Reservoir Characteristics And Favorable Area Prediction Of The Lower Cambrian Niutitang Shale In Block1of Fenggang,Guizhou

China's southern marine shale gas resource potential is tremendous,which is the main battlefield of the shale gas exploration.Fenggang Block I which is located in the northern area of Guizhou Province,developed in organic-rich shale of Niutitang Formation of Lower Cambrian Series.This paper uses a new well of Fenggang Block I in Guizhou Province,called Well Yongxin 1 as an object of study.It adopted the test methods of organic carbon determination,vitrinite reflectance,kerogen maceral and type to analyze the organic geochemical characteristics of shale reservoirs;used slice,petrofabric measure,X-ray diffraction and clay mineral analysis to research the characteristics of rock mineral composition of shale reservoir;utilized scanning electron microscopy,argon ion polishing-field emission microscopy experiments and technology to divide the reservoir space of the marine shale reservoirs in the study area,pointing out the effects of different types of reservoir space for shale gas formation;applied the methods of nitrogen adsorption,porosity and permeability testing,experimental adsorption isotherm to analyze shale pore structure,pore size distribution,reservoir properties and adsorption characteristics;combined the observation and description of core and logging information to study the characteristics and the extent of shale reservoir fracture development.The thinking of combination of theoretical analysis and applied research is used to comprehensively study of the geologic feature of shale reservoirs and the controlling factors for shale pore structure,fractures,and other aspects of properties have been discussed.Finally,the evaluation standard of high quality marine shale reservoir had been summarized,and selected the favorable play of Cambrian Niutitang Formation shale gas preservation in Fenggang Block I.The results of comprehensive analysis are as below:In the study area,Niutitang Cambrian sedimentary period witnessed massive transgression and its sedimentary facies are mainly deep water shelf,semi-deep water shelf and shallow shelf.The thickness of the shale reservoir from Niutitang formation becomes thinner from northwest to southeast.The organic matter type of the target shale is mainly type?₁,which has high TOC content and maturity,and has excellent capacity of generating gas.Shale from Niutitang formation has high content of quartz mineral with high brittleness,and in which the average content of clay is 31.5%,in line with the characteristic of high quality shale-"high brittleness,low clay".Reservoir pore space can be divided into organic,inorganic holes and fractures.The pores in the shale reservoir are mainly composed of primary pores,intercrystalline pores of clay minerals and intergranular pores of pyrite.The pores of organic matter are not developed,and a certain amount of microcracks are observed.Shale reservoir porosity and permeability is very low,with a variety of pore structure types and mesoporous(2-50nm)is the main adsorption sites and reservoir space of shale gas.TOC,maturity and mineral components on the nanoscale pores of shale reservoir development has control action.The average gas adsorption of Niutitang black shale formation is3.79m³/t,and the shale has a high adsorption capacity.The fractures in the core of shale of Niutitang Formation from 2008 to 2022m in Well Yongxin 1 are well developed.According to the evaluation standard of high quality marine shale,the shale of 1993?2030m from Niutitang Formation is divided into favorable shale reservoir in Well Yongxin 1.In addition,the favorable area?in shale reservoir is mainly located in Tu Xi town–Xin Jian township area,shiping township area and the southwest of the researched area.The favorable area?is mainly located in the Tu Ping synclinorium in the west of researched area and the eastern Tujia'ao-Dejiang synclinorium and Anjiazhai anticline.