Shock-induced borehole waves in porous formations: Theory and experiments

The characteristics of the pseudo-Stoneley wave along boreholes in porous formations are studied in a broad band of frequencies (100 Hz–200 kHz). Experiments are performed using a shock tube technique to excite the pseudo-Stoneley wave in a water saturated confined reservoir. The formation is a natural Berea sandstone. Frequency-dependent phase velocities and damping coefficients are measured using this technique. Quantitative agreement between the experimental results and the theoretical predictions is found for the phase velocity in the frequency range from 10 to 50 kHz. Theoretically, the influence of the permeability on the phase velocity, attenuation, radial displacement, and pore pressure is studied on the basis of the Biot theory and the contribution of the different bulk modes to the average radial displacement is analyzed in the frequency domain. The numerical results indicate that the permeability dependence at low frequencies is caused by the Biot slow wave.