| Pre-drainage of coal seam gas by gas extraction is an effective measure to control gas.It has become the main means to prevent gas outburst and reduce gas emission.Reasonable sealing parameters and excellent sealing materials can effectively improve gas extraction efficiency.Through the research methods of theoretical analysis,numerical simulation,field measurement and industrial experiments,the selection of reasonable sealing parameters and the performance of sealing materials for extraction boreholes are systematically studied.The main results are as follows:(1)By establishing the relationship between roughness and geological strength in Hoek-Brown criterion,the theoretical analysis of surrounding rock stability around boreholes can be optimized.Based on the above analysis,the point safety factor is introduced into the stability analysis of roadway surrounding rock,and the point safety factor based on non-linear Hooke-Brown strength criterion is derived.(2)The stress redistribution of surrounding rock after coal roadway excavation is calculated by FLAC3D5.0 software,and the stress distribution law of surrounding rock under different factors is analyzed.It is suggested that the fissures in the surrounding rock of boreholes should be divided into "fissures and free surface penetration zone" and "non-penetration zone between fissures and free surface".It is suggested that the quantitative criteria of whether the fissures in the surrounding rock of boreholes are "leaking" or whether the fissures in the surrounding rock of boreholes are penetrated with free surface can be characterized by permeability.Qualitative detection of sulfur hexafluoride gas by tracer gas is carried out to verify the existence of "fissures and nonpenetration"(3)The quality of crack plugging is mainly related to a series of related factors,such as the nature of sealing materials and the scale of cracks,but it can not be explained that the crack plugging simulation can not be carried out because of the high degree of crack development in the loosening zone.Based on Comsol's dual porous medium gas migration model combined with coal and gas-solid coupling,it is determined that the reasonable sealing depth is within the pressure relief zone but beyond the "nonpenetrating zone between cracks and free surface".On the basis of reliable sealing materials,different sealing length has little effect on gas drainage effect,but longer sealing length will lead to the reduction of effective drainage length,which will lead to further production.There is a high gas pressure gradient near the sealing hole section,which is not conducive to the improvement of gas extraction effect.(4)By systematically studying the macro-mechanical properties of SNZQ material,the whole reaction process of hydration system and the micro-qualitative and semiquantitative analysis of hydration products,the hydration mechanism of borehole sealing material was studied through four experimental variables: water-cement ratio,type of gypsum,content of gypsum and fineness of aluminium powder.(5)Through the field test of 11111 coal face in Wanghangzhuang Coal Mine of Guotou Henan Xinneng Development Co.,Ltd.,the rationality of the selection of sealing parameters and the excellent sealing performance of SNZQ sealing material are verified. |
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