Formation Conditions And Favorable Area Prediction Of Shale Gas In The Longmaxi Formation In Southern Sichuan

In this paper,the structural geology,sedimentary petrology,petroleum geology and other related disciplines as theoretical guidance,through core observation,logging interpretation,the test analysis and the existing research results of Longmaxi shale in southern Sichuan Basin,analyze and discuss the characteristic of the shale gas development in the Longmaxi Formation of the lower Silurian in southern Sichuan by regional distribution,organic geochemical characteristics,reservoir characteristics,gas concentration and preservation conditions.According to the main controlling factors of shale gas enrichment at home and abroad,combining with the geological conditions in the study area,analyze the evaluation index of shale gas enrichment region,and finally predict favorable exploration areas of shale gas in southern Sichuan Basin.The thesis mainly made the following results and understanding.The study area is located in the southwest Sichuan Basin,it mainly includes the palaeohigh tectonic belt in southwest Sichuan and lowly anticline tectonic belt in southern Sichuan.Because of palaeohighs in the middle of Sichuan and Guizhou,it develops relatively closed and hypoxia shelf sedimentary facies which consists of carbonaceous shale,arenaceous shale,argillaceous sandstone,etc.In study area,the thickness of organic-rich shale is in the range of 10?80m,the largest sedimentary area which is Fushun-Luxian region can reach above 70m.The shale buried depth between 1000?7000m and Weiyuan area,Changning construction,Luzhou and Jiangjing is less than 3500m.It contains high amout of organic matter with total organic carbon(TOC)content between 0.04%and 8.09%,the average is 1.83%.The average ?13C value of kerogen is-29.8‰ and the maceral is given priority to sapropel group,so the shale have mainly type I kerogen.The thermal maturity rech high-to-over mature stages which have a high degree of thermal evolution between 1.84?4.21%and the average is 2.47%.The mineral composition are mainly quartz,feldspar,calcite,dolomite,clay minerals and pyrite,the average silica content(quartz and feldspar)is 40.05%,Brittleness minerals content is high and the clay minerals content is relatively low.The shale has good reservoir property with a high porosity(average of 4.02%)and the permeability are mainly distributed in 0.00001?0.0001mD.Shale gas in reservoir is mainly stored in organic micropores,interlayer micropores in clay mineral and a large amount of microfractures.The gas content in reservoir is high,average of 2.54m3/t.In conclusion,based on the research of Longmaxi shale gas forming conditions and preservation conditions in southern Sichuan,according to shale gas evaluation index,by using the method of superposition of multiple factors,predict favorable exploration areas of shale gas in the Longmaxi Formation of the lower Silurian in southern Sichuan by buried depth,the thickness of organic-rich shale,organic geochemical characteristics,reservoir physical properties and the brittle mineral.Comprehensive analysis think that the shale gas favorable exploration area are include Weiyuan,Suijiang-Junlian-Gongxian,Luzhou and Jiangjing 4 regions,among of them the first two larger areas are key exploration area.