A Experimental Study On CO₂ Cracking And Penetration Enhancement Technology In Low Permeability Coal Seam Of Guizhou

CO₂ cracking enhanced technology is a new type of coal seam anti permeability technology.The technology belongs to physical high-pressure gas explosion,and has the advantages of no sparking,simple operation,high safety and high efficiency.It can be well applied to high gas and low permeability coal seam.In this paper,it analysed the effect of CO₂ cracking and antireflection Technology,and studied the effectiveness of this technology on gas extraction,by contrasting the phenomenon before and after fracturing of Honglin coal mine and Hongfa coal mine.The main research contents are as follows:First,this paper introduced the microscopic characteristics of low permeability coal seam and the theoretical study on crack growth of coal after cracking.The part of microscopic feature established theoretical basis for the following micro experiment of coal body before and after cracking,by analysing the structural characteristics of the coal body from the pore system and the fracture system,and introducing the research method of pore and fissure of coal body.The part of theoretical study on crack growth of coal after cracking is the fracture criterion to analysis the composite fracture under the influence of far field stress,internal pressure of high pressure gas and gas action.Second,through the low temperature liquid nitrogen test on micropore and fracture structure of samples the samples before and after cracking in Honglin coal mine and Hongfa coal mine,it analysed the adsorption quantity linear and adsorption quantity of isothermal absorption/desorption isotherms and adsorption capacity,and measured the microcosmic parameters of the specific surface area,pore size and pore volume of the sample,and compared the parameters of the samples.The result shows that the microcosmic parameters of specific surface area,pore size and pore volume increased 2³ times more than those before cracking.The development of the crack in the coal body before and after the cracking of the sample was analyzed by the scanning electron microscope.And the result shows that the coal sample after the cracking was larger than the coal sample before the crack,with the pore size larger,the crack widened,and the connectivity of the pore and the fissure better.Finally,to study the effect of CO₂ fracturing technology on gas extraction in low permeability coal seam in Guizhou,this paper chose Hongfa coal mine 1903tailentry as research object to carry out CO₂ fracturing antireflection cracking application engineering test and effect analysis.The study shows that the permeability coefficient of the coal seam was 3.05 times as high as that of the original coal seam,and the permeability of the coal seam was greatly improved.Drilling hole gas emission intensity attenuation reduced 3.35⁸.29 times.The average extraction concentration of coal seam gas has increased by 4.19 times,and the average extraction purity was 3.99 times as much as that of the original coal seam.In the field of drilling gas extraction rate,the effect of gas extraction by single hole is increased by 2.58³.92 times.The workload of drilling was reduced by 4 times,the extraction time was shortened by 55 days,the gas emission was reduced by 40%,and the coal seam gas extraction efficiency was remarkable.The CO₂ fracturing technology provides reference for solving the problem of gas extraction technology in low permeability coal seam in Guizhou mining area.