Research on key technologies for reasonable sealing depth of gas extraction drilling
For the outburst mine of a single main coal seam,the outburst measures of pre-pumping coal seam gas are mainly used in the extraction drilling,and the reasonable sealing depth of the pumping drilling is the key factor to ensure efficient pumping,once the drill-ing sealing depth is not enough,resulting in the drilling leakage and the sealing hole fails,which will seriously affect the work efficiency of the entire extraction system and the safety production of coal mine.Regarding this issue,the acoustic wave method was used to test the loose zone of the rock roadway,and the development range of the"three zones"of stress in the rock roadway was simulated by FLAC3D numerical method;the field test of the loose circle of the coal roadway was carried out by the drill cuttings method,and the de-velopment range of the"three zones"of stress in the coal roadway was investigated;on the basis of theoretical analysis of the initial sealing depth of drilling,on-site optimization experiments on the initial sealing depth of drilling were carried out.Research shows the range of the loose zone of the rock roadway measured by the acoustic wave method was 4.4-4.7 m,which was basically consistent with the FLAC3D numerical simulation result of 4.2 m;according to the variation law of the measured values of the"three zones"of stress in the coal roadway based on the drill cuttings index,the range of the pressure relief zone of the coal roadway was determined to be 10 m from the orifice.Based on the stress distribution of the"three zones"in the roadway,the reasonable initial sealing depth for cross layer drilling and parallel layer drilling was determined,and on-site experimental investigation was carried out.The initial sealing depth was avoided from the pressure relief zone,and the pumping effect was greatly improved.
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