Sedimentary Microfacies And Sedimentary Environment Evolution Of The Black Shale Section Of Wufeng Formation-Longmaxi Formation In Changning Area

The Changning area is a nationally established national shale gas demonstration area.The black shale of the Wufeng Formation-Longmaxi Formation is the optimal stratum.In order to achieve the goal of building the southern Sichuan region into an important shale gas production base in China,it is urgent to accelerate the pace of shale gas exploration in the Wufeng Formation-Longmaxi Formation in this area,and carry out the petrographic assemblage of Wufeng Formation-Longmaxi Formation in the research area Basic research work on fine characterization of sedimentary facies and evolution of sedimentary environment.It can more accurately delineate the boundaries of facies belts that are conducive to the development of shale gas,study the shale sedimentary environment and organic matter enrichment organic matter,and provide scientific basis for further deepening the exploration and development of shale gas in this area.Based on many previous research results,this dissertation uses sedimentary theory as a guide,introduces the research methods of sedimentary microfacies,and uses drilling cores,test analysis,and logging data to develop the Wufeng Formation-Longmaxi Formation in Changning area.The fine characterization of shale lithofacies and sedimentary microfacies has reshaped the evolutionary process of sedimentary environment during the late Ordovician-Early Silurian Elonian deposition in the Changning area.The paper has achieved the following main results:(1)Based on the observations of cores and cast slabs in the study area,and analysis of the whole rock minerals,the black shale section of the Wufeng Formation-Longmaxi Formation is divided into 11 types of rock microfacies.Homogeneous siliceous shale,homogeneous calcareous siliceous shale,mean calcareous clayaceous shale,textured calcareous siliceous shale,textured silty shale,textured calcareous Argillaceous siltstone,biologically disturbed siltstone shale,carbonaceous shale,porphyry,pencil shale,radiolarian shale,crust bioclastic limestone.The black shale section of Wufeng Formation-Longmaxi Formation is divided into 11 types of rock microfacies: homogeneous siliceous shale,homogeneous calcareous siliceous shale,mean calcareous clayaceous shale,and stratified calcareous siliceous Shale,textured layered silty shale,textured layered calcareous muddy siltstone,biologically disturbed silty shale,carbonaceous shale,porphyry,penstone shale,radiolarian shale 3.Crustal limestone.(2)Based on the division of lithofacies and identification of sedimentary structures,the classification of microfacies and the evolution of microfacies in the Changning area are carried out through the combination of lithofacies,sedimentary structure,organic matter,paleontology,and logging facies With exhibition.The evolutionary sequence of the sedimentary microfacies during the Late Ordovician-Early Silurian Wufeng Formation-Longmaxi Formation in Changning area is platform-fat-deepwater facies organic calcareous silicon sheds-shallow facies crust shoals-deepwater facies organic-rich silicon sheds-deepwater facies Calcareous silicon shed-deepwater phase organic argillaceous silicon shed-deepwater phase organic-grade silicon mud shed-deepwater phase-depleted organic matter calcium-containing silty sand shed-deepwater phase-depleted organic argillaceous silty shed.The distribution characteristics of sedimentary microfacies in Changning area have good local ductility,large differences in sediment thickness,and the overall situation is inclined to the southeast to the northwest.(3)Based on the rock characteristics,paleontological characteristics,and chemical characteristics of the Changning area,research methods such as petrology,mineralogy,paleontology,and geochemistry were used to study the evolution of glacial events and volcanic activities.Glacier activity was identified in two episodes.Volcanic activity was mainly concentrated in the late Kaidi and early Ludanian stages.The evolution process of the sedimentary environment in the Late Ordovician-Early Silurian is: Late Cadyian-Early Hernant is a calm and strongly retained organic calcareous siliceous continental shed Middle Hernantian is a shoal shoal microfacies Late Hernant is a deep-water semi-stagnation hypoxia organic-rich silicon shed deposition in deep water Environment The early depositional environment of the Ludanian stage evolved into an underflow semi-retained hypoxic organic matter calcareous silicon shed in the deep water phase The underflow anaerobic-anoxic organic argillaceous silicon shed-siliceous shed shed in the late Ludanian stage The step environment has evolved into an underflow-weak turbid flow oxygen-enriched organic depleted silty silt shed.