Ultrasonic S-wave indirectly detects the very narrow gap at contact of grains: Glass beads and Ottawa sands

Considerably different from sandstones, sands have point-like contact of grains. In contrast, sandstones have cementation between grains, which has diminished the very narrow gap at contact of grains. In this paper, ultrasonic S-wave in brine-saturated glass beads and Ottawa sands is used to detect the very narrow space at contact of grains. The data of the dry beads/sands and brine are inputted into Biot theory to yield phase velocity of the saturated beads/sands. By fitting the theoretical velocity with the ultrasonic measurement, phase velocity, the quality factor and S-wave permeability are determined as functions of frequency. The predicted ultrasonic quality factors appear to be very close to that of water-saturated Berea sandstone. Our previous study showed that for Berea sandstone, the low-frequency S-wave permeability is approximately half of Darcy permeability. However, for glass beads and Ottawa sands, the S-wave permeabilities at low frequencies are one-order magnitude lower than Darcy permeabilities. This well shows that S-wave permeability of the beads/sands is associated with the very narrow gap at contact of grains which is successfully detected by ultrasonic S-wave in the indirect way.