Tectonic Deformation Characteristics And Its Effect On Shale Gas Enrichment And Preservation Of The Fuling Region

The Fuling area,the most important shale gas exploration and development area in the Sichuan Basin,has undergone multi-stage complex structural superimposed deformation.The Fuling area has a structural architecture with east-west zonation and south-north subsection on the plane.Longitudinally,affected by three sets of detachment zones,The Fuling area is subdivided into four structural deformation zones,and the deformation of the lower structural layer is relatively strong.According to the intensity of structural deformation and the characteristics of faults and cracks development in the study area,The Fuling area is subdivided into four types and eleven zones,including:(1)strong thrust structural deformation zones: the Baima syncline thrust belt,the Shimen-Jinping anticline thrust belt;(2)structural transition deformation zone: the Wujiang anticline belt;(3)fault fold deformation zones: the Fuling syncline belt,the Zilichang anticline belt,the Jiangdong syncline belt,the Baitao syncline belt,the Pingqiao anticline belt and the Shuanghekou syncline belt;(4)gentle structural deformation zones: the Jiaoshiba anticline belt and the Fengliai syncline belt.There are two fault systems,NE and NW trends,are developed in the Fuling area,which are shown to be the product of two different compression processes by the results of plane physical simulation.The first compression period is from the end of late Jurassic to the beginning of early Cretaceous,the motive force come from the remote effect of the westwards subduction of the Pacific plate and the upwelling of deep magma in the Xuefengshan tectonic belt form NE-trending structures.The second stage of compression was in the early stage of Late Cretaceous.The thrust of the Daba Mountain from NE to SW combined with the continuous compression of the Xuefeng intracontinental orogenic belt to NW resulted in nearly EW-trending superimposed stress in the Fuling area,forming nearly SN-trending structures.The intensity of structural deformation is an important factor affecting the enrichment and preservation of shale gas.Large-scale faults can produce damage zones of a certain width,so strong thrust zones and structural transition zones have the worst gas content;wide and gentle anticlines,fault anticlines or gentle synclines have weak structural deformation,and faults do not develop.At the same time,strata with weak uplift and denudation are most conducive to shale gas preservation;affected by the main faults,cross-layer fractures and along-layer fractures are not conducive to shale gas preservation.