| In order to improve the recovery rate of coal resources and ensure the safe production of the recovery process,this thesis analyzes the preferential selection of the first mining protection layer and determines the 15 coal as the first mining layer.The main research object,using theoretical analysis,numerical simulation and field verification methods to study the overlying coal(rock)seam collapse characteristics,fracture development and gas transport law,study the feasibility of upstream mining after the first mining 15 coal and the overlying coal seam gas extraction technology program,and in the field construction to verify the gas extraction effect.The following conclusions were mainly obtained:1)The study on the preferred analysis of the first mining protection layer of the mine was carried out.The maximum gas content of 13 coal is 14.80m~3/t;14 coal is14.71m~3/t;15 coal is 6.88m~3/t.The numerical simulation of UDEC software was used to obtain the unloading law and expansion deformation characteristics of the coal seams adjacent to different coal seams,and combined with the degree of coal seam protrusion risk,coal seam Combining with the risk of coal seam protrusion,the effect of coal seam pre-discharge and coal seam storage conditions,the study determined that the 15 coal was mined as the first protected seam.2)Taking 21502 working face as the research object,the deformation,displacement,stress change and fissure development law of the overlying coal rock body during the 15 coal recovery process were studied.The recoverability of 13 and 14coal after mining of 15 coal was studied and analyzed using various upward mining discrimination methods,and the results showed that 13 coal is located in the middle and upper part of 15 coal fissure zone,and 14 coal is in the transition area of collapse and fissure zone.Using UDEC software simulation to get mining 15 coal overlying coal rock subsidence law;stress concentration phenomenon is obvious at the position of cutting eye and stopping line;the fissures in the middle area of mining area during 15coal back mining are developed first and then closed,and the fissures in the working face range show a ring-like development.Combining the theoretical and simulation results,the range of 15 coal collapse zone is from 0 to 9.02 m,13 and 14 coal are located above the collapse zone,and the mining interval of 13 and 15 coal should be more than6 months.3)The fracture development and damage characteristics of the overlying coal seam after 15 coal mining were observed and analyzed in the field by using borehole imaging and downhole water injection observation methods.From the borehole imaging,the larger fractures in borehole#1 are mainly distributed from 7.5 m to 9.5 m;in borehole#2,the larger fractures are mainly distributed from 6.5 m to 8.8 m;in borehole#3,the larger fractures are mainly distributed from 7.2 m to 9.3 m.From the downhole water injection observation,the average water injection amounts in the front section of the two observation boreholes are 4.525 L/min and 4.143 L/min,respectively;The average amount of water injection in the middle section is 9.858 L/min and 8.893 L/min;the average amount of water injection in the back section is 8.169 L/min and 7.375 L/min.The development height of the 15 coal collapse zone is 9.01 m.The 13 and 14 coals appear to settle after the 15 coal mining,except for the local areas related to the cuttings,the stop line and the four corners of the mining area,which may produce the step phenomenon.All the other areas can be normally recovered after the 15 coal mining is stabilized.4)Based on the numerical simulation of the three-dimensional distribution model of porosity,the gas transportation law of the overlying coal(rock)seam of 15 coal was studied.Based on the fracture development of the overburden rock of 15 coal,we analyzed the dominant channel of gas transportation,constructed and calculated the segmental 3D distribution formula of porosity of the overburden rock on the working face,and used FLUENT software to analyze and study the gas transportation law of the overburden rock on the working face of 21502.The results showed that in order to avoid the gas overrun problem during the recovery period,we should use both the upper corner buried pipe and high drilling to extract gas.5)Based on the fracture development law of the overlying coal rock body after 15coal mining and the gas transportation advantage area,combined with the simulation results of FLUENT software,the gas extraction measures during the back mining of21502 working face were optimized,and the field extraction results showed that the gas extraction volume was effectively improved,and the gas concentration in the upper corner and return airway was reduced,and the gas extraction effect was verified by the residual gas content of the overlying coal seam.The optimally designed gas control measures ensure the safe recovery of the working face and eliminate the gas threat of the overlying coal seam.There are 65 figures,28 tables,and 95 references in this thesis. |
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