Study On Fracture Evolution Of Ultra Thick Seam And Surface Borehole Production Rules Regularity

For high mining intensity and disturbance of ultra thick coal seam, this paper isto determine suitable location of gas extraction and analyse surface boreholeproduction rules.The ultra thick coal seam fractured field evolution law and gasdistribution law have also studied in this paper.The production rules at differentrelationship between permeability and drainage radius have been determined.Thecomparison was made between measured data collected from Weijiadi coal mine inGanSu JingYuan and the theoretical value.Expansion rates and penetration of ultra thick coal seam were studied usingABAQUS software for overlying strata displacement:(1) Roof caving is not sufficient,when the seam is not fully mining. Permeability in central part of gob is larger. Roofcaving is sufficient and rocks overlying collapse fully, when the seam is fully mining.Permeability in central part of gob becomes smaller;(2) Expansion rate andpermeability value closely to ventilation roadway are larger than to intake airway byvirtue of asymmetrical distribution of gravity made by coal seam inclination;(3)Expansion rate and permeability are declined by exponential function in bilateral sideof gob on the vertical direction. Expansion rate and permeability are first larger, thenprogressively reduced in central part of gob;(4)Coal seam and gob can be divided intofour areas: initial-region, influenced-region, fractured-region, compacted-region.FLUENT software simulates goaf gas distribution using permeability distributionby ABAQUS simulation:(1) High concentrations area of oxygen and lowconcentration area of methane are respectively existence near working face.Themethane concentration is larger on ventilation roadway side than intake airway side;(2) Gas concentration is increased by exponential function at strike direction andlower near ventilation roadway and intake airway reversely.Also gas concentrationgrows faster at the0~50m on the vertical direction;A reasonable layout of boring or drilling is determined and a surface drillingproduction law is revealed:(1) The best location of drilling or surface borehole is30mfrom Ventilation roadway and0~20m from the coal seam roof;(2)Surface boreholedrainage gas flow calculation model is established, discussed the function relationshipbetween permeability and gas extraction radius. Formulas of gas drainage flow indifferent regions are calculated.Jingyuan, Gansu province industrial test of Weijiadi coal mine shows that ifground drilling arrangement within a reasonable position, gas drainage effect is remarkable.1#drilling pure gas1,224,870m3,2#drilling pure gas1,304,600m3and2#drilling gas drainage flow values are compared with the theoretical values.