Acoustic Emission and Failure Characteristics of Shales with Different Brittleness Under AWJ Impingement

To determine the effect of shale brittleness on the failure and acoustic emission (AE) characteristics under abrasive waterjet (AWJ) impingement, we performed fixed-point AWJ perforation trials on three shales with different brittleness. AE sensing and time–frequency analysis were employed to detect shale failure mechanisms involved in AWJ perforation. Results indicate that there is a positive correlation between the penetration rate and shale brittleness, but a negative correlation between AE energy and shale brittleness. For high-brittleness shale in which inter-granular cracking dominates material removal, AE signal shows lower amplitude, lower root mean square, and smaller integral area of power spectra density (PSD), and the high-pass filtering (HPF) component of AE signals tends to be a continuous type. In contrast, trans-granular cracking plays a more dominant role in low-brittleness shale failure, and the corresponding HPF AE signal is characterized by continual burst emission events. PSD area is negatively correlated with erosion depth of AWJ.