| At present,coal and gas outburst accidents still occur from time to time,especially for Guizhou Province,most coal mines have close coal seams,large gas,and complex geological conditions.The probability of outburst accidents is particularly high.In order to solve this problem,Qinglong Coal Mine first introduced long-distance directional drilling rigs in Guizhou Province,using floor comb-shaped long-distance directional drilling for large-scale gas control.In order to improve the gas drainage rate,optimize the drilling gas drainage parameters,rationally design the drilling holes,and improve the gas drainage efficiency,it is very important to mine the coal mine efficiently.In this paper,research methods such as theoretical analysis,field test,numerical simulation and engineering practice are used to study the law of gas emission from the borehole and the extraction mechanism to optimize the gas extraction parameters of the borehole and the large area gas drainage design.the following research is mainly carried out through the combination of theoretical analysis,field test and engineering practice.(1)Based on the study of the gas development characteristics around the borehole and the mechanical characteristics of the gas around the borehole,the mathematical model of gas emission was obtained by using the radial unstable flow equation and the finite difference method,and the gas emission law was obtained through simulation.With the increase of time,the amount of gas emission first increased sharply.When the rig stopped,the amount of gas emission peaked,and then slowly decreased,and the rate of decrease was getting smaller and smaller.(2)In the Qinglong Coal Mine,a field test was carried out on the gas extraction radius by the pressure drop method,and combined with the gas flow equation of the borehole,the effective extraction radius of the Qinglong Coal Mine was determined to be 3m;and the field test was taken for the first time to reduce the negative pressure attenuation change of the borehole gas extraction Study on the situation,according to the real-time monitoring of the borehole gas negative pressure to obtain the coupling relationship of the suction negative pressure in the 100-meter borehole along the borehole depth direction,that is,the negative pressure decreases by 1KPa per 100 m,providing a theory to ensure that the negative pressure at the bottom of the hole is greater than 13 KPa in accordance with.(3)Using COMSOL simulation software,considering the gas seepage characteristics,taking the 16 coal seam of Qinglong Coal Mine as an example,a gas-solid coupling model of gas flow was constructed.The influence rules of various factors on the gas pressure of the pre-drained coal seam under different conditions such as different extraction time,extraction negative pressure and borehole diameter are analyzed.Taking the Qinglong Coal Mine as the engineering background,the simulation parameters were used to determine the drilling parameters as the borehole diameter was 96 mm and the negative pressure was 25 KPa.(4)According to the above parameters,drilling works are carried out in the 3# drill field in the lower part of the first mining area of Qinglong Coal Mine.After field verification,it is shown that the drilling construction is carried out according to the optimized drilling layout parameters.Compared with ordinary drilling,the gas drainage pure volume is increased by 16 times,and the gas drainage volume fraction is increased by about 50%.The extraction effect of long-distance directional drilling has been significantly improved,which has created safe conditions for the high-yield and high-efficiency of soft and outburst coal seams. |
PDF Full Text Request