Research On The Technology Of Long Boreholes In Roof Instead Of High Drainage Roadway In N2201 Work Face Of Yuwu Coal Mine

With the increase of mining intensity and mechanization,the pressure for preventing and controlling gas in fully mechanized top coal caving face is increasing.Most mines usually use high drainage roadway to effectively control the gas emission from the goaf and adjacent layers.But high drainage roadway also have the disadvantages of high construction cost,long construction period,and tension in mining.In recent years,with the continuous improvement of drilling equipment and drilling technology at home and abroad,coal seam methane technology has been rapidly developed in long boreholes,and trials to replace high drainage roadway with long boreholes in roof have also begun.However,there is a lack of basis for the selection of drilling parameters,and the limitations of the extraction effect cannot be guaranteed.In this paper,the main research object is the engineering background of using the high drainage roadway to control the gas in the N2201 work face of the Yuwu Coal Mine.The paper proposes the use of long boreholes in roof to replace the gas extraction technology of the high drainage roadway and studying the best extraction parameters for long boreholes.By comparing the effect of gas extraction to verify the feasibility of implementing long boreholes in roof instead of high drainage roadway in the N2201 working face.It has guiding significance for the actual production of the mine.Through theoretical analysis and numerical simulation,the main research contents of this paper are as follows:(1)The principle of long boreholes extraction technology was studied,and the drainage amount equation of long boreholes under steady radial flow of steady seepage was constructed.The factors affecting the effect of long borehole gas drainage in roof were analyzed.Combined with the practical experience of mine engineering,the features of"three zones"and“O”shape circle distribution of overlying strata were used to preliminarily determine the drilling layout range of 15~50m height from the bottom of the coal seam floor.The horizontal distance of the lane is 15~65m.(2)The Fluent simulation of the gas migration and extraction effects of goaf before and after high drainage roadway extraction.The gas concentration at the shallow return side of the goaf under the extracted conditions is reduced,and the high concentration gas at the deep return side of the goaf is not significant.Under the action of the negative pressure in the high drainage roadway extraction,the high concentration gas at the shallow return side of the gob area is gathered from the upper corner to the high alley and extracted out of the goaf,and the concentration of gas in the upper corner is up to standard.Therefore,high drainage roadway achieved stable extraction in the crack zone.(3)The Fluent simulation was used to study the effect of long boreholes in different drainage pressures,and the optimum suction negative pressure of the drilling was determined.The analysis results of the drainage effect of long boreholes at the suction negative pressures of 10 kPa,15 kPa,20 kPa,and 25kPa show that with the increase of the negative pressure in the extraction,concentration of gas extraction and gas concentration in the upper corner tend to decrease,while the extraction of scalar and the mixture tend to increase and and increase speed tends to decrease.Considering gas concentration of the upper corner and concentration of extraction under different negative pressures,long boreholes with the negative suction pressure of 20 kPa is best.(4)The Fluent simulation was used to study the effect of long boreholes at different layouts,and the optimal layout of the drilling was determined.The analysis and comparison of the effects of long boreholes in the roof when the drill hole layout is 20m,25m,30m and 35m from the floor of the gob area shows that with the increase of the arrangement height,gas concentration in the upper corner,concentration of gas extraction and extraction of scalar tend to increase,while extraction of the mixture tends to decrease.Considering total volume of pure gas and gas concentration at the upper corners with different deployment heights,long boreholes with the height of the arrangement of 25m is best.(5)Comparing the simulation results of long boreholes and high drainage roadway,it can be seen that the effect of long boreholes on the return side of goaf area is greater than that of high drainage roadway.The scope of influence on the inlet side of the borehole is smaller than high drainage roadway.The quantification results in total drilling total amount of pure gas extraction volume of 11.71m~3/min,which is better than the 11.27m~3/min of the high drainage roadway,the average drilling concentration is 11.96%higher than5.10%of high drainage roadway extraction concentration.The highest extraction concentration of single hole reaches 22.85%.Which verifies that long boreholes achieve the drainage effect of high drainage roadway.(6)According to the cost of construction,the investment in long boreholes reduced by 34.38%compared to the investment in the high drainage roadway.And the construction period is shorter,which relieves the restriction of the speed of high drainage roadway driving on the production of the mining face,and provides a feasible basis for the replacement of the high drainage roadway by long boreholes in roof.Based on the comprehensive consideration of geological conditions,extraction requirements and construction costs,the calculation formulas and applicable conditions for replacing the high drainage roadway with long boreholes in roof were proposed.