ACOUSTIC DISPERSION IN POROUS ROCKS

The dispersion of ultrasonic waves by porous rock is studied by investigating the propagation across solid plates of limestone, in the frequency range 30 kHz-1 MHz. In this frequency range, we have observed only a single compressional wave and a shear wave. The slow wave, predicted by the Biot theory, was not detected. Wave speeds increase with increasing frequency from a low frequency limit C0 of the phase velocity to a phase velocity C(infinity) at the nondispersive high frequency limit. The Biot theory used to predict compressional and shear wave velocities, contains numerous parameters. We discuss empirical and theoretical ways to predict values of these parameters for limestone. The comparison. and discussion of the experimental data with the prediction from the Biot theory are presented.