| Dawan Coal Mine is located in Liupanshui City,Guizhou Province.It is a outburst mine under Shuicheng mining area.The main coal seams are characterized by high gas content,high gas pressure and low firmness coefficient,which are typical soft and low permeability outburst coal seams.The effect of coal seam gas drainage is poor,and the expected effect can not be achieved in a short time.With the gradual extension of mining activities to deep areas,the amount of gas emission increases sharply,and the mining connection is tight.Therefore,the corresponding permeability increasing measures should be taken to strengthen coal seam gas drainage.In this paper,based on the research object of gas drainage hole through seam in X103 floor gas drainage roadway of Dawan Coal Mine West well,using the method of theoretical analysis and numerical simulation,the gas migration law of coal seam,the mechanism of hydraulic fracturing permeability,the change of stress field of coal and rock mass before and after fracturing are systematically studied and analyzed,and the field hydraulic fracturing permeability experiment is carried out in X103 floor gas drainage roadway The conclusions are as follows:(1 The measured maximum gas pressure of each main coal seam in Dawan Coal Mine is 3.38mpa,the gas content is 11.5m3/t,the permeability coefficient of coal seam is 0.0167～0.7869m2/(mpa2.d,and the attenuation coefficient of 100m borehole is 0.0032d-1,which is between the coal seams that are difficult to be drained.(2 FLAC3Dsimulation software is used to analyze the stress field of fracturing borehole and roadway deformation before and after hydraulic fracturing.The results show that there is stress concentration on the left and right sides of bottom pumping roadway before hydraulic fracturing,the displacement of floor is 2cm,the maximum displacement of roof is 1cm,and the maximum displacement of two sides of roadway is 3cm.In the process of hydraulic fracturing,the water pressure applied on the fracturing borehole is superimposed with the original rock stress,and the stress gradually decreases along the center of the borehole.The maximum stress is located in the center of the borehole,and the stress is 29mpa.The displacement of the roadway roof and left side increases by 4cm and 2cm respectively.After hydraulic fracturing,a pressure relief zone is formed around the borehole,the stress of coal seam in the pressure relief zone is reduced,the deformation of roadway is small,and it is always in a stable state.（3）After field hydraulic fracturing,the average water content of coal seam increases by 1.8～8.7 times,and the gas content of coal seam decreases by 5.2%～36.4%.Based on the changes of water content and gas content of coal seam,it is concluded that the influence range of hydraulic fracturing drilling is up to 40m along the strike of coal seam and 30m along the dip of coal seam.（4）After hydraulic fracturing,the measured gas pressure of pressure tap 1 is0.71mpa,and that of pressure tap 2 is 0.68mpa.Compared with the original gas pressure of 11 coal seam,it is reduced by 2.63 times,the risk of coal seam outburst is greatly reduced,and the effect of fracturing permeability is remarkable.（5）By comparing the average pumping concentration and the average single hole pumping pure quantity before and after hydraulic fracturing,the average single hole pumping concentration and the average single hole pumping pure quantity after 100days of drilling are observed.The results show that the drainage effect is greatly improved compared with that before fracturing,in which the average gas drainage concentration is increased by 0.96～1.50 times,and the average single hole drainage purity is increased by 1.02～1.77 times.Considering the drilling cost and extraction stability,the best extraction drilling effect is achieved when the construction spacing around the fracturing drilling is 8m.Based on this,the design scheme of coal seam hydraulic fracturing drilling in Dawan Coal Mine is proposed.This paper has total 49 pictures,9 tables,and 88 references. |
