Study On The Extraction Technology Of Low Permeabilty Coal Seam With Carbon Dioxide Phase Transition In Dafosi Mine

The existence of the mine gas seriously restricts the safe production of the coal mine.The gas emission in the thick coal seam with high gas and low permeability is larger during the mining process,especially in the process of coal caving,it is easy to cause gas overrun in the working face,which has a great impact on the safety production of the mine.With the deepening of coal resources mining depth,the stress of the earth will lead to low permeability of coal seam and gas content.Therefore,in the process of deep mining,the gas control of low permeability coal seam is the most important of the gas control at present.Based on the geological and coal seam occurrence conditions in the 40104 working face of Dafosi coal mine,the gas permeability and gas emission of 4#coal seam in Dafosi coal mine are analyzed.According to the mechanical analysis,the permeability coefficient of the fractured coal seam is proportional to the linear fracture rate and the linear density of the fracture.By theoretical method,it is considered that the use of CO2 phase change fracturing technology can effectively increase the permeability of coal seams.Through the numerical simulation model of FLAC3D,a single hole liquid carbon dioxide phase splitting blasting was obtained to enhance the permeability of different coal hardness,different coal seam thickness and different drilling interval.The results of numerical simulation show that due to the close action of ground stress on fractures,the plastic region in the vertical direction is slightly smaller than the horizontal direction;When the hardness f is 0.6?3.2,the blasting effect is the most ideal;When the hole spacing is 4m,the permeability is the best;At the same time,the simulation results provide a reliable basis for the layout of underground industrial test parameters.Monitoring and display through the underground industrial experiment data,the gas permeability increased by 11.2 times after fracturing the coal seam by using the CO2 phase change fracturing technique,and the effective radius of gas extraction was increased greatly,and the gas extraction concentration and the pumping purity were greatly increased.The application of carbon dioxide phase change fracturing technology ensures the gas drainage problem of low permeability coal seam in Dafosi coal mine,and provides theoretical and technical reference for other similar mines.