Application on permeability improvement technology with CO2 phase change to borehole drilling along coal seam

In order to improve the gas drainage effect in the soft, low permeability and high gassy seam under the karst geology condition, based on Guizhou Lyuta ng Mine as the study object, the seam pressure released and permeability improved technology with a CO2 phase change fractured borehole drilling along the seam wa s provided. The paper had an analysis on the seam failure characteristics under the splitting effect of the CO2 fracturing transient gas, including the crack unstability an d diffusion characteristics and the high pressure wave splitting mechanism. The results of the permeability improved test with the CO2 fractured borehole dilling along t he seam showed that the permeability effect of the CO2 fracturing borehole drilling technology along the seam was obvious, after the fracturing in the area, the seam pe rmeability was increased by five times and the attenuation coefficient was reduced by 53. 6%. The gas drainage concentration was increased by three times and the av erage drained gas volume fraction was about 70%. Under the condition of the same gas drainage time, the residual gas content in the seam was obviously reduced and the gas drainage rate was about 55%. In No. 6 medium seam of the Mine, the period of the previous gas drainage target was about 6 ~ 12 months and after the fracturi ng, the period of the gas drainage target was 1 ~ 2 months. The overall gas drainage efficiency was increased by six times and the period of the gas drainage target wa s highly reduced.