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Geoscience ›› 2018, Vol. 32 ›› Issue (02): 364-373.DOI: 10.19657/j.geoscience.1000-8527.2018.02.15

• Petroleum Geology • Previous Articles     Next Articles

Detailed Study of Lake Fine Grained Deposition Characteristics: A Case Study from Chang 7 of Yanhe Section, Ordos Basin

LÜ Qiqi1,2(), LUO Shunshe1,2(), FU Jinhua3,4, NIU Xiaobing3,4, XU Liming3,4, FENG Shengbin3,4, LI Shixiang3,4   

  1. 1. Laboratory of Exploration Technologies for Oil and Gas Resources (Yangtze University), Ministry of Education,Wuhan, Hubei 430100, China
    2. Hubei Cooperative Innovation Center of Unconventional Oil and Gas (Yangtze University), Wuhan, Hubei 430100, China
    3. National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields, Xi’an, Shaanxi 710018, China
    4. PetroChina Changqing Oilfield Company, Xi’an, Shaanxi 710018, China
  • Received:2017-05-11 Revised:2017-11-04 Online:2018-04-10 Published:2018-05-07

Abstract:

Field geological outcrops play a significant role in meticulous depiction of the internal structure of sedimentary deposits and establishing accurate underground geological model. This paper takes Chang 7 of Yanhe outcrop section in Ordos basin for instance, adopts the methods of petrology and field outcrop sedimentology, and detailedly analyses the lithofacies type, characteristies, vertical combination and sedimentary environment of lake fine grained sediments. The results show that Chang 7 of Yanhe outcrop section develops 9 types of lithofacies, including parallel bedding fine sandstone facies, flowing water crossbedding fine sandstone facies, wave forming crossbedding fine sandstone facies, ripple cross lamination siltstone facies, deformation bedding siltstone facies, horizontal bedding(argillaceous )siltstone facies, bulk mudstone facies, horizontal bedding(sandy)mudstone facies, big wavy-straight laminae shale facies. On the basis of combining regional geological characteristics, this paper regards the Chang 7 as distal sources meandering stream deltaic front and shallow-semi-deep lake sedimentary, further divided into 7 categories sedimentary units, among which underwater distributary channel and bar between branches developed well, subsea natural barrier, distal bar and sheet sand developed small scale, shallow-semi deep lake sedimentary only developed at the lower part of the Chang 72 subsegment, mouth bar developed hardly, only partial visible. Thorough research on the vertical distribution characteristics of every sedimentary unit, 4 vertical distribution forms of Ⅰ,Ⅱ, Ⅲ, Ⅳ are recognized. Ⅰ、Ⅱ combination mainly distributed at the research area Chang 71 and Chang 73 subsegments. Ⅲ、Ⅳ combination mainly distributed at the research area Chang 72 subsegments. Section facies analysis shows that during integral Chang 7 deposition period, a fine grained sedimentary sequence of thin to coarse was formed, showing meandering stream deltaic front sedimentary-shallow lake-semi-deep lake sedimentary-meanderiing stream deltaic front sedimentary.

Key words: fine grained sedimentary, sedimentary outcrop, lithofacies type, vertical combination, Chang 7, Ordos basin

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