High efficient gas drainage principle and application of low permeable seam with CO _2 pre-fracturing and permeability improvement

In order to solve the low gas drainage efficiency,long gas drainage time and other problems of the low permeable seam,the CO_ 2 high energy pre-fractur ing and permeability improved technology was applied to reconstruct the low permeable seam,to improve the seam gas permeability and to improve the gas drainage vo lume and gas drainage efficiency.With the analysis on the pressure releasing and permeability improved mechanism of the high energy gas pre-fracturing and permeabil ity improved technology for the low permeable seam,a gas drainage technology plan with the high energy gas pre-fracturing and permeabilty improvement was set up f or the coal mining face and the excavated face.The site experiment and effect of the technology were analyzed.The results showed that the high energy gas pre-fracturi ng could form a crack and pressure released ring or the crack and pressure released zone in the seam and thus the seam permeability and gas desorption speed within the ring(zone) was improved.After the pre-fracturing and permeability improved of the gateway driving face,the average gas drainage concentration,average gas draina ge pure flow and average gas drainage pure flow per 100 m borehole were individually increased by 1.5 times,4.7 times and 17.8 times.After the pre-fracturing and per meability improved of the coal mining face,the average gas drainage concentration,the average gas drainage pure flow and the average gas drainage pure flow per 100 m borehole were increased by 0.8 time,1.0 time and 1.5 times individually.