Fracture-Seepage Evolution Law By Carbon Dioxide Phase Change Blasting In Low Permeability Coal Seam

In view of the problem of single low permeability and high gas seam mining,carbon dioxide phase change blasting is adopted to increase the permeability of coal,which is considered as an effective measure to realize the safe mining of coal body under this condition.It has been widely used in the field.However,the characteristics of impact stress produced by phase change blasting are different from those of traditional explosive blasting,and there are still some deficiencies in basic theoretical research.In order to determine the cracking mechanism of carbon dioxide phase change blasting and the permeability and seepage characteristics of fractured coal,the following studies are carried out:(1)The initiation mechanism of carbon dioxide phase change blasting is analyzed.Based on the analysis of the physical properties of carbon dioxide in phase change blasting,the energy equation is determined and the influences such as volume and pressure are analyzed.The stress characteristics of borehole under blasting impact stress and the fracture mechanism of surrounding medium under stress wave and unloading carrier wave are analyzed.(2)The crack evolution law of carbon dioxide phase change blasting was determined.The crack characteristics and propagation mechanism of phase change blasting are determined by numerical simulation method.Multiple cracks and main cracks are formed in coal body by phase change blasting,and the cracks are mainly affected by tensile stress around boreholes by phase change blasting.At the same time,the fractal method is used to compare the damage and failure characteristics of coal mass caused by different fracturing modes.(3)The permeability-enhancing gas seepage characteristics of fractured coal are studied.Based on the fractured coal mass produced by phase change blasting,the process of permeability enhancement and gas permeation after fracturing is studied.The dominant channel of gas flow is formed by the coal fracture,and gas in coal flows to the nearest crack.Phase change blasting has a wide distribution of coal cracks,which can relieve pressure and increase permeability of the whole coal body.(4)The field application effect of carbon dioxide phase change blasting for cracking and permeability enhancement was tested.After phase change blasting was used in E2307 working face of Gaohe energy,many cracks were produced in coal body,which promoted gas analysis and flow.The gas extraction concentration of fracturing hole is increased from 15% to more than 50%,the permeability coefficient of coal body is increased by more than 10-20 times,which improves the efficiency of gas extraction and guarantees the safety of mine production.This thesis contains 55 figures,8 tables and 131 references.