The nucleation and failure processes of a fine-grained organic-rich rock (shale) are investigated by means of acoustic emission (AE) technique and ultrasonic velocity measurements. The rock sample was collected from the Kakwa field of the Montney play in Canada, and was loaded into a triaxial geophysical imaging cell under a confining pressure of 10 MPa. The macroscopic shear slippage generated numerous AE events, which were processed and studied for fracture propagation. Detailed analysis based on AEs and ultrasonic velocity surveys include deformation-induced velocity anisotropy, source hypocenter determinations, moment tensor inversion, and stress inversion. Results show that AE events were all triggered around the peak stress and that a large stress drop occurred. Through hypocenter location analysis, a spatial correspondence of AE clusters and the shear band imaged by CT scan was found. Moment tensors revealed failure mechanisms of the shale specimen. Distinct characteristics of the AE activity in Montney shale were identified showing different failure behavior from granite. These differences could arise from the low brittleness and stiffness of shale.
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