Abstract:

Because of the previous researches on occurrences of shale gas and the influencing factors of gas-bearing property being insufficient,combined with shale microstructure characteristics,pyrolysis simulation experiments on enrichment capacity of hydrocarbon gas have been systematically carried out with different types of shale at different mature stages,under different lithostatic pressure and fluid pressure and with different geological characteristics.It indicates that the extracted gas amount in shale,being relatively large,is closely related to their thermal maturity,namely the extracted gas productivity is very large at over-mature stage.The percentage of extracted gas with siliceous shale is the highest,calcareous shale is the second,while argillaceous shale is the lowest.For the same type of shale,the percentage of extracted gas is the highest at mature stage,which is intermediate at high-mature stage and the lowest at over-mature stage.Over pressure can obviously enhance the extracted gas productivity of shale.The bigger the over pressure coefficient,the higher the productivity of extracted gas.In the case of the same thermal maturity and evolution process of shale,the extracted gas production in the normal depth of shale is obviously higher than that in uplifted shale.The greater the burial depth,the higher the extracted gas yield of shale.Siliceous and calcareous shale possess high contents of brittle mineral,with big pore and fracture.Their porosity is relatively big,so the extracted gas capability is strong.While argillaceous shale has relatively low contents of brittle mineral,mainly developing micropore during hydrocarbon generation process and there is no big fracture,resulting relatively small porosity.Therefore,the extracted gas capability is weaker than that of siliceous and calcareous shale.The residual gas yields of shale are very low,and basically it does not have industrial exploitation potential,so the amount of field desorbed and lost gas is key in shale gas content determination.The gas-bearing property of shale is jointly controlled by organic matter content and the reservoir physical property.Overpressure is the key of high production of shale gas,and shale gas enrich in dark and dark grey shale with calcareous (lime),siliceous and sandy thin layer (interlayer),developing better foliation.

Key words: Different types of shale, Pyrolysis simulation, Extracted gas, Main controlling factors for shale gas, Microstructure