| Gas pre-extraction is the key technical means to solve the problem of gas,and the extraction radius is the basis of gas extraction.The accurate determination of extraction parameters is of great significance to the safety production of coal mines.In this paper,the permeability of coal seam is low and gas extraction is difficult.In order to achieve the purpose of efficient extraction,scientific and effective drainage hole layout design is essential.Therefore,it is of great significance to determine the effective gas extraction radius accurately for the layout of pre-extraction borehole and the safe mining of coal seam.This paper takes the 5th coal seam of a mine in Lianghuai area as the test area.This coal seam is mainly mined at the 120502 working face.Based on the theoretical analysis of the gas migration mechanism,a gas diffusion-seepage coupling model is established,and the gas pressure is simulated by FLUENT.The changes in the extraction time and the field gas content method to test the effective extraction radius can draw the following conclusions:(1)By numerical simulation of the variation of gas pressure with the extraction time,it can be found that the gas pressure drops rapidly at the early stage of extraction from 10 to 30 days.When the extraction lasted for 60?90 days,the gas pressure drop rate gradually attenuated.After 90 days of extraction,the gas pressure drops to a flat level.The effective extraction radius measured at 20KPa negative pressure and 94mm borehole was as follows:the effective extraction radius of 30d was 2.14m.The effective extraction radius of 60d is 3.43m.The effective pumping radius for 90 days is 5.12m.The relationship between effective extraction radius and time was obtained by data fitting:R=2.01051ln(t)-4.40149.It can be seen that the effective gas extraction radius has an extreme value,and the extraction economy in the later stage is not high(2)The field test adopts the gas content method.The field test uses 20?24KPa negative pressure drainage for two months and three months after the gas content value and the original gas content value.The comparison shows that the effective drainage radius in two months is 3m.,The three-month drainage radius is 5m.The results of the same numerical simulation are in good agreement,verifying the accuracy of the field test results.Through the gas flow method to measure the discharge radius,it is found that the discharge radius of the 94mm borehole is 0.6m.(3)The effective drainage radius value obtained according to the field test and numerical simulation results.According to the construction schedule on the mine,a three-month effective extraction radius of 5m is used as the basis for drilling holes in the 120502 working face.According to the actual working conditions of the 120502 working face,the drafting hole layout plan is formulated:the hole spacing L=9.0m,and the hole diameter is ?D94mm.Figure[59]table[12]reference[94]... |
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