煤岩径向井-脉动水力压裂裂缝扩展规律与声发射响应特征

径向井-脉动水力压裂是一种煤层高效增透新方法。利用声发射仪和伺服式脉冲疲劳试验机，开展了煤岩径向井-脉动水力压裂室内实验。基于广义关联积分分形维数计算方法与型煤岩样声发射信号响应特征，分析了压裂过程中微裂缝发育特点和宏观裂缝扩展规律，探究了径向井分支数、长度、脉动频率和振幅等参数对压裂效果的影响规律。实验结果表明，低压脉动压裂阶段声发射信号相对分散，脉动能量促使微裂缝发育；高压脉动压裂阶段声发射信号相对集中，脉冲能量促使主裂缝快速延伸；呈非对称展布的径向井眼数量越多、长度越长，煤岩增透效果越好。实施径向井-脉动水力压裂时应控制初始脉动压力低于煤岩起裂压力，适当延长低压脉动作用时间，使微裂缝在近井地带充分发育，以降低主裂缝延伸压力，形成更大尺度宏观裂缝。

Fracture propagation laws and acoustic emission response characteristics of coal radial well-pulse hydraulic fracturing

Radial well-pulse hydraulic fracturing is novel stimulation method for coalbed methane. The acoustic emission detector and servo pulse fatigue test machine were used to conduct laboratory experiments on the coal radial well-pulse hydraulic fracturing. Based on the fractal dimension calculation of generalized correlation integral and the response characteristics of acoustic emission signals from briquette rock samples, this study analyzed the micro-fracture development characteristics and macroscopic fracture propagation laws in the fracturing progress, and explored the influence laws of several parameters, such as branch number, length, pulse rate and vibration amplitude of radial well, on fracturing effects. The experimental results show that the acoustic emission signals in the low-pressure pulse fracturing stage are relatively dispersal, and the pulse energy can improve the micro-fracture development. However, in the high-pressure pulse fracturing stage, the acoustic emission signals are relatively concentrated, and the pulse energy can accelerate the propagation of major fracture. The more the radial well boreholes with dissymmetrical distribution are, and the longer the boreholes are, the better the stimulation result will be. During the radial well-pulse hydraulic fracturing, the initial pulse pressure should be lower than initial fracturing pressure of coal rocks, and the appropriate extension of low-pressure pulse time leads to the full development of micro-fracture in the near-wellbore region, so as to reduce the extension pressure of major fracture and form larger macroscopic fractures.