Research On Long Borehole Drainage Technology With Large Diameter Roof Strike In High Gas And Thick Coal Seam

Due to the poor gas control in the goaf of the high gas and thick coal seam,and the upper corner gas often exceeds the limit,the roof strike long borehole is used to control the gas in the goaf and control the gas concentration in the upper corner of the working surface.However,when arranging the position and parameters of the long drilling holes in the roof direction,the mine usually only relies on field experience,which results in low drilling efficiency and poor gas control effect in the working face.In view of the above reasons,this paper starts the research on the long drilling technology of the large-diameter roof strike,and determines the optimal roof strike long drilling hole layout and drainage parameters through the research to provide reference value for the management of similar gas over-limit situations.This paper takes the mined-out area of 5309 working face of Sihe Mine as the research object.Based on the evolution law of the overlying strata cracks and the gas migration law in the mined-out area,the main gas accumulation areas in the mined-out area are analyzed.Use FLUENT numerical simulation software to simulate and analyze the timeliness of the drainage effect of long boreholes with different vertical distances,different distances from the return airway,different spacings,and different drainage negative pressures.The results show that:As the vertical distance between the long borehole and the bottom plate increases,the gas drainage scalar of the borehole first increases and then decreases,and the gas concentration in the upper corner increases;as the distance between the long borehole and the return airway increases,the borehole gas drainage scalar first increases and then decreases,and the upper corner gas concentration shows a trend of first slowing down and then increasing;with the increase in the distance between the long boreholes along the roof direction,the borehole gas drainage scalar first increases and then decreases.The gas concentration in the upper corner decreases first and then increases;with the continuous increase of negative pressure in the long borehole along the roof direction,the scalar amount of gas drainage in the borehole has been increasing,and the rate of increase slowed down,and the gas concentration in the upper corner has been decreasing.The rate of decrease slows down,because the negative pressure of the long hole in the roof direction is too large,it will increase the air leakage in the goaf and cause spontaneous combustion.Therefore,through comprehensive analysis,it is determined that the best placement of long holes in the roof direction is 38m from the roof vertical height,25m from the return airway,and 10m between the boreholes.The best drainage parameter is the drainage negative pressure of 20KPa.Applying the above research results to the 5309 working face of Sihe Mine,analyzing the on-site monitoring data and comparing the results of drilling drainage before and after optimization,the average drainage scalar volume of the main pipe reached 7.98m~3/min,and the gas concentration in the upper corner was reduced to 0.21%.The feasibility of the optimal hole layout and drainage parameters was verified,the gas treatment effect was significant,and the safe and normal production of the working face was restored.