Study On Influencing Factors Of Effective Radius Of Extraction Based On Seepage Law Of Gas-bearing Coal Body

At present,the use of gas extraction boreholes for pre-drainage of coal seam gas is one of the important means of prevention and control of coal mine gas disasters.With the continuous extension of coal mining in China,the problem of deep high temperature has become increasingly prominent.Due to the influence of coal seam temperature,ground stress and other factors,the migration of gas in coal seam is more complicated,which puts forward higher requirements for gas extraction technology in coal mines.In order to further improve the extraction efficiency of gas in coal seam,this paper explores the seepage law of gas-bearing coal and the influence of different factors on the effective radius of extraction,and explores the influence of confining pressure and temperature on coal permeability by means of multi-phase and multi-field dynamic seepage experimental system of coal rock.Based on the existing research,the control equations of coal deformation,gas migration and temperature field are derived.According to the actual situation of 131306 glue transport crossheading in Liuzhuang Coal Mine,the equation is embedded in COMSOL Multiphysics software to construct a three-dimensional bedding gas extraction borehole model for solution.The effects of gas extraction time,coal seam temperature,coal seam permeability,negative pressure of borehole extraction,borehole diameter and borehole spacing on the extraction radius of gas extraction borehole are studied.Thus,the influence law of different factors on the extraction radius of gas extraction borehole is obtained.The main research contents and results are as follows:1.Gas-solid coupling experiment and force-heat coupling experiment were carried out by means of multi-phase and multi-field dynamic seepage experiment system of coal rock.By changing the confining pressure and temperature of coal body,the influence of confining pressure and temperature on coal rock permeability was obtained.Based on the opening and closing degree of pores and fissures in coal body and the change of seepage space,the influence of confining pressure on coal permeability is studied.It is found that with the continuous loading of confining pressure,the compression degree of coal body is increasing,and the pores and fissures in coal body are gradually compacted,which leads to the decrease of coal permeability.With the decreasing space of pores and fissures that can be compressed inside,the decreasing trend of coal permeability will gradually slow down and slowly tend to be gentle.The influence of temperature on coal permeability is analyzed from the perspective of thermal stress.When the temperature rises,the thermal stress generated inside the coal body will lead to the expansion of the coal skeleton and particles.Due to the binding effect of the external axial pressure and confining pressure of the coal body,the thermal expansion can only act on the inside of the coal body,so that the internal pore and fracture space of the coal body becomes smaller,the gas seepage channel becomes narrower,and the permeability decreases.Therefore,the permeability of coal decreases with the increase of coal temperature under the condition of 20°C-65°C.2.On the basis of previous studies,the control equations of coal deformation,gas migration and temperature field are derived and embedded in COMSOL Multiphysics software.Taking the glue transport crossheading of 131306 working face in Donger 13^-1coal seam of Liuzhuang Coal Mine as the research object,a three-dimensional bedding gas extraction drilling model is established.By solving the model,the influence of extraction time,coal seam temperature,coal seam permeability,borehole spacing,borehole diameter and negative pressure on the effective radius of extraction is studied.According to the results of the simulation,some suggestions are put forward for the design of the bedding borehole in the 131306 glue transport trough of Liuzhuang Coal Mine.When the coal seam temperature is in the range of 20°C to65°C,the permeability of the coal seam decreases with the increase of the coal seam temperature,and the low temperature is more conducive to the extraction of coal seam gas.When the coal seam permeability increases from 0.70×10^-16m²to 1.50×10^-16m²,the gas extraction time can be shortened by 84 days.After 180 days of extraction,there are still areas where the extraction is not up to standard in the boreholes with a spacing of 8m,and the spacing of the holes can be set to 6m.The drilling hole of 94 mm diameter is used in 131306 glue transport crossheading.If the drilling hole of 143 mm diameter is selected,the effective radius of extraction will be increased by about 13%.After 180 days of extraction,the effective radius of gas extraction under 30 KPa negative pressure is 3.037 m,and the effective radius of gas extraction under 10 KPa negative pressure is 3.003 m,so there is no need to increase the negative pressure of drilling.Figure[39]Table[8]reference[105]...