低渗煤层液态CO2相变射孔破岩及裂隙扩展力学机理

液态CO2相变射孔致裂增透技术作为一种有效的低渗煤层强化抽采方法，已被广泛的应用研究。但由于该技术在破岩及裂隙扩展力学机理方面研究不足，在一定程度上影响该技术进一步发展及应用。基于热工学、弹性力学、断裂力学等理论基础，建立了液态CO2相变气体射流压力模型，理论分析了液态CO2相变射孔破岩力学机理、地应力条件下裂隙扩展力学机理。采用PFC2D离散元颗粒流分析软件，进行数值模拟研究，分析了不同地应力及射流压力条件下液态CO2相变射孔破岩及裂隙分布特征。在以上研究基础上，在川煤集团白皎煤矿进行现场试验，研究表明该技术可有效提高低渗煤层瓦斯抽采效率。

Mechanism of breaking and fracture expansion of liquid CO2 phase change jet fracturing in low-permeability coal seam

Liquid CO2 phase change jet fracturing technology has been widely used and studied as an effective low permeability coal seam enhanced gas extraction method.However,due to the lack of research on the mechanism of coal breaking and crack formation,the further development and application are affected.In this study,based on the theoretical basis of thermal engineering,elastic mechanics and fracture mechanics,a liquid CO2 phase change gas jet pressure model was established.The mechanical mechanism of liquid CO2 phase change jet coal breaking and fracture expansion under in situ stress conditions was analyzed.Then,the PFC2D discrete element particle flow analysis software was used to carry out a numerical simulation.The distribution characteristics of rock cracking fractures by liquid CO2 phase change jet under different in situ stress and jet pressure conditions were analyzed.Finally,on the basis of above research,the field test was carried out in Baijiao Coal Mine.The research shows that the technology can effectively improve the gas drainage efficiency of low permeability coal seam.