The Geological Model And Favorable Exploration Zones Of Shale Gas In Niutitang Formation,Lower Cambrian,Eastern Margin Area Of Sichuan Basin

The Niutitang Formation shale in Sichuan Basin has the characteristics of high organic matter maturity,complicated structure and strong late-reformation,and is a hot spot in China's petroleum industry.How to assess the shale gas resources is the difficulty and focus work for Niutitang Formation shale gas exploration and development.Based on detailed investigation of related literatures,experimental testing and data statistical analysis and so on,sedimentary environment,geochemistry,mineral compositions,reservoir and gas contant characteristics on organic rich shales in Niutitang Formation were studied in this paper.Then,nitrogen source and its accumulation mechanism were established.Finally,the favored exploration zones were selected using the methods of multi-factor superposition.?1?The Niutitang shale was deposited in deep retention shelf sedimentary environment,with the characteristics of high organic richness,high silica content,and high thickness with the average value 80 meter,which make it the excellent conditions for shale gas accumulation.The kerogen is mainly humic type which has the trend of gas generation.The organic richness is high but affected by sedimentary environments.The thermal maturity of shales mainly belongs to high or over maturation level.Mineral composition of the shales is mainly high fragile mineral contents such as quartz and feldspar,low clay minerals contents,and the clay minerals is mainly illite and illite mixed layer.The pores in shale are dominated by organic pores,interparticle pores,intraparticle pores,dissolution pores,and intergranular pores,with micropore and moderate pore predominant.?2?The total gas content of Niutitang shales is low,generally between 0.2 cubic meter per ton and 1.0 cubic meter per ton,and is relatively high content of nitrogen.The origin of shale gas is oil-type cracking gas.Nitrogen isotope and rare gas isotopic analysis indicated that the main sources of N₂ in the reservoir were the organic matter thermal decomposition,the mantle,and the atmosphere.The organic carbon content,specific surface area,quartz content and clay content are the main factors that had influences on shale gas contents.Through the multiple linear regression of the main control factors of the gas content,the formula of the gas content calculation is established.?3?Through the study of regional tectonic evolution and style,regional hydrogeology and caprock preservation conditions,the structural styles and the gypsum salt rock of Middle-upper Cambrian has an important significance in sealing and preservation of Niutitang shale gas.Further,it summarizes the geological model of gas content in the structure style of thrust,thrust block structure and thrust fold structure.?4?Base on organic carbon content,thermal maturity,thickness,depth,gas content and preservation condition,the favorable exploration zones of shale gas were selected with superimposed method.The favorable exploration zones were Weiyuan-Neijiang-Fushun,Suiyang-Zhengan-Wuchaun,Fenggang-Dejiang,Longshan-Laifeng-Hefeng,and Wanyuan-Chengkou for Niutitang shale gas.The papers focused on the shale gas accumulation conditions and offered a shale gas study for somewhere the shale in high-post maturity stage,which showed the excellent shale gas prospect of the plate edge.The study can guide shale gas exploration direction in Sichuan Basin,and has certain guiding significance for Niutitang Formation shale gas exploration practice in Sichuan Basin and even in south China areas.