Laboratory P-wave measurements in dry and saturated sand

Abstract

We measure the P-wave velocity in a clean medium sand subject to very low stress in a large-scale laboratory cross-hole experiment for frequencies less than 10 kHz. In dry sand the velocity is depth-, and therefore, stress-dependent according to a power law. The velocity in partially saturated sand is essentially the same as in dry sand, which confirms the analytical result of the Biot–Gassmann theory. At 100% saturation, the velocity largely exceeds that in dry and partially saturated sand, once again in accordance with the Biot–Gassmann theory. However, the theory under-predicts velocities by up to 12% in some cases at full saturation. The maximum attenuation determined from spectral analysis of the measured signals closely matches the characteristic frequency predicted by the Biot model.