Technology and Equipment of Three Dimensional Rotation Water-jets Enlarging Bore to Improve Coal Seam Permeability

According to high gas extraction difficulty of the low permeability seam, a new technology of three dimensional rotation water-jets enlarging bore technology for seam permeability improvement was developed. With the theoretical analysis, numerical simulation and site tests, the study results showed that three dimensional rotation water-jets breaking coal was given priority to shear breakage, reasonably layout enlarging borehole can realize regional gas control. The underground test results of Pansidong Mine showed that gas concentration of enlarging borehole was 80.5%, the flow of pure drilling gas was 18.15 L/min,respectively 1.43 times that the conventional drilling,pure gas flow rate is 1.72 times that of the conventiond drilling,increa sed by 72%,the gas concentration and the flow of pure drilling gas were highly improved.