Research On Coal Seam Gas Pressure And Initial Gas Emission Characteristics Of Drilling Holes In A Mine In Guizhou

The coal seams geological conditions in Guizhou province are more complex than in other places of China,and gas hazards often occur in coal mines.The determination of coal seam gas pressure is an important part to estimate the outburst risk of coal seam.However,under the limitation of factors like drilling,borehole sealing quality and actual field technical conditions,it is difficult to determine or the determined the gas pressure of coal seam is quite different with the reality,which leads to the misjudgment in coal mine gas prevention and control work.Therefore,taking the coal seam gas pressure as the start point and choose a certain mine in Guizhou province as the research background,this thesis studied the coal seam gas pressure and the characteristics of the initial gas emission from borehole by theoretical analysis,numerical simulation and experimental research,and discussed the possibility and feasibility to obtain the coal seam gas pressure by the characteristics of the initial gas emission from borehole.The main research contents of this thesis are as follows:?1?Considering the depth of the borehole,the stress conditions at different positions of the borehole were analyzed and the plastic zone range around the borehole was discussed by theoretical analysis.The damage range and permeability variation around the borehole were obtained by numerical simulation under different in-situ stress conditions.?2?The source of initial gas emission in the borehole was analyzed,and the seepage differential equation of the borehole wall and the coal dust gas in the borehole was constructed.Based on Darcy's law,the differential equation is calculated by using the theory of coal seam gas emission and the law of coal fines gas diffusion.?3?COMSOL software was used to simulate the characteristics of gas emission from boreholes under different gas pressure,burial depth,moisture content and permeability.The results demonstrate that the gas pressure is closely related to the initial gas emission characteristics of the borehole.The amount of initial gas emission from borehole increases significantly with the original gas pressure gradient,but the increasing trend decreased gradually,all of which is closely related to the attenuation features of coal seam gas pressure.?4?The initial gas emission test of borehole under different adsorption gas and different gas pressure were carried out on a special designed gas emission test platform.The data of the 8 test groups show that the initial gas emission in the borehole increases follow the increasing gas pressure gradients,while the increasing tendency of gas emission decrease gradually.The whole process is quite consistent with the adsorption characteristics and the desorption limit of coal.Through the contrast test,it shows a totally different initial gas emission characteristics under adsorption of CO₂ and N₂in the drilling process.With a higher adsorption capacity,CO₂ maintains a continue emission with the exposure of coal mass in initial 180 seconds.However,under the N₂adsorption condition,the initial emission met a significant decline in the final period,which is caused by a weaker adsorption capacity and the lower adsorption quantity of N₂ in the coal seam.?5?The research results indicate that the initial gas emission in the borehole is positively correlated with the gas pressure in the coal seam,and the initial gas emission in the borehole is one of the important index that can be used to effectively estimate the gas pressure and the actual adsorption conditions of the coal seam.The thesis contains 33 figures,3 tables and 94 references.