Acoustic emission characteristics and the energy distribution of the shale in Brazilian splitting testing

To explore the mechanical properties and the acoustic emission(AE)characteristics of shale with different bedding angles, the failure mode of shale with different bedding angles was analyzed by using Brazilian splitting testing, AE technique and 3DEC numerical simulation.The results show that the tensile strength of shale exhibits obvious anisotropic behavior due to the obvious bedding structures in shale.The stress-time curves obtained from Brazilian splitting testing can be divided into three main stages.At the lower bedding angles, the cumulative AE events-time curves exhibit a flat to sharply rising trend; while at the higher bedding angles, the cumulative AE events-time curves exhibit "multiple steps" characteristics.The failure modes of shales are closely related to the bedding angle, and the failure patterns obtained from the Brazilian splitting tests are consistent with the results of 3DEC numerical simulation.The AE energy probability density P(E) distribution curves of all shale specimens were fitted well with the power law function.Bedding angles in shale did not change the scale invariance of AE energy in the process of Brazilian splitting testing.The critical parameters of the AE energy probability density distribution curve at bedding angle of 90° is the largest, and the proportion of AE signals is getting larger at the low energy range.The critical parameters of AE energy probability density distribution curve can be used to characterize the damage degree of the shale in the process of Brazilian splitting testing.The results are of some significance for the reservoir stimulation design in shale gas development.