Applied Research On Permeability Increasing By Liquid Carbon Dioxide Phase Transition Blasting Based On Different Initiating Condition

For the low permeability coal seam, in addition to hydraulic fracturing technique and deep pre-split blasting measures, it has been developed liquid carbon dioxide phase change blasting technology to improve permeability in recent years, as a new permeability enhancement technology, it has advantages of no sparks produce, pressure control, easy to store and transport and high security and so on.Firstly, carbon dioxide physical properties of liquid phase and gas phase are described. By analyzing the thermodynamics changes in the liquid carbon dioxide blasting process, the paper analyzed energy transformation process of liquid carbon dioxide into gaseous. Then we studied thermodynamic calculation formula on liquid carbon dioxide into gaseous. According to TNT equivalent model, the TNT equivalent of the test tube reservoir was calculated.Second, combined with blasting theory, we analyzed the role of high-pressure carbon dioxide gas on coal fracturing and stress wave propagation process. According to damage and fracture mechanics theory, the paper analyzed the crack propagation process under high pressure gas produced by liquid carbon dioxide blasting, and studied law of the dynamic crack extend.Using finite element analysis software ANSYS_LS_DYNA3D, fracture mechanics theory, we established liquid carbon dioxide blasting fracturing calculation model, simulated the stress field produced by liquid carbon dioxide blasting. By analysis of stress wave propagation in coal after blasting, we studied the fractured and influence effect of different TNT equivalent.Based on the theoretical studies and numerical simulations, we formulated five different liquid carbon dioxide blasting programs which were tested in Changcun 3# coal seam, analyzed the effect of blasting technology., The amount of coal mine methane drainage increase 1.4 to 3.5 times, an average of 2.5 times, after the liquid carbon dioxide phase change blasting, so the effect of permeability increase is remarkable. Meanwhile, Different blasting program to improve gas drainage effect is quite different, based on the scalar extraction data, we can draw that the use of secondary blasting and delay-action blasting programs have more significantly effect to improve the seam permeability.