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Physical Properties |
IKU, N-7034 Trondheim, Norway
In slow formations, where the shear velocity is lower than the mud compressional velocity, several indirect methods have been used to estimate shear velocity from full waveform acoustic logs. These methods include Stoneley wave velocity and inversion of refracted P-wave amplitude. In this paper we show that in addition to the methods previously reported, the amplitude of the leaky pseudo-Rayleigh waves may in some cases be strongly dependent on the shear wave velocity of the formation. Numerical analysis has shown that there is also some dependence on the velocity and attenuation of the mud, and the borehole radius, whereas the amplitude of the leaky pseudo-Rayleigh waves is quite insensitive to the compressional velocity of the formation and the intrinsic anelasticity of the formation. The predictions have been confirmed by model experiments in a slow formation. It is felt that the effect may be a useful tool, for example, in the study of stress dependent velocities around a borehole.
