Study On Gas Region Extinction Technique Of Long Distance Directional Drilling In Protruding Coal Seam

Guizhou coal seam geological structure is complex,coal seam gas pressure is large,gas content is high,is not conducive to gas pre-pumping regional extinction.The traditional gas region extinction measures have high management cost,long extraction period and low gas utilization efficiency,which is not conducive to the balance of"pumping,digging and mining"in coal mine.Aiming at the problems of gas control in Guizhou coal mine,this paper studies the technology of long-distance directional drilling gas region of protruding coal seam in qinglong coal mine by theoretical analysis,numerical simulation and field test,and obtains the following research results:Based on Darcy's law,gas content equation,porosity variation equation,Permeability equation and continuity equation,the control equation of gas seepage field in coal seam is deduced,and the stress-strain constitutive equation of force deformation of coal body is introduced according to the unit coal general strain equation,equilibrium differential equation and generalized hook law,and the control equation of gas seepage field in coal seam,stress-strain constitutive equation of force deformation of coal body,The variation equation of coal body permeability is combined with the variation equation of gas permeability,and a fluid-solid two-field coupling model for coal seam gas extraction seepage is obtained.Using COMSOL simulation software,the two-field coupling model of coal seam pumping gas is constructed,and the influence law of gas pressure under different drilling diameter,different extraction negative pressure and different pumping time is studied,and the effective extraction radius of drilling with a diameter of 96mm is greater than that of 65mm and 75mm in diameter.The optimal diameter of 96mm drilling is optimized when the directional drilling is arranged,and the negative pressure of different extraction has little effect on the gas pressure,but increasing the negative pressure of drilling and pumping can effectively improve the gas quantity of drilling,so the negative pressure of 25kPa is optimized when the directional drilling is pumped,and the gas pressure decreases with the increase of the number of days of extraction.However,the decreasing rate of gas pressure shows a decreasing law.According to the optimized drilling arrangement parameters obtained by COMSOL simulation,the bottom plate comb directional drilling construction is carried out in the northern section of Qinglong Coal 21606 mine,and the construction results are as:the actual main hole of each directional drilling is deeply 540m to 600m,the number of branch holes entering the coal seam on each main hole is 5 to 7,the pore rate is high,According to the optimal drilling and negative pressure obtained by COMSOL simulation,the gas concentration and gas purity are obviously reduced,and it is indicated that the gas extraction in coal seam is effectively reduced by the arrangement of long distance directional drilling.By counting the total amount of gas extracted from the directional drilling field in the north section of 21606,the residual gas content of16 coal seam in the control area of the drilling field is calculated as 5.2788m~3/t,the extraction rate is 62.7%,and the residual gas pressure in the area is determined by the field detection point between 0.401-0.615MPa,which achieves the In the anti-protrusion regulation,the residual gas content is less than 8m~3/t,the extraction rate is greater than 30%,and the residual gas pressure is less than 0.74MPa,and the regional extinction effect test requirements.