| Gas is a major hazard source in coal mines.How to efficiently utilize coal seam gas resources and effectively eliminate the threat of mine gas is of great significance.This thesis takes the 8406 working face of Yangquan Minmetals as the engineering background,and through testing the basic parameters of coal and gas in the working face,it is concluded that the pores of the No.15 coal seam are well developed,easy to absorb gas and have strong adsorption capacity.After analyzing the drilling layout and drainage effect,it is found that the gas content and gas pressure in some areas still exceed the safety critical value after the gas drainage.In order to ensure the safe mining of the mine and the normal replacement of the mining face,it is proposed to inject N2-O2 mixed gas Displacement coal seam scheme.A thermal-hydraulic-mechanical coupling model of coal seam gas displacement by injection of N2-O2mixed gas was established,and COMSOL software was used to analyze the evolution characteristics of coal seam gas pressure distribution,gas pressure evolution law at key intercept points,gas output promotion effect analysis,and coal seam temperature analysis.The distribution evolution characteristics and the dynamic evolution law of the coal seam permeability ratio are simulated,and multiple sets of gas injection pressure,coal seam initial temperature and coal seam initial permeability are set to study the influence of key parameter changes on the above laws.This study has achieved the following main results:（1）The basic parameter tests of coal and gas were carried out,including coal sample solidity coefficient determination,mercury injection experiment and pore volume analysis,gas isothermal adsorption test,coal seam gas content measurement,coal seam gas pressure test and coal seam permeability coefficient monitoring.Research on the hole sealing technology of layer drilling and invent two brand new hole sealing methods:a high expansion and high resistance expansion casing gas drainage sealing method and a hole sealing method for anti-collapse holes in mine drilling gas drainage method,the drilling sealing performance is significantly improved.（2）The thermal-hydraulic-mechanical coupling model of N2-O2 mixed gas displacement gas drainage was established and the reliability of the model was verified using historical data,including matrix gas diffusion control equation,fracture gas and water migration control equation,coal seam The temperature field control equation,coal seam geomechanics response and dynamic permeability change control equation lay the foundation for systematically revealing the process and mechanism of N2-O2 mixed gas displacement gas drainage and further optimizing gas drainage parameters.（3）The process of coal seam displacement by N2-O2 mixed gas injection was simulated,and it was concluded that the closer to the gas injection borehole,the more obvious the superposition effect of the borehole,and the faster the CH4 pressure drop rate,which showed a decreasing trend with time.The closer to the gas injection and extraction boreholes,the more obvious the expansion effect of the matrix and the lower the permeability ratio.Within the influence range of gas injection and drainage drilling,the farther away from the drilling,the higher the permeability ratio,and the later the peak of the permeability ratio appears.（4）Change the key gas injection drainage parameters to analyze the influence on the gas drainage law.The higher the gas injection pressure,the stronger the effect of promoting gas drainage,and the higher the cumulative production and maximum production rate.With the increase of gas injection pressure,the peak value of the permeability ratio at the cutoff point gradually decreases,and the overall change rule remains unchanged.The final average CH4 pressure of the coal seam is inversely proportional to the initial temperature and permeability of the coal seam;the production rate and cumulative production of CH4 are inversely proportional to the initial temperature of the coal seam and directly proportional to the initial coal seam permeability.The thesis contains 44 figures,16 tables and 124 references. |
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