Research On Influence Mechanism And Prevention Technology Of Coal Seam Spontaneous Combustion Caused By Borehole Gas Drainage

Coal spontaneous combustion induced by coal seam gas drainage is one of the difficult problems restricting the safe and efficient drainage of coal seam gas.Due to the change of occurrence conditions of deep coal seams,most deep mines take measures such as increasing permeability and pressure relief,increasing extraction negative pressure,reducing borehole spacing and prolonging pre-drainage time to eliminate outburst and improve drainage rate.However,these measures promote the gas leakage of coal around the borehole,which not only affects the gas drainage effect,but also promotes the occurrence of coal spontaneous combustion.In view of the above problems,taking Pingdingshan mining area as the engineering background,based on the borehole instability collapse model and the gas drainage borehole spontaneous combustion Thermo-hydro-chemistry coupling model,this paper analyzes the influence laws of different factors on the gas drainage effect and coal spontaneous combustion,and studies the key technologies to prevent coal seam spontaneous combustion on the premise of ensuring the gas drainage effect.（1）Based on the occurrence environment of coal seams in Pingdingshan mining area,the internal and external factors affecting gas drainage and coal spontaneous combustion are studied and analyzed,and the influencing factors of gas drainage and coal spontaneous combustion are determined.The experimental results show that the greater the stress and the higher the temperature,the smaller the permeability of the coal seam.The functional relationship expression of the permeability of the coal seam with the change of temperature and stress is obtained by fitting,which provides an experimental basis for studying the air leakage mechanism of boreholes and the law of gas seepage in the coal seam.（2）The numerical model of borehole instability and collapse under roadway surrounding rock stress distribution is established,and the creep characteristics of roadway surrounding rock stress peak,the creep instability characteristics of roadway stress distribution on borehole and the creep characteristics of borehole stress peak are analyzed.The results show that the displacement of the roadway stress peak point increases exponentially with time,the displacement of the borehole stress peak point gradually moves away from the borehole wall along the direction of the borehole diameter with the increase of creep time and stress,and the borehole diameter changes the most in the roadway stress concentration area,revealing the formation mechanism of the borehole air leakage channel and time-varying law of hole diameter.It provides a theoretical basis for optimizing the sealing process and sealing parameters.（3）Thermo-hydro-chemistry coupling numerical model of coal spontaneous combustion induced by borehole gas drainage is established,and the effects of different hole sealing parameters,drainage negative pressure,borehole spacing and roadway temperature on the seepage velocity,oxygen volume fraction,coal temperature,pressure relief gas pressure and Wasi drainage volume around the borehole are studied.The functional relations between relevant factors,gas drainage effect and coal temperature are established respectively,and the influence mechanism of coal seam spontaneous combustion induced by borehole gas drainage is revealed.（4）The division method of coal spontaneous combustion area around the borehole is proposed.The intersection of seepage velocity u≤0.004m/s and oxygen concentration 7%≤C（O₂）≤21%is the"Prone to spontaneous combustion area"of the coal seam,which provides a theoretical basis for the optimization of hole sealing technology and the research of coal seam spontaneous combustion prevention technology.（5）The threshold range of CO gas in the gas drainage borehole as the early warning of coal spontaneous combustion is determined,the hole sealing device of"two plugs,one injection and one row of full-hole deep screen pipes"is developed,the hole sealing parameters are optimized,and the hole sealing effect is tested.Tests have been carried out and good results have been achieved in field tests,providing technical support for the safe and efficient extraction of gas from deep coal seams.The dissertation has 142 pictures,15 tables,and 168 references.