Research On Extraction Effect Change Law Along The Drainage Drilling Hole

On the basis of a combination approach of field test and numerical simulation,change rule of negative pressure in drainage hole has been studied in this paper whenpre-draining the gas. Besides, the influences on gas extraction effect have also beenanalyzed, which include the negative pressure in drainage hole varied with drilling holelength and the hole site drift. And the corresponding results have been concluded, whichhas provide a reference for the reasonable design of drilling hole depth whenpre-draining the gas. Furthermore, it has a certain guiding significance on optimizingthe mine extraction system, designing and checking the regional outburst preventionmeasures. By taking drill holes of No.16031return airway in Jiulishan Coal Mine asstudying object, field test, theoretical analysis, numerical simulation and siteverification have been adopted to conduct the study, which have been defined asfollows:Aspect of field test: by using bunch of pipes method, the site test of the negativepressure in bole hole varied with drilling hole length has been conducted, and its changerule has been concluded after analyzing the test dates. The hole site drift in coal seamhas also been test. Use the determination method of gas desorption index by drill cuttingto test coal seam residual gas content of different hole depth from drilling to0.5mwhich extracted after30days to verify the usability of the model of extraction effectchange law along the hole long.Aspect of theoretical analysis: on the basis of gas occurrence and flow theory, thefactors about affecting gas occurrence and flow theory have been analyzed. Andaccording to theory of diffusion-percolation, mass-conservation equation and idealequation of gas state, the gas diffusion-percolation equation has been established, whichhas provided a theoretical support for numerical simulation.Aspect of numerical simulation: by using software of Comsol and under differentof gas permeability coefficient of coal seam, numerical simulation has been establishedto simulate the influence of gas extraction effect which has made by the negativepressure with different drilling hole length, and its change rule has been concludedunder the low or high gas permeability. Moreover, due to the hole site drift in coalseam, those unbalance influences on gas extraction effect have also been analyzed. In this paper, change rule of negative pressure in bole hole has been eventuallystudied when pre-draining the gas. Besides, under the influence of the hole site drift andthe change of gas permeability, change rule of gas extraction effect has also beenconcluded with the difference of hole length. When drilling the gas with same time, theresults have showed that unbalance influences on gas extraction effect is not obvious incoal seam with low gas permeability, while it is obvious in coal seam with high gaspermeability. Furthermore, the hole site drift of drill hole has aggravated its unbalanceinfluences on gas extraction effect.