is of great significance to comprehensively analyze its genesis in order to promote the natural gas exploration and development. The dolomite of Changxing Formation in Tieshan?Shuangjiaba area was analyzed from the aspects of structure, genesis and diagenesis. Based on the analysis of the dolomite order degree, cathodeluminescence, SEM, trace elements and stable isotopes, it is demonstrated that the dolomitization of dolomicrite of Changxing Formation took place in the relatively closed and strongly evaporated restricted sea basin behind the platform margin reef. The initial rocks of biogenic dolomite and crystalline dolomite are identified to be reef limestone and bioclastic limestone, which are originally deposited in the platform margin reef flat or intra platform reef flat. Geochemical characteristics of the dolomite inheriting properties of initial rocks significantly varied in different facies, which can be attributed to different sedimentary characteristics, namely the isolation and evaporation of the intra platform reef as well as the exposure and meteoric water leaching of the platform margin reef. Moreover, water?rock interaction in different types of dolomitization fluids was analyzed. Based on the analyses of the diagenetic environment of dolomite as well as dolomitization fluid properties and sources, combined with the hydrogeological model, the genesis of dolomite was studied. It is considered that the dolomicrite was formed by evaporating pump dolomitization during the penecontemporaneous period at near?surface with the dolomitization fluid of penecontem?poraneous high salinity evaporated seawater, while the biogenic dolomite and crystalline dolomite were formed by thermal convection dolomitization in the shallow to middle?buried diagenetic environments with the dolomitization fluid of synsedimentary high salinity evaporated seawater sealed in the stratum.

Key words: dolomite, reservoir characteristics, controlling factors, Loushanguan Group, southeastern Sichuan Basin

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