| Recently,people concentrate more on prospection of shale gas,the areas of Sichuan,Chongqing and Guizhou become the main exploitative places of shale gas.This thesis concentrate on the tectonic features of the shale and perservation conditions of the shale gas of Wufeng-Longmaxi formations of Lower Palaeozoic Erathem in the southeast areas of Chongqing,and rudimentarily forcast the profitable areas of preservation,supplying the datas for advanced protection in Wufeng-Longmaxi formations.Initially,we observed six section planes in the field and rock cores of4wells. Then,combining the datas with the analysis of the background of regional structure, we generally expound the structural characteristics of shale of Wufeng-Longmaxi Formation and the preservation conditions of shale gas of Wufeng-Longmaxi Formation in southeast area of Chongqing.Our researches reveal that southeast area of Chongqing has been affected by multiple phases,including Caledonian movement,Indo-china movement,Yanshan movement, Himalayan movement,and etc.The main stuctural deformation behaviours in that area is compression deformation,including strike slip motions. Thus,its folds and rift structures have well developed.The main extending orientations of folds are North East and North North East,and the majority of folds axial surface dipping is South East.In terms of northwest to southeast,there are ejective folds,castellatus folds and trough-like folds,respectively.Southeast of Chongqing has four kinds of fault systems which contain North East,North North East,North West and North south.The main faults are North East and North West,and the angles of dip are always large.The main tectonic fractures of the southeast areas of Chongqing are shear fracture,gash-shear fractures and slip fracture.Prevalent directions are NorthEast,which angle of dip is small.Obeserving the rock cores for the length,width,angle of dip and so on,we can conclude that the longer the fracture,the smaller the width,the bigger the angle of dip.Tectonic actions control the development of fractures.Tectonic fractures always accompany with folds and fractures,and the developments of fractures are ofen connected with thickness of formation,the thinner the formation,the smaller the distance of fracture.The preservation conditions of shale gas are affected by thickness,cap rock,top buttom fearure,tectonic movement and structural styles.The north of shale formation of Wufeng-Longmaxi formation in southeast area of Chongqing is thicker than other directions,while east,west and south are thin. The upper regional cap formation in region of interest have developed well.Mudstone of middle-lower Permian of Silurian and mudstone and plaster rock of middle-lower Triassic of Silurian are both can be the effective regional cap formation in the region of interest. The upper regional cap formation of shale of Wufeng-Longmaxi formation in southeast area of Chongqing has developed well.Even if the areas of anticline have been seriously denuded,but Trias formation in areas of syncline has well preserved,which can be served as the regional cap formation.Luoreping formation covers Longmaxi formation directly, which contains a series of siltstone and silty sandstone,no cracks growing, which can be served as good roofs of Longmaxi formation.And below that are Baota formation or Linxiang formation,which is a series of nudolar shaly limestone, with stiff texture,can be served as good baseplate. The Structure movement of southeast area of Chongqing in Yanshan period is intense,resulting in serious deformation of whole area, sharp formation and well developed cracks.The areas which have good presavation of shale gas are always the palces have week tectonic movement.Basing on the structure characteristics and evaluation index to preservation condition of t he above-mentioned studied area. Six firstly favorable areas in the northwest of Wulong and ten secondary favorable areas in the west of Qianjiang were selected. |
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