Research On Time Effectiveness Of Drilling Influence Radius By Injecting Nitrogen To Displace Methane In Coal Seam

Displacing methane by nitrogen injection is one of new techniques for gasextraction and the new concept for gas control. The time characteristic of influenceradius for gas injection is one of key parameters for displacing methane by gas injection.Field tests in Shigang coal mine were conducted for influence radius of gas injection,and then the gas flow of drilling in gas injection process was tested besides the headingface to conform the influence radius of displacing methane by gas injection throughdrillings. The results of field test indicated that though the influence radius of gasinjection increased with the increase of injection time, but the increase was notunlimited. It was also founded that there existed differences of influencing radius of gasinjection between the horizontal and vertical direction.Based on gas seepage law, gas diffusion law, multicomponent gas competitivenessadsorption law, conservation of energy law and the ideal-gas equation, displacingmethane by gas injection was established, and the simulation experiments for influenceradium under different gas injection pressures and times were also conducted byComsol Multiphysics software. Comparing with results of field tests, the simulationresults corresponded very well. On the basis of simulation results, the timecharacteristic of influence radius in gas injection was studied. It can also be concludedthat the difference between the vertical and horizontal direction of the influence radiusof gas injection can be described as power exponential, namely△R=0.1195t^0.272.Through analyzing numerical simulation results, the quantitative relationshipbetween the influence radius of gas injection and gas injection time-t and the gasinjection pressure-p, is R=（0.5072p0.5237） t^{（0.0163p+0.4361）}（0.3≤p≤2MPa）under certaincoal seam permeability and drilling diameter. Through analyzing these, the reasonableinterval between gas injection drilling and emission drilling can be concluded:1.6m inthe horizontal direction and1.4m in the vertical direction between two adjacentdrillings.