| In Chinese energy industry,coal still occupies a large proportion.In the process of coal mine production,goaf gas control has been the focus of work.Due to the movement of overlying strata and complex fracture development caused by coal seam mining,gas migration and accumulation in fracture zone is the key research content of gas drainage in goaf.In this paper,the 50105 working face of the first mining layer in Faer Coal Mine is taken as the engineering practice,and the research is carried out through theoretical analysis,numerical simulation and engineering experiment.The main research contents and results are as follows :By constructing a two-dimensional discrete element numerical simulation model and simulating the state of overlying strata in the engineering field,the development height of the caving zone is 14.5 m and the development height of the fracture zone is50 m.By simulating different mining distance of coal seam,the movement characteristics of overlying strata and the distribution law of fracture development after coal mining are obtained.The overlying strata in the study area are less stratified and the height from coal is low,so the control effect of strata is weak,and the failure of overlying strata is obvious in the process of short-distance mining.With the continuous advance of mining,the overlying strata in the goaf tend to be stable,and the rock movement characteristics change little,and the subsidence of each rock is relatively close.Based on the calculation results of the empirical formula and the numerical simulation results,the overburden rock detection in the engineering site is carried out.Through the mutual verification of the network parallel electrical method and the borehole camera method,it is obtained that the development height range of the overlying strata caving zone is 13.5 m ? 15.0 m,and the development height range of the fracture zone is 51.7 m ? 53.6 m.Through the combination of numerical simulation and engineering field experiment,the comprehensive analysis shows that after the overlying strata stabilize,the fracture development concentrated area is mainly distributed on both sides of the overburden failure zone.There are a small amount of fractures in the overlying strata in the unmining areas on both sides,and the fracture recompaction occurs in the middle of the goaf.According to the development of fractures,it is determined that the area with horizontal width of 0 m ? 40 m on both sides of the overburden failure zone is the dominant channel range of gas migration below the longitudinal height of 40 m.Based on the fluid mechanics motion equation,the gas flow model in the fracture zone is constructed.According to the fracture distribution of overlying strata,combined with the finite element numerical simulation software,the gas migration and accumulation process in the fracture zone is studied.Through the analysis,it is obtained that the gas mainly migrates upward through the dominant channel in the fracture zone until it stops at the top of the fracture zone,and slowly diffuses between the micro fractures in other regions.The gas concentration in the fracture-intensive area is the highest,and after the concentration reaches a certain value,the gas mainly accumulates in the dominant channel and the top of the fracture zone.Based on the above research,combined with the relevant geological conditions of the study area,the advantages of gas drainage area are analyzed,and the reliability of the research results is verified by combining with the high and long distance directional drilling gas drainage technology. |
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