Research On Linkage Evolution Mechanism And Application Of Pressure-relief Gas Transportation And Storage Area In High-intensity Mining

As the main production area of national coal resources and an important energy strategy in western China,in recent years,with the continuous improvement of the level of mining machinery and equipment and the degree of intensification of production,the number of highintensity mining longwall face characterized by large mining width and high advance speed has increased.Under the condition of high-intensity mining of coal seams,the gushing intensity and gushing volume of pressure-relief gas increase,and it is difficult to identify the pressure-relief gas transportation and storage area of overlying rock in the goaf,and its morphological characteristics are more complex.As a result,the decompression gas extraction efficiency cannot fully meet the needs of safe and efficient extraction.The article expounds the laws and mechanisms of the evolution of mining overburden fracture,pressure-relief gas migration in goaf and its extraction under high-intensity mining conditions,which can provide a certain theoretical basis for pressure relief gas extraction in high-intensity mining face.Based on the engineering background of typical high-strength mining wells,this paper analyzes the distribution and variation of mining stress,the distribution of overburden fissures,the displacement of rock strata and the characteristics of collapsed rock mass through physical similarity simulation experiments.Based on the fractal theory,the fractal-permeability equation of the mining fracture network is deduced.The permeability variation law of overlying rock was inverted by combining on-site borehole observation and extraction parameters,and the average error between the theoretical model calculated value and the in-field permeability inversion value was 8.11%.The governing equation for calculating the gas flow state based on the opening of the fissure is constructed,and the quantitative criterion for the pressure-relief gas transportation and storage area is put forward.The fracture network is divided into the predominant area for gas migration in fractured fractures,the micro-permeability area in fractured fracture compaction,the predominant area for gas migration in abscission fractures,the gas micro-permeability area in interlayer fracture compaction,and the gas enrichment area in fractured fractures.Through FLAC3D numerical simulation,the distribution characteristics of overlying rock stress,rock stratum displacement and plastic zone under the conditions of different advancing speed and face width are analyzed,and the interaction law of the two factors on the morphological characteristics of the pressure relief gas transportation and storage area is obtained by using the response surface analysis method.In terms of the displacement and stress of the overlying rock,when the advancing speed is accelerated,the stress concentration in the compaction area is significantly reduced,and the scope of the leading area is increased.When the face width increases,the support pressure around the goaf increases,the rock stratum displacement increases exponentially,and the distance to full mining is smaller.The "masonry beam" structure with good rock integrity at the sub-key stratum and the area below are the key areas for decompression gas drainage.When the pushing speed increases,the extension length of the pressure relief gas transportation and storage area increases exponentially,and the inclination width basically remains unchanged.When the face width increases,its strike extension distance decreases,and its inclination width increases.The structural area of the pressure-relief gas transportation and storage area determines the size of the pressure-relief gas storage space in this area,and a relatively suitable gas extraction method can be selected according to the size of the area.the significant influence on the area is:linear effect of thrust,linear effect of surface width,nonlinear effect of thrust,interaction between the two,and nonlinear effect of surface width.The stress recovery and crushing characteristics of broken rock mass in goaf are clarified.Using the crushed rock mass compaction-seepage test system,the compaction deformation,energy dissipation and seepage characteristics of crushed rock mass under different gradations and loading rates were studied.It is found that the compaction process of broken rock mass can be divided into three stages:initial compaction,elastic compaction and plastic compaction.Either an increase in the loading rate or a decrease in the gradation results in a decrease in the length of the first two stages.In the first stage,the intensity and quantity of acoustic emission signals are both relatively small.In the second stage,the number of acoustic emission signals and the cumulative energy dissipation show a linear growth mode,and the third stage shows a decaying growth mode.Increasing the loading rate will lead to an increase in the accumulative count of acoustic emissions and an increase in the event energy level,while an increase in the gradation results in a decrease in the number of events and an increase in the energy level.Under the test conditions,the permeability of the broken rock mass is 1.6×10-9～3.5×10-7m2,and the increase of gradation and loading rate will lead to the increase of permeability tend to zero.The energy dissipation-fractal equation in the process of lateral restraint compression of broken rock mass is established,and the energy dissipation and void change paths of broken particles are obtained.Using the basic principles of elasticity and seepage mechanics,the evolution characteristics of cracks in the process of "O-X" type fracture of the roof are expounded.It is found that the fracture type of low-level strata is vertical "O-X" type fracture,and the high-level rock layer is horizontal "O-X" type fracture,and the critical conditions for the occurrence of two types of fractures are given.It is clear that the pressure relief gas lift channel is the intersection of the "O"type fracture and the "X" type fracture,and its storage space is the interlayer fracture.The migration mode of pressure-relieving gas in low-level strata is mainly seepage and floating,while in high-level strata,diffusion is the main mode.Revealing the linkage evolution mechanism of stress-fracture-gas migration in the pressure relief gas transport and storage area under the condition of continuous advancement of the working face.The influence of working face width and advancing speed on its evolution is analyzed,and the arrangement principle of pressure relief gas drainage system is clarified according to it.Taking the 211 longwall face of Shaanxi Huangling No.2 Coal Mine Co.,Ltd.as the engineering background,applying the above theoretical analysis and test results,combined with FLUENT numerical simulation,it is concluded that the optimal extraction position of this working face is 23 m above the coal seam roof,a distance from the returning airway 25 m.According to the morphological characteristics of the gas transportation and storage area of the working face,the conventional high-level drilling,directional long drilling and the goaf buried pipe layout parameters in the high-speed and low-speed propulsion areas are designed respectively.Through on-site observation,it is clarified that the whole life cycle of drilling and extraction can be divided into long-distance extraction stage,effective extraction stage and shortrange extraction stage.concentrations were decreased.In the actual production process,the pressure relief gas extraction rate has been maintained at more than 80%for a long time,and the gas in the working face,return air lane and upper corner has not exceeded the limit.From the perspective of gas control,the safe and efficient production of the working face is guaranteed.It provides a certain theoretical basis and technical support for the pressure relief gas extraction of this kind of working face.