Structural Evolution And Its Control On Accumulation Of Shale Gas In Jiaoshiba Area

Jiaoshiba shale gas field is the first shale gas field to realize commercial development in China.It is great significance for further exploration and development of other marine shale gas in China,by studying the tectonic development characteristics,evolution regularity,shale gas geological characteristics,the control action on shale gas accumulation of tectonic evolution and the structure preservation mode of Jiaoshiba systematically.Based on the full study of the regional geological structure background,this paper makes a comprehensive study on the geometric characteristics,kinematic characteristics and evolution process of the Jiaoshiba by using the traditional geological survey method,combined with the theory of indoor tectonics and simulation software,And the control of geological structure evolution to shale gas formation process is comprehensively studied.Mainly get the following understanding:The anticline of the Jiaoshiba is mainly controlled by NE,NW and near SN to the three groups of reverse faults,and the eastern and southern strata are obviously damaged by the faults.The surface joints are mainly NWW,NE and SN.The microstructure and rock structure reflect NW-SE and NE-SW~NNE-SSW to the multi-directional extrusion process.85Ma-65Ma(Yanshan movement late)is a strong transformation period.The total amount of strata is 3.8km and the shortening rate is 16.7%.Controled by the Dabashan orogen and the Jiangnan-Xuefengshan orogen,the history of tectonic evolution can be divided into five periods: the Caledonian period,The deposition of organic-rich shale of Wufeng-Longmaxi Formation,and the strata were uplifted and eroded at the end of the Silurian,and no wrinkles occurred in the area.Hercynian to the early Indosinian,The strata is sinking continuously.Indosinian early period,the conversion of marine facies to continental sediments,and the tectonic deformation of the Jiaoshiba is weak.Late Indosinian to early Yanshannian,the NNW-SSE squeeze is extruded to form a series of NE-trending faults.Late Yanshanian to early Himalayan is the main period that the NE-trending boundary fault of Jiaoshiba is formed.The squeeze direction is NNW-SSE~NWW-SEE;Late Himalayan,The squeeze direction is NE-SW,and the Wujiang fault system are mainly formed in this period.The thickness of mud shale of Wufeng-Longtaxi Formation is mainly in the range of 70 ~ 100 meter and the depth range is 2250 ~ 5000 meter.The law of buried depth is shallow in the east and the buried depth is deep in the west.The buried depth of the middle part is relatively shallow,distributed in the 2250 ~ 3000 meter.The mud shale has a high degree of thermal evolution of the shale organic matter in the area,and the mud shale of the Wufeng-Longmaxi Formation has experienced four stages of the lifting effect :late Caledonian,Late Hercynian,Early Indosinian and Late Yanshanian-Himalayan.Organic matter mature hydrocarbon generation has gone through the whole stage of immature to mature,completed from a small amount of hydrocarbon generation to dry gas generation of the whole process.The rapid uplift of late Yanshanian terminates the process of hydrocarbon generation of shale organic matter and re-adjusts or destroys shale gas reservoirs.The shale rock reservoir has the advantages of low tectonic transformation time,weak tectonic transformation intensity,closed fault development and The total gas content is distributed in the range of 5.8 ~ 6.7m3/ t.In the range of 2250 ~ 5000 meter of Jiaoshiba,the shale gas is dominated by free gas,Accounting for about 70% of the total gas content.