| The research of reservoir characteristics,gas bearing formation test characteristics and recovery factor of resources are the core content in this article,the recoverable potential of coalbed methane resources in Muling depression is comprehensively evaluated through fine reservoir characterization,formation fluid reaction capture during fracturing and drainage and estimation of resource recovery factor.Through the research and analysis of the coal seam development characteristics,gas bearing characteristics,coal quality and metamorphic degree,reservoir physical properties,reservoir pressure,hydrogeological conditions and other reservoir characteristics in Muling depression,the main favorable CBM development section of Muling depression is located in the middle and lower part of Chengzihe Formation,the coal seam in this section has stable development,large coal thickness,moderate buried depth and concentrated coal seam distribution,the thickness of No.14 coal is 1.75-2.9m,the thickness of No.22 coal is 1.85m,and the gas content is 5.72-8.7m3/t,the permeability is 0.386m D,the gas saturation is greater than 56%,the critical desorption pressure is about 7MPa,the formation pressure coefficient is 1.09,the coalbed methane reservoir has good mining ability on the whole,but the permeability of coal seam is low,so it needs large scale reservoir reconstruction to improve the permeability of the reservoir.Through the fine comparative study of fluid characteristics and formation stress response in each stage of fracturing and drainage in gas bearing formation test,the fracture pressure of deep 22 coal seam is 40%higher than that of 14 coal seam,the fracture pressure of 22 coal seam is 39.85 MPa,and the fracture pressure of 14 coal seam is 28.42 MPa;the study of regional in-situ stress characteristics shows that horizontal complex fracture network is easy to be formed by fracturing,and the measured fracture extension is mainly in east-west direction,accompanied by southwest and northwest fractures developing,the fracture extends in the coal reservoir,the fracture height is controlled,and the pressure diffusion is fast after fracturing.The pressure drop rate of 22coal is 4KPa/min,and that of 14 coal is 2KPa/min.There are many free gas in 22 coal seam,and the temporary storage ratio of 14 coal seam is as high as 6.67.The middle and lower section of Chengzihe formation is the same pressure system without interlayer interference,so it is suitable for combined layer production process system;during the middle stage of drainage and production,the interruption of liquid drainage and the rise of flow pressure will cause great damage to the reservoir,it will reduce gas production by50%-70%and water production by 30%.The estimated CBM resource amount of Muling Depression is about 270.12×10~8m~3,among which the predicted resource amount is 110.72×10~8m~3 and the prospective resource amount is 159.39×10~8m~3.The coal bed gas resource controlled by a single well is about46.74×10~5m~3,the amount of coal geological resources of No.14 coal is about25.86×10~5m~3;the amount of coal geological resources of No.22 coal is about 20.88×10~5m~3.Comprehensive analysis of the calculation results of analogy method and isothermal adsorption method shows that the recovery rate of coalbed methane resources in Muling depression can reach 55%-65%. |
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