Analysis Of Shale Gas Geology Characteristic And Gas Bearing In The Lower Cambrian Hetang Formation, Southern Anhui Province In Lower Yangtze Region, China

The paper is studied in the geological background of shale forming conditions in theHetang formation, organic geochemical characteristics of the shale, spatial extension andreservoir development characteristics of shale, main controlling factors of gas content, andpreserve condition of shale gas. Geological analogy method is used in the discussion ofcontaining gas potential of shale gas in the lower Cambrian Hetang formation of SouthernAnhui province, the Lower Yangtze region. The conclusions are as follows:(1) The blackshale of Hetang formation layer of Lower Cambrian system mainly developed interlayer ofsiliceous shale, siliceous stone, carbonaceous shale and carbonaceous mudstone. There is awide range of erosion of Hetang formation in the south in study area, the rest area are allburied deeply. The black mud shale sedimentary center of Hetang formation in studyregion is located in YiXian and NingGuo area, which effective thickness is larger than150m.(2) The total organic carbon type of black shale mainly dominated kerogen type I,containing also a small amount of kerogen type IIa；the total organic carbon content ofblack shale of Hetang formation is higher, but changes in range is larger too, its variationrange is0.14%-38.39%, average4.96%; Thermal evolution of organic matter has differentlevels, its general variation range is2.36%-4.53%, average4.31%, the most are in the stageof high mature-low metamorphic.(3) The fragile mineral average content of blackshale(the main fragile mineral is quartz) is more than50%, clay mineral average content isless than40%, it is beneficial for both shale gas adsorption and reservoir fracturing; Thepore types of reservoir is basically about intergranular pore and dissolving pores, thepermeability of most black shale are less than1md, porosity mainly distributes between0.03%and0.95%, so the shale in the whole study area has low reservoir conditions.(4)The result of isothermal adsorption simulate test showed the adsorption capacity of theblack shale of Hetang formation is much stronger, the gas content mainly distributebetween1.52m3/t and2.83m3/t. The regional cap distributed widely, preservationconditions in study area is relatively good. To a certain extent, there is explorationprospects of shale gas. With the strong tectonic movement and wide spread magmatic region, the preserve condition is important for gas content of black shale. Hetang formationis one set of high quality shale, but the black shale has lost hydrocarbon generationpotential and structural alteration of the latter had a decisive impact on shale gas reservoirsit during Indochina period.(5) The controlling factors of shale gas accumulation includethe total organic carbon type and abundances, maturity, fragile mineral content, claymineral content, porosity, gas content, etc, which has an important influence of shale gasaccumulation.