Study on the Cracking and Penetration Effect of Liquid Carbon Dioxide Phase Transition

Low permeability coal seams severely restrict the safe, efficient and rapid development of coal mines. Cracking associated with carbon dioxide phase changes is of great significance for improving the permeability of coal seams and the gas drainage rate. Taking a particular mine as an example, technology that increases liquid carbon dioxide phase change and permeability is used to fracture the coal seam. Then, quantitative analysis of the fracture characteristics of the coal seam is performed, and the gas content, extraction concentration, and excavation after fracturing are monitored and studied. The results show that the liquid carbon dioxide in the coal seam has a permeability enhancement radius of 2 m after phase cracking. After phase cracking, the number of coal seam cracks and the width of the coal seam cracks is increased. The rate of gas content decline is significantly higher than that before cracking. After cracking, the gas concentration is significantly improved and can be maintained at approximately 50% for a long time, and the extraction purity is significantly higher than that before cracking. The tunnelling standard increases from 8 m/d before cracking to 9.1 m/d after cracking; thus, cracking promotes the speed of tunnelling.