Research On Key Technology Of Gas Extraction By Large Diameter Drilling In Coal Seam

In the deep coal resource mining stage,the aperture of gas extraction drilling hole is generally 0.042～0.130 m,and its small pore diameter has a poor effect on high gas and low gas permeable coal seam,and there are problems such as low mine gas extraction rate,borehole pre-extraction concentration not up to standard,and long extraction cycle,which in turn causes tension in the working face.In order to solve the above problems,this thesis focuses on the working face of Shunhe Coal Mine,a typical deep underground high-gas lowpermeability coal seam,and uses research methods such as on-hole and downhole investigation,laboratory experiment,theoretical analysis modeling,numerical simulation of COMSOL software,industrial experiment and other research methods to study the key technology of pressure relief and penetration enhancement optimized from small diameter extraction drill hole(0.075m)to large diameter borehole(not less than 0.130 m),and constructs a mechanical model of pressure relief and penetration enhancement of large diameter borehole.The technology scheme of large-diameter borehole pressure relief and permeation enhancement was proposed,and the field test results showed that the coal seam permeation,associated gas and coal resources were safely and efficiently exploited.The main results are as follows:(1)The physical and mechanical parameters of the coal rock sample of the 2404 working face and the characterization of the pore fracture were carried out: the coal seam texture was soft,the air permeability was poor,the roof was a soft rock layer,and the multistage plugging control surrounding rock should be considered during drilling maintenance,the pore ratio before and after compression damage of the coal sample changed greatly,and the expected effect of large-diameter borehole penetration enhancement was considerable.The stress distribution characteristics around the borehole were analyzed,the mechanical model of pressure relief and permeability enhancement of large-diameter borehole was constructed,the stress-strain solution of viscoelastic-plastic deformation of the surrounding rock of the borehole was derived,and the influence of borehole diameter increase and insitu stress on coal disturbance was deeply studied: borehole diameter increase had more obvious factors on coal disturbance,and the influence of in-situ stress on coal disturbance was limited by the borehole wall support resistance Pq(t).The evolution equations of permeability and porosity considering the long-term mechanical effects of coal rock are derived,and a gas-bearing gas-solid coupling model is constructed.(2)The law of pressure relief and penetration enhancement of large-diameter drilling holes is revealed: the gas pressure around large-diameter drilling decreases with the increase of pumping,the vertical stress is closer to the hole core,the peak value is smaller,and the permeability is closer to the hole core,the greater the increase.The effective extraction area judgment index was determined,that is,the coal seam gas pressure did not exceed 0.22 MPa.The single-hole extraction model with different high-diameter ratio and the multi-hole extraction model with different hole spacing were constructed,and the effects of borehole diameter and hole spacing on the effect of coal seam pressure relief and penetration enhancement were analyzed,and the borehole diameter of 0.30 m and hole spacing of 8.0 m for large diameter coal seam at 2404 working face were determined.(3)The permeability effect of coal seam drilling of large diameter coal seam is better than that of ordinary drilling,and the extraction concentration is high and the stability period is long.The effective extraction radius of the large-diameter coal seam extraction drill hole of 180 days of continuous extraction was determined by the pressure reduction method to be slightly higher than 4.0 m,which was not much different from the effective extraction radius of 3.0 m determined by simulation,which further verified the correctness of the gas-bearing gas-solid coupling model.Large-diameter coal seam drilling has a significant effect on coal seam pressure relief and permeability,realizing efficient extraction of gas resources,which is an effective guarantee technology for deep coal and gas co-mining,and further improves the gas treatment technology system,which has reference significance for the prevention and utilization of gas in similar geological mines.This thesis has 46 figures,10 tables and 149 references.