Study Of Shale Characteristic And Containing Gas Potential Of The Permain Longtan Formation In Lower Yangtze Region,China

The paper studied by a main line of geological background of organic-rich shale reservoir-forming conditions,shale macro and micro characteristics,main controlling factors of gas content,and strategic select potential areas of shale gas reservoir development.Geological analogy method is used on the discussion of containing gas potential of shale gas in the Permian Longtan formation of the Lower Yangtze region,and used comprehensive information superposition method to predict initially the favorable areas for shale gas reservoirs.The conclusions are as follows:(1)Lower Yangtze basin had undergone three phase reform in tectonic evolution,just as smooth settlement,thrust nappes and tensile depression.The layer of Late Permianepoch system black shale was controlled by the deposits of the transitional nature from marine to continental facies,Among which longtan formation,which belong to shoreland swomp-delta facies,mainly develop interlayer of gray-black mudstone,carbonaceous shale,gray fine sandstone and pelitic siltstone,between which coal seam deposited.(2)There is a wide range of erosion of Longtan formation in the northwest and southwest in study area,the rest area are all buried deeply;The burial depth of central region of Suzhou-Wuhu is 200-1000m,buried moderately;The dark mud shale sedimentary center in south region of Lower Yangtze is located in GuangDe and YangZhong area,whose thickness is larger than 150m,and thickness of mud shale round them decreases in radial pattern.(3)The total organic carbon type mainly dominated kerogen typelll,containing also a small amount of kerogen type ?b;the total organic carbon content of black shale of Longtan formation is higher,but changes in range is larger too,its variation range is 0.52%-8.17%,average 2.11%;Thermal evolution of organic matter has different levels,its general variation range is 0.66%-3.10%,average 1.40%,the most are in the stage of mature-high mature.(4)The fragile mineral average content of black shale(the main fragile mineral is quartz)is more than 40%,clay mineral average content is less than 50%,it is beneficial for both shale gas adsorption and reservoir fracturing;The pore types of reservoir is basically about intergranular pore and dissolving pores,the permeability of most black shale are less than 1md,porosity mainly distributes between 0.12%and 4.20%,suggesting that the shale in the whole study area has good reservoir conditions.(5)The result of isothermal adsorption simulate test showed that,the adsorption capacity of Longtan formation of black shale is much stronger,the gas content mainly distribute between 0.78m3/t and 1.34m3/t.The regional cap distributed widely,preservation conditions in study area is relatively good.To a certain extent,there is exploration prospects of shale gas.(6)The controlling factors of shale gas accumulation include the total organic carbon type and abundances,maturity,fragile mineral content,clay mineral content,porosity,gas content,etc,which have an important influence of shale gas accumulation;(7)Initially establish the forecast model and parameter selection criteria of shale gas development block(potential areas and favorable area).The favorable areas for developing shale gas reservoirs of target strata is forecast by comprehensive information superposition method.By synthesize analyse,there are two favorable areas of developing shale gas reservoirs,one is Lishui-Yangzhong,the other is Suyang.both of them own great stacking thickness,higher maturity,suitable burial depth,relatively good preservation conditions,and have very good accumulation conditions and exploration prospect for shale gas.