Identification And Application Of Overburden Pressure Relief Gas Accumulation Area In Thick Coal Seam Of Yuhua Coal Mine

With the advancement of science and technology,coal mines are basically automated and high intensive mining of thick coal seams with high gas content is the norm.High intensity mining leads to full decompression of this coal seam,resulting in a large amount of gas desorption into free gas,which floats to the production working face,the extraction area and the corner position,causing gas enrichment in some areas and concentration concentration exceeding the limit,posing a serious threat to the lives of coal miners at the production working face.Therefore,by studying and analysing the evolution characteristics of overburden fissures and the mechanism of unloading gas transport after mining and proposing corresponding management measures,we can provide positive safety guarantee for coal mine safety production and have high economic and social benefits,so as to achieve safe,green and scientific co-mining of coal and associated resources.In order to scientifically and thoroughly study and analyse the development pattern of fissures in mining overburden of thick coal seams,the boundary range of fissure field and the enrichment characteristics of highly concentrated unburdened gas in the fissure field of mining overburden,this paper takes 2407 working face of Yuhua coal mine as the test object and identifies the enrichment area of strong mining overburden unburdened gas in thick coal seams by using high-precision micro-vibration monitoring technology and multi-functional intelligent borehole detection equipment in the field,and tests its effect.The main research and results of this paper are as follows:(1)According to the theoretical analysis,the three-dimensional spatial model of the mining fissure field of thick coal seam was initially determined,the sources of gas in the mining fissure area were analysed,the transport pattern of unloading gas in the mining fissure field of thick coal seam was determined,and the enrichment characteristics of unloading gas in the fissure field were clearly defined as:diffusion flow of unloading gas,longitudinal diffusion and floating of unloading gas and horizontal gas enrichment.(2)A fissure field in the overburden of the thick coal seam was established.The fissure field development width,strike length and development height were determined.The theoretical model for the strike zoning of the quarry was optimised.In the vertical direction,microseismic characterisation of the overburden fissure zone was used to characterise the height of 85-105 m.The mechanism of fissure cycle evolution in the overburden of mining and the spatial dynamic evolution characteristics of microseismic events were studied to verify the fissure cycle breakage law of the overburden on the return side of the test face,and to determine the height range of the bubble fall zone from 19.7 to 24 m.(3)The gas enrichment rules in the mining fissure field of thick coal seams are optimised and expanded,and the gas enrichment zones in the mining fissure field of thick coal seams are divided into:gas diffusion and flow zone,vertical gas rise and float zone and high concentration gas enrichment zone.The principles for the identification of boreholes in the unloading gas enrichment zone are determined,and a borehole detection scheme is constructed.Along the direction,the unloading gas on the return wind side is diffused-floated-enriched into the fissure field,with a lag,and with the influence of mining in the first cycle of incoming pressure step during the detection period,the diffusion and floating is basically in the gas flow diffusion zone,and in the second cycle of incoming pressure step,the unloading gas is transported and enriched,and the gas concentration increases more obviously.(4)Based on the identified highly concentrated gas-rich areas,we guided the practice of gas extraction engineering in large diameter boreholes at high level towards the site.The working face and return wind gas management effect was excellent,with concentrations below 0.5%,ensuring safe and efficient coal and gas extraction from the working face.The results of the study provide effective theoretical support for the determination of the final hole of the highly concentrated gas extraction borehole and can effectively solve the problem of serious gas outflow.It is of great relevance to the safety of underground staff,the control of gas concentration in the corner of the working face,the suppression of gas gushing from the extraction area and the saving of gas extraction costs.