Study On Heterogeneity And Alteration Ability Of Shale Gas Reservoir In Coal-bearing Of Hedong Coalfield

Shale gas resources is rich in transient phase in china(about 8.9×10¹² m³),mainly distributed in the coal-bearing shale.The significant heterogeneity in the macro and micro scales of the coal-bearing shale has a great influence on alteration ability.The shale reservious of Carboniferous Permian Taiyuan formation and Shanxi formation in Hedong Coalfield were taked as the research object,reservoir heterogeneity and transformation of characteristics were studied by means of borehole statistics,experimental testing and theoretical analysis,selected high quality layer and analyzed the mechanism of the influence of heterogeneity on alteration ability.The results as follows:Based on shale thickness and interlayer,the coal shale reservoir was divided into four layer?from top to bottom I and II,III and IV?,the thicknesses of them are26.79m,17.42m,11.13m and 25.32m,with coefficients of variation of 0.56,0.33,0.79,and 0.69,respectively.The mean depth of the bottom of Taiyuan formation is676 m.Organic matter type is III;TOC is 3.27%in average,with a coefficient of variation of 0.49 in average.Ro is 1.93%in average,at maturity and over maturity.The quartz content is 40.63%,with a coefficient of variation of 0.11 in average.The clay minerals content is 46.88%with a coefficient of variation of 0.16 in average.The specific surface area is 4.65 m²/g with a coefficient of variation of 0.43 in average.The total pore volum is 0.007 m L/g,with a coefficient of variation of 0.26 in average.The pore size is 20.25 nm,with a coefficient of variation of 0.44 in average.The porosity is 1.62%,with a coefficient of variation of 1.01 in average.The scope of permeability distribution between 0.019×10^-3 m D and 3.67×10^-3m D(0.331×10^-3 m D in average)with a coefficient of variation of 0¹.92?0.92 in average?.From top to bottom,the evaluation score based on the reservoir characteristics are Q₁=?0.69,0.48,0.31,0.58?and the evaluation score based on the reservoir heterogeneity are Q₂=?0.42,0.65,0.32,0.63?,Comprehensive evaluation score Q_c are0.55,0.57,0.32 and 0.60,respectively.The alteration ability based on mineral composition are 0.57,0.28,0.33,and 0.66 and the alteration ability based on rock mechanics are 0.55,0.50,0.49,and 0.34.Comprehensive alteration ability are 0.65,0.39,0.52 in respectively.The weaker heterogeneity of thickness,TOC and gas content,quartz content are,the stronger heterogeneity of the specific surface area,porosity,average pore size and permeability are,the more complex the hole cracks is,the more beneficial for fracturing.It is considered that the second section is the preferred fracturing section by combining the characteristics of macroscopic and microscopic characteristics with their heterogeneity.This paper have obtained the characteristics of the spatial distribution,reservoir geochemistry,physical property and reconstruction of shale gas reservoir in coal-bearing of Hedong Coalfield.and elaborated the characteristics of macro heterogeneity and micro heterogeneity of reservoir,then selected high quality layer.Revealed the microscopic mechanism of the influence of reservoir heterogeneity on alteration ability.The above results can provide the basis for the evaluation and development of shale gas reservoir in coal-bearing and the selection of high quality reservoirs layer.