Oil & Gas Geology ›› 2018, Vol. 39 ›› Issue (2): 229-238.doi: 10.11743/ogg20180203

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Bedding decollement deformation domain in the Lower Paleozoic shales in Chongqing:Formation and geological significance

Yue Feng1,2, Li Yongchen3, Zhao Baoshan3, Zeng Xiangliang2   

  1. 1. Gansu Province Transportation Planning, Survey & Design Institute Co., Ltd., Lanzhou, Gansu 730030, China;
    2. Chongqing Institute of Geology and Mineral Resources, Chongqing 400042, China;
    3. PetroChina Coalbed Methane Co., Ltd., Beijing 100028, China
  • Received:2017-02-06 Revised:2018-03-12 Online:2018-04-28 Published:2018-05-16

Abstract: The study presents the types,characteristics and the forming process of the bedding decollement deformation domain in the Lower Paleozoic shales in southeast Chongqing via mechanical analysis based on the observation of shale outcrops and cores,and discusses its geological significances in combination with shale gas exploration practices.Two types of bedding decollement deformation domains,namely compression-type and gravity-type,are recognized.The compression-type is formed when horizontal compressive tectonic stress dominates and shale layers are under the action of reverse fault;on the contrary,the gravity-type is formed when the overburden pressure dominates and the shale layers are under the action of normal fault.Compared with the gravity-type,the compression-type is more intense in stratum deformation with larger scale of influence on shales.Burial depth and dip angles are the key geological factors that control the formation of bedding decollement deformation domain in the same shale layer in a certain area.The critical dip angles for the compression-type expand gradually with the shale burial depth increasing,whereas that for the gravity-type decreases gradually with the increasing burial depth.The gravity-type is destructive to the preservation of shale gas.The bedding crushed zones and net fracture systems resulted by compression-type in an anticline are interpreted as the main migration pathways and reservoir space for shale gas,while those in an syncline are the main pathways for shale gas migrating to adjacent anticlines or releasing in the atmosphere.

Key words: bedding decollement deformation domain, formation mechanism, geological significance, Lower Paleozoic, shale, Chongqing

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