Study On Technology Of High Pressure Water Jet Slotting To Intensify Gas Drainage

Gas accident is a major natural disaster which threatens the mine safety,the gas drainage has played a significant role in the mine safety. Although a great quality of research work in the gas drainage of coal mine have been carried out by the specialists at home and abroad, the efficiency of gas drainage was low. Stress release is a crucial means of improving gas drainage rate of coal seams with low permeability, and the research on key technology has exerted a profound influence on the gas disaster prevention of coal mine.This thesis focuses on solving the problem of gas drainage of coal seams with high gas content and low permeability,and proposes the technique of high pressure water jet slotting to intensify gas drainage, which changes the mechanical nature of coal seams in an attempt to improve the permeability of coal seams by means of reducing the original rock stress and increasing permeability of coal seams.Based on the theory of gas flow,and the mechanism of stress release by high-pressure water jet slotting,the effect of stress release after slotting and the slotting parameters have been simulated and analyzed with the help of FLAC5.0, the results indicate that stress release,displacement and fracture occurred about the slot after slotting.Moreover, on the basis of the water jet theory and other relevant factors, the structure of the nozzle has been designed using a commercial program FLUENT, and orthogonal experiment aiming at optimizing the parameters of the nozzle's geometrical structure has been carried out, and the high pressure water jet slotting was created through improving the equipments of the whole system, then the tests of the reliability and stability of the system's performance have been conducted. Finally, combining the above mentioned simulation results with the conditions of the work face, the borehole layout and slotting parameters have been determined. The field work has demonstrated that the technique can effectively release stress of coal seams so that it can improve the permeability of coal seams. Thus, the quantity of gas drainage and the gas concentration have been increased 3.55 times and 37% on the average respectively.