| Coal and gas outburst is one of the most severe disasters in coal mine production.Although strictly comprehensive outburst prevention measures have been adopted,outburst accidents frequently occur near small-scale structures.For example,outbursts occur around both normal and reverse small faults,syncline axis and thickened coal seam.Taking the"8.16"outburst accident in the 13th Pingdingshan Coal Mine as a case,the change of coal thickness and its causes in the accident area was investigated using the method of combining laboratory experiment,numerical simulation and field test.The physical property parameters and their variation rules of small structure thick coal belt were obtained,the gas storage performance and outburst disaster characteristics of small structure thick coal area were studied,and the technical principles and methods of prevention and control of outburst disasters in small structural thick coal area were proposed and field test was implemented.The main conclusions are as follows:(1)Ji15-17-11110 working face of coal seam fluctuate as fold shape,fold the crankshaft to nearly east-west,face in 3 coal thickness larger stripe area,the thick coal belt to parallel to face the fault strike,thick coal district oval block distribution,long axis of the ellipse around 120m length,short axial length about 60m,the long axis is two times of short axis.The cause of coal thickness change is that the roof of a coal seam in the working face is hard and thick,while the floor is relatively weak.In the process of folding,the roof and floor have uncoordinated deformation.Simultaneously,the Sichuan thrust and nappe caused the coal seam to produce wavy undulations parallel to the fault strike,and the wavy undulations were superimposed with the original strip thickening belt high angles.The thicker the coal seam was,the thin one was thin,and finally,the small structural thick coal belt was formed.(2)The small structure thickness with the basic physical parameters of coal and coal adsorption-desorption characteristics difference apparent,is at the core of small structure with thick coal thickness is bigger with thin coal and coal seam position compared to coal,gas radiation initial velocity is big.In terms of adsorption-desorption,the coal gas adsorption capacity is large and the desorption speed is fast at the thickening coal belt of the small structure.In contrast,the gas adsorption capacity is small and the desorption speed is slow at the thinning coal belt.(3)The thick coal belt of a small structure has uneven stress distribution and gas enrichment characteristics.The more significant the change of coal seam thickness,the higher the stress concentration degree,and the more conducive to gas storage.Influenced by initial stress concentration,small tectonic thickening belt ends forming low permeability zone,combined with the roof and floor rocks of the gas block,make small structure thickening with coal not only has the strong ability of gas storage,and gas migration along coal seam or jump rock hard trap conditions,eventually forming thickening with the characteristics of gas enrichment.(4)Under the influence of mining stress in the thick coal belt of a small structure,the sudden decrease of mining stress in front of the working face provided part of the coal body's elastic potential energy for a gas outburst.Meanwhile,mining broke the low permeability zone barrier so that a large amount of gas accumulated in the gas pocket could quickly expand and do work to the working face,thus easily causing gas outbursts.The location of outburst has the characteristics of advancing from thin coal seam to thickened zone.The most effective measure to control gas outbursts in a small structure's thick coal belt is pressure relief.The perforating hydraulic cavitation drilling can not only be used as a geological hole to explore the thickness of coal seam but also play the role of pressure relief,increase and expand penetration.Therefore,the perforating hydraulic cavitation drilling is selected to control gas in the small structure's thick coal seam.(5)In the working face of Ji15-17-11110,the perforating hydraulic cavitation was carried out to control the coal seam gas in a small structure thick coal zone.First,the coal seam thickness was divided into regions,and the discharge rate of coal powder in each area was 19.9,14.6,20.4and 21.7,respectively.The discharge of a large amount of coal powder made the working face entirely relieved the pressure,which was conducive to rapid gas extraction.After 3?4 months of gas extraction,the maximum residual gas pressure in the working face drops to 0.22MPa,and the maximum residual gas content drops to 5.10m3/t.Both the gas pressure and gas content are effectively reduced,proving that the hydraulic cavitation through beds is efficient and reasonable in treating coal seam gas in the zone with small structural coal thickness change.There are 84 figures,21 tables and 83 references in this paper. |
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