The acoustic techniques for estimating the in-situ stresses from downhole tools are being validated for sandstone, limestone (including chalk), and shale in an experimental laboratory setup using large cubic samples of each rock type subjected to stress-induced anisotropy. The experiments involve the measurement of: acoustic velocities (compressional and shear wave); radial, axial and transversal strains; and the corresponding displacements around the borehole along directions parallel and perpendicular to the applied stresses. We show that the stress magnitudes measured at the wellbore wall vary considerably depending on the type of rock being tested and thus velocities have to be calibrated according to rock type to take into account the specific rock mechanical properties and their stress anisotropy dependence when stresses are estimated from the compressional and shear wave velocities in and around the borehole. Our experimental results also show that the measured induced tangential compressive stresses at the borehole for the tested rock materials were found to be nonlinearly correlated with the external applied stress at the boundary. As a result, assumptions of a borehole stress concentration factor of 3 based on Kirsch's equations for a uniaxial stress field may under or over estimate the actual induced compressive stresses at the borehole wall in rocks. The applied boundary stress level at which tensile failure and breakouts occur in the borehole is observed to be correlated with the measured tensile strength from Brazilian tests and the uniaxial compressive strength of each tested rock, respectively.

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