Research On Numerical Simulation About Radius Of Degassing Borehole

Gas drainage is the fundamental measure of the gas accident prevention andcontrol in coal mines, and it has a better function of the gas outburst prevention and thecomprehensive management of gas. The effective radius of degassing borehole is animportant parameter of the measure and it is directly related to the borehole’s design,layout and the length of drainage time. The negative drainage pressure loss from theorifice to the bottom of a borehole and whether it will affect the effective radius ofdegassing borehole and drainage effect or not, there is still no quantitative research now.So the study on the effective radius of degassing borehole and the drainage negativepressure loss are of great significance.Based on the theory of coal seam methane occurrence and coal seam gas flow, thepaper built the mathematical model of the gas flow around the borehole and thenegative drainage pressure loss. And the paper carried out a calculation of the gaspressure distribution around the borehole and the drainage negative pressure loss byusing the finite difference method. It also analyzed the influence of the coal seam gaspressure, coal seam permeability, drainage time, drainage negative pressure and theborehole diameter on the drainage negative pressure loss and the effective radius ofdegassing borehole. So the paper obtained the negative pressure losses and the effectiveradius of degassing borehole at different times under the normal situation and the caseof blocking holes. The results show that the value of the negative pressure loss is verysmall and it has little influence on the effective radius of degassing borehole, and theeffective radius of degassing borehole increases with the extension of the drainage time.Under the condition of the same coal seam occurrences, the effective radius ofdegassing borehole and time become into a power function relationship. And the coalseam gas pressure and the permeability of coal seam play important roles on theeffective radius of degassing borehole, the better the permeability of coal seam, thebigger the effective radius of degassing borehole.