Research On Strengthening Gas Pre-drainage Effect With The Fracturing Technique By Liquid CO₂ Phase Transition In Layer Through Boring

Based on physical blasting, the fracturing technique by liquid CO2 phase transition was easy to use and increased permeability better. Compared with several hydraulic measures and presplitting blasting in deep hole by explosive, the fracturing technique by liquid CO2 phase transition had a better applicability in single low permeability soft seam.Firstly, the article described the structure of the fracturing equipment by liquid CO2 phase transition, and developed the equipment on the basis of ground experiment, to make sure it would play a good role when used underground. Then, the researchers performed the fracturing experiment in layer through boring in 16051 floor roadway in Jiulishan Mine. By measuring the gas flow and gas concentration and other parameter showed that the fracturing technique by liquid CO2 phase transition had an obvious effect of encreasing coal seam permeability. After the experiment, the gas permeability coefficient had enhangced 43.62 times, the average gas flow was 2~9 times of the flow by using the hydraulic flushing, and was 3.5~16.3 times of the flow without any fracture measures in single drill. The attenuation coefficient of gas flow decreased 66.5%, which made gas drainage to be more sustainability.Besides, the article set up a mechanical model according to the percolation theory,theory of conservation of mass,the theory of conservation of energy and effective stress equation. With the help of the numerical simulation software of Comsol Multiphysics, it acquired the effective influencing radius under 270 MPa pressure.Comparing with the results of field test, it determined that the effective influencing radius was 5.0m under the Jiulishan Mine’s existing condition, and studied the reasonable hole arrangement parameters.