Abstract To evaluate the crack initiation and propagation behavior during pulsating hydraulic fracturing (PHF) process, lab tests on PHF of coal samples were performed by using a self-developed true triaxial testing system. The results demonstrate that: the crack could be better developed under pulsating hydraulic load. And as PF increase, the initiation pressure decreases firstly, then increases and reached minimum when the PF is 4 Hz. Besides, the changes of acoustic emission (AE) behavior can be divided into four stages: quiet phase, acceleration phase, lifting phase and resting phase. And the accumulated energy of acceleration and lifting phase increased respectively about 4.81 and 17.21 times (average) in comparison with quiet phase. Our results also show that the proportion of minor AE events and great AE events were higher in acceleration phase, and lifting and resting phase respectively. And when the PF is 4 Hz, the proportion of smaller AE events is larger.

中文翻译：

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煤层气储层脉动水力压裂裂缝动态演化实验研究1

摘要 为了评估脉动水力压裂（PHF）过程中裂纹的萌生和扩展行为，利用自主研发的真三轴测试系统对煤样的PHF进行了室内测试。结果表明：在脉动水力载荷作用下，裂纹能更好地发展。并且随着PF的增加，起爆压力先减小，然后增大，当PF为4Hz时达到最小值。此外，声发射（AE）行为的变化可分为四个阶段：安静阶段、加速阶段、提升阶段和静止阶段。加速阶段和提升阶段的累积能量分别比安静阶段增加了约4.81倍和17.21倍（平均值）。我们的结果还表明，在加速阶段、举重和休息阶段，轻微 AE 事件和大 AE 事件的比例更高。而当PF为4Hz时，较小的AE事件所占的比例较大。