摘要
The Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin is located in the complex marine tectonic area of South China,where shale deformation and reformation are intense and the factors controlling sweet spots are complex,so the preservation conditions have an important impact on the enrichment of shale gas.In order to support the selection and evaluation of shale gas sweet spots in this area and improve the success rate of drilling,this paper carried out a geological survey onfield outcrops.Then,based on drilling,mud logging and physical property test data,the structural deformation pattern and the regional deformation characteristics of this demonstration area were analyzed,and the development characteristics of formation joints and fractures,the sealing capacity of shale sur-rounding rock and the distribution characteristics of gas reservoirs were studied.Finally,the preservation conditions of shale gas in the Wufeng Formation of Upper Ordovician and the Longmaxi Formation of Lower Silurian were discussed.And the following research results were ob-tained.First,in the Zhaotong National Shale Gas Demonstration Area,three structural deformation patterns are developed from south to north,including trough type,equal amplitude type and baffle type,which are distributed in three major deformation zones,respectively,i.e.,the shear deformation zone of Central Guizhou Uplift,the compressionetorsion deformation zone of northern YunnaneGuizhou Depression and the compression deformation zone of Southern Sichuan Depression.Second,three types of joints and fractures whose relationships with the di-rection of strata are high angle,middleelow angle and bedding intersection are developed in the WufengeLongmaxi formations and its overlying strata,and their occurrence characteristics are basically consistent with those of the three major deformation zones.Third,the shale of WufengeLongmaxi formations is thick in the north and thin in the south and possesses the preservation conditions of sourceereservoir inte-gration and self-sealing hydrocarbon accumulation.And combined with the sealing ability of the overburden strata and the roof andfloor,its preservation conditions are overall better.Fourth,from the perspective of shale gas component,this area can be divided into three belts,i.e.,methane,methaneþnitrogen mixture and nitrogen from north to south.And the preservation conditions of shale gas are generally better in the north and worse in the south.In conclusion,the shale in the centralenorthern part of Zhaotong National Shale Gas Demonstration Area(compression deformation area and its southern margin)is the most favorable area because of its large shale thickness,weak reformation and deformation,bedding development of joints and fractures,good sealing performance and excellent preservation conditions.The compressionetorsion deformation zone of northern YunnaneGuizhou Depression in the central part is moderate in preservation conditions,and it is the relatively favorable area.The shear deformation zone of Central Guizhou Uplift in the southern part has poor preservation conditions,and it is a prospective area.
基金
supported by the National Major Science and Technology Project"Zhaotong Shale Gas Exploration&Development Demonstration Project"(No.2017ZX05063)
CNPC Major Field Test Project"Research and Test of Key Effective Expoitation Techniques of Deep Shale Gas"(No.:2019F-13)。
