Measured acoustic wave velocities of R11 (CCl3F) hydrate samples with and without sand as a function of hydrate concentration

We report acoustic laboratory measurements on initially unconsolidated sand packs with hydrate formation taking place in the pore space. Both P and S wave velocities were measured. Hydrate was formed from water and the refrig erant R11 (CCl3F) at 2 degrees C and atmospheric pressure. Measurements wer e performed on two types of initially unconsolidated sand packs with averag e grain size 100 mu m and 280 mu m, respectively. P wave velocities varied from about 1700 m/s at low hydrate content to 3810 m/s at a calculated hydr ate fraction in the pore space equal to 0.52. S wave velocities were only d etectable at hydrate fractions larger than 0.35, where S wave velocities up to 2230 m/s were measured. Our measurements indicate that acoustic measure ments are not sensitive to small amounts of hydrate in a system of initiall y unconsolidated sand. The data show a very distinct change in behavior whe n the hydrate fraction exceeds 0.35, the concentration at which hydrate cem entation of the sand grains is believed to occur. Measurements for samples without sand (samples containing water, R11, and hydrate) are also reported . For hydrate without sand, P wave velocities ranged from about 1400 m/s at very low hydrate content to about 2500 m/s at a measured hydrate fraction equal to 0.68. For these samples, reliable S wave data were not detected.