Influence of Stress on Elastic Wave Velocity Around a Borehole in Rocks

Abstract eng:
In this paper, we introduce acoustoelasticity theory to investigate wave-velocity distribution and polarization around a borehole in prestressed rocks to build their direct and explicit link macroscopically. The acoustoelasticity theory based on non-linear continuum mechanics invokes third-order elastic constants to explain the stress-induced wave-velocity change of rocks. The numerical results show that directions of the maximum and minimum wave-velocity change around a borehole correspond to those of the minimum and maximum far-field principal rock stresses, respectively. In order to validate the theoretical analysis, wave velocities around a borehole in sand stone under the biaxial loading are measured by pulse-echo method. The detail discussion shows that the experimental results coincide with the theoretical results, which means that the ultrasonic method based on acoustoelasticity theory could be a promising measurement method for in-situ rock stresses.

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