Oil & Gas Geology ›› 2016, Vol. 37 ›› Issue (3): 332-340.doi: 10.11743/ogg20160305

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Sedimentary characteristics of braided river delta of the lower member of the Lower Ganchaigou Formation in southwestern Qaidam Basin

Tan Xianfeng1,2, Xia Minquan1,2, Zhang Qingxue3, Wang Jia1,2, Huang Jianhong3, Ran Tian1,2   

  1. 1. Chongqing Key Laboratory of Complex Oil and Gas Exploration and Development, Chongqing 401331, China;
    2. School of Petroleum Engineering, Chongqing University of Science and Technology, Chongqing 401331, China;
    3. Research Institute of Petroleum Exploration and Development, PetroChina Qinghai Oilfield Company, Dunhuang, Gansu 736202, China
  • Received:2015-11-23 Revised:2016-03-02 Online:2016-06-08 Published:2016-06-22

Abstract: A braided river delta deposited at the lower member of the Lower Ganchaigou Formation in the Kunbei step-fault zone of southwestern Qaidam basin is considered to be of great importance to the study of oil and gas accumulation in the region.Analyses based on drilling core,logging and seismic data,as well as grain size statistics,were employed to perform a detailed study on the sedimentary characteristics of the delta.Three subfacies were recognized in the delta:braided-river delta plain,braided-river delta front and prodelta.The plain subfacies can be further divided into two micro-facies:braided channels and flood plain.The front subfacies can be subdivided into five micro-facies:under water distributary channel,mouth bar/distal bar,sheet sand and under water distributary bay.Vertically,the delta evolved successively from braided river delta plain,braided delta front to shore-shallow lake. The plain facies experienced superimposition of multiple channels,while the front facies had only a weak influence over the channels.Horizontally,it was controlled by two major provenances and developed two main channels with horizontal heterogeneity.The syngenetic faults were consi-dered as the major controlling factors upon the development of the delta,while the provenance constraints were thought to have affected the distribution and composition of the delta sandbodies and the paleogeomorphology helped forming the present landform of the delta.A sedimentary model was then established for the delta based on comprehensive analyses of all geological factors.

Key words: braided river delta, sedimentary facies, sedimentary model, Lower Ganchaigou Formation, Kunbei step-fault zone, Qaidam Basin

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