Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (2): 335-345.doi: 10.11743/ogg20190212

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Characterization of braided river reservoir architecture of the Upper Paleozoic He 8 member on Fugu Tianshengqiao outcrop,eastern Ordos Basin

Chen Dongyang1,2, Wang Feng1,2, Chen Hongde1,2, Wei Xinshan3, Sun Shi1,2, Zhu Shengxian1,2   

  1. 1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    2. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    3. Research Institute of Exploration and Development of Changqing Oilfield Branch Company, PetroChina, Xi'an, Shaanxi 710021, China
  • Received:2018-05-11 Revised:2018-12-03 Online:2019-04-28 Published:2019-01-23

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Abstract: The major gas pay zone lies in the 8th member of the Upper Paleozoic Lower Shihezi Formation(He 8 member),eastern part of Sulige region,Ordos basin.Its reservoir architecture acts as a predominant geological factor for oil/gas distribution.Targeting at Tianshengqiao outcrop in Fugu county in eastern Ordos Basin,similar to eastern Sulige region in provenance and sedimentary setting,we finely studied the architecture of the outcropped sand body,which can offer critical information for the establishment of geological model of eastern Sulige region.Based on the outcrop survey,pe-trographic investigation,architecture analysis and fine measurement of sand body volume,combined with the sedimentary and petrologic analyses,we recognized twelve types of lithofacies in the braided river deposits of He 8 member.Six levels of architecture interfaces were classified within the reservoirs,namely composite channel-belt,single channel-belt,single sand body,silty layer accompanied with accretion,bed set,single bed and laminae.Six reservoir architecture units are indentified,that is,channel filling(CH),longitudinal bar(LB),diagonal bar(DB),transverse bar(TB),abandoned channel(ACH) and overflow deposits(OF).Among these,sand bar is a dominant reservoir architecture unit.The thickness of longitudinal bar ranges between 2.5m and 5.8m with the width/thickness ratio varying from 27.6 to 37.7; the thickness of diagonal bar ranges between 2.2m and 6m with a width/thickness ratio varying from 38.4 to 42.1; while the thickness of transverse bar ranges between 1.5m and 3.6m with a width/thickness ratio varying from 47.0 to 61.8.Based on the analyses of different architecture units,we summed up the spatial superimposition patterns of the reservoir,established the 3D architecture model of braided river composite sand body in the He 8 member of Tianshengqiao outcrop in Fugu county,both of which will provide geological evidences in the fine description of He 8 member in eastern Sulige region.

Key words: braided river, architecture interface, reservoir architecture, Lower Shihezi Formation, Tianshengqiao outcrop, Ordos Basin

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