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

Abstract

Abstract. 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 refrigerant R11 (CC13F) at 2øC and atmospheric pressure. Measurements were performed on two types of initially unconsolidated sand packs with average grain size 100 [tm and 280 [tm, respectively. P wave velocities varied from about 1700 m/s at low hydrate content to 3810 m/s at a calculated hydrate fraction in the pore space equal to 0.52. S wave velocities were only detectable at hydrate fractions larger than 0.35, where S wave velocities up to 2230 m/s were measured. Our measurements indicate that acoustic measurements are not sensitive to small amounts of hydrate in a system of initially unconsolidated sand. The data show a very distinct change in behavior when the hydrate fraction exceeds 0.35, the concentration at which hydrate cementation of the sand grains is believed to occur. Measurements for samples without sand (samples containing water, R11, and hydrate) are also reported. For hydrate with6ut 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.

A laboratory investigation into the seismic velocities of methane gas hydrate‐bearing sand

“…Pearson et al [1986] undertook velocity measurements while using THF as a hydrate former and reported V p of 4500 m s À1 (for a hydrated sandstone) while Kunerth et al [2001] reported V p of 3400 m s À1 (for a hydrated sand). Berge et al [1999] reported both V p and V s as a function of hydrate pore saturation in sands using Freon-11. They found that below a critical hydrate concentration within the pore space $35%, V p was not significantly affected and V s was unable to be measured.…”

“…[8] Because of the difficulty in forming methane gas hydrate, differing hydrate formers have been used such as propane [Stoll, 1974;Stoll and Bryan, 1979;Stoll et al, 1971], and analogues of natural gas including tetrahydrofuran (THF) [Bathe et al, 1984;Berge et al, 1999;Kiefte et al, 1985;Kunerth et al, 2001;Pearson et al, 1986] and Freon-11 (CCL 3 F) [Berge et al, 1999], all of which require less onerous stability conditions. These compounds form structure II gas hydrates which have different crystal structure to methane hydrate (structure I), which may lead to differing mechanical properties.…”

Are Laboratory-Formed Hydrate-Bearing Systems Analogous to Those in Nature?

“…Noncementing pore-filling hydrate grows freely in the pore space without contact to the sediment grains. At a certain hydrate saturation (25 % to 40 %), 25,26 it starts to build bridges between neighboring grains and becomes load-bearing and grainsupporting, respectively. Another modeling approach avoids the consideration of different hydrate habits using the patchy saturation concept 27 to estimate the influence of hydrate saturation on physical rock properties.…”

Challenges, Uncertainties, and Issues Facing Gas Production From Gas-Hydrate Deposits

“…Compressional (P-) and shear (S-) wave speeds have been measured in a variety of medium/hydrate combinations. Berge et al (1999) measured P-and S-wave velocities of Refrigerant 11 hydrate in two sands at 2C. No S-waves were detected below hydrate saturations of 35%.…”