Geological-engineering Sweet Spot Evaluation Of Shale Gas In Marine-continent Transitional Facies In Ordos Basin

The exploration of shale gas in marine-continent transitional facies in my country is in its infancy,and it is urgent to establish a criteria for the selection of geologic-engineering sweet spot,and to carry out the selection of favorable areas.Guided by sedimentology,petrology,petroleum geology and logging,this paper comprehensively analyzed the organic geochemical and gas-bearing characteristics of the Carboniferous-Permian shale in the Eastern Ordos Basin,then clarified the distribution characteristics of high-quality shale reservoirs,and calculated shale gas resources,finally established evaluation criteria for geologic-engineering sweet spot,and select favorable areas through geological survey,core observation,drilling,logging data and various experimental testing methods.The main results are as follows:(1)The Carboniferous-Permian shale in the Ordos Basin is 40-180 m thick,with an average thickness of 88 m,of which the shale in the Shanxi Formation is over 65 m thick,and it has stable distribution in the Eastern Ordos Basin.(2)Its gas-generating conditions are favorable.The TOC content of Shan 23 is 2.6%~12.0%,with an average of 6.8%.The kerogen type is mainly type II2,and the Ro is 2.4%~3.2%,which is in the dry gas stage.The measured gas content is 1.83 m3/t ~ 3.08m3/t,and the gas component is mainly methane.(3)Its reservoir conditions are relatively good,with a brittle mineral content of 50%-60%,mainly being quartz.The porosity is 2.6%~5.3%,mainly being inorganic pores,which are more conducive to fracturing.(4)For the first time,the volume method was used to calculate the shale gas resources of the Shan 23 of the Daning-Jixian Block,and the shale gas resources are 7332×108m3.(5)Optimizing shale thickness,gas content,TOC,brittleness index,and porosity as the establishing selection criteria for favorable geological areas,the Daji51 Well Area was selected as the geologic-engineering sweet spot,superimposed favorable engineering areas,and a pilot test area for shale gas in Marine-Continent Transitional Facies by Petrochina CBM.