| The geological factors including high gas pressure,low permeability,and soft coal have always been the primary concern and difficulties that results in the ineffectiveness of gas control for coal mines in China and the frequent occurrence of gas related hazards,especially in Guizhou province.Hydraulic punching is widely used for pressure relief in coal mines,but hydraulic measures are very questionable in Guizhou province,because the lack of in-depth analysis of the coupling evolution of hydraulic punching,pressure relief.So,in this thesis,the Songhe coal mine in Panjiang,Guizhou Province with soft,low permeability,distance and high outburst index coal seam is chosen as the subject.The physical and mechanical properties of the coal are experimentally tested and analyzed,and the coupled model of coal fracture deformation,pressure relief,and gas migration is established.We study the multiphysics coupling effect of hydraulic punching of coal and its synergistic mechanism of pressure relief and gas drainage,then,we test the hydraulic punching measures in Songhe coal mine and evaluate the effect of pressure relief with gas drainage.The main research results are as follows:(1)We analyze the pour,micro fracture and gas adsorption characteristics of coal samples in the laboratory.Considering the porosity and permeability independently,a dynamic evolution mo del including strain and gas pressure is purposed,where the interaction between coal deformatio n and gas pressure are established according to the Klinkenberg effect and the Kozeny-Carman e quation.Our dynamic evolution model of permeability is a gas-solid coupling model.The matchi ng between the model's prediction and in-site data,and the comparison between our model and t he results from previous models prove that our model can be applied to simulate the gas-solid co upling phenomenon of the coal seam with low gas permeability..(2)We conduct numerical simulation of the multiphysics coupling between hydraulic punching and pressure relief drainage with a single hole,double holes and multi-holes under different pore diameters and pore spacings.The simulation shows that after coal seam hydraulic punching,from the hole to the deep part of the coal body,the stress relieving area,stress concentration area and original stress area are presented;the volume of flushed coal maintains at a constant rate and gas pressure falling to the corresponding indexes.With the increase of extraction time,the effective extraction radius gradually increases.With the increase of punching hole diameter,the larger the stress migration range of the coal body,the larger the displacement of coal around the hole and the faster the gas pressure drops.The effective radius of influence is greater;for double holes and multi-holes punching,the stacking effect is significant,the smaller the hole spacing or the larger the hole diameter,the better the pressure relief effect between the holes in the coal body,resulting in larger displacement and greater pressure drop.(3)The electromagnetic radiation(EMR)signal generated by hydraulic punching and coal breaking is monitored on site,and the analysis reveals that the EMR response law of hydraulic punching conformed to the Hearst statistical law.During the punching process,the EMR signal increases with the increase of the punching time.The stronger the EMR signal is,the fiercer the coal body ruptures and deforms,and the signal that is abnormally strong at the time of the punching fully confirms this.After the punching process,the EMR signal is greatly reduced but still higher than the signal before punching,indicating the coal body's rupture during the punching process,and the mechanical behavior is relatively quiet,but the fracture or deformation within the coal body is still slowly proceeding.(4)The on-site monitoring of decompression gas drainage work shows that the gas concentration,flow rate,and stress are reduced with the increase of the hole spacing,and the stress monitoring verifies the results from numerical simulations and industrial tests.That is,with a single hole diameter of 0.8 m,there will be 8 tons of discharged coal,and after a drainage time of about 80 days,the gas pressure drops below 0.74 MPa,and the corresponding effective pressure relief radius is 4.5 m.(5)A high-efficiency evaluation method for hydraulic punching,pressure-relief and gas drainage is proposed.According to the results of numerical simulation and industrial test,and based on the conservation law of mass,we established a model to evaluate the drainage effectiveness,in which the influential radius of the gas drainage and pressure relief area with the constant total volume of the gas are considered.(6)The industrial test results show that the gas drainage effect of hydraulic punching is obviously better than that of the ordinary drilling process.After drilling,the gas content rapidly increases with time,stabilizes at a higher concentration,and then slowly decreases after maintaining for a relatively long time.The original gas concentration in the drilling hole can reach 71%and with the maximum concentration of 85%.The value was maintained for 35 days,which were 1.5 times,1.7 times and 8.75 times that of ordinary boreholes.In the 71 days of industrial test recording,the average daily gas extraction volume is 23.3 m~3 and the total is 1 656m~3,which is 3.19 times more than the ordinary drilling extraction process.The results of this study have important theoretical and practical significance for understanding the multiphysics coupling of coal mining with hydraulic punching in high-burst-potential mine area,the synergy mechanism of pressure-reducing and gas extraction,as well as improving on-site hydraulic measures,which can highly promote the safety and effectively prevent gas disasters in coal mines. |
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