Introduction And Background 11 Why study synthetic gas hydrates

Gas hydrates are an intriguing class of nonstoichiometric compounds that have significant commercial and scientific applications both as an energy resource and as a manufactured material. The last half-century has witnessed a marked escalation in the scope of experimental research on gas hydrates, particularly directed towards the determination of their phase equilibria, formation kinetics, crystallographic and structural properties, transport and thermal properties, effects of inhibitors, and a number of related geochemical topics.

There remains, however, a paucity of reliable experimental measurements of many of the physical, material, thermal, acoustic, and elastic properties of most pure, end-member hydrocarbon hydrates. Instead, either water ice, or hydrates readily formed in the laboratory but rarely occurring in nature (such as ethylene-oxide hydrate and THF hydrate), have commonly been used as analogue material for property measurements. Consequently, there does not exist an accurate and comprehensive database of physical and material properties for end-member gas hydrates, and particularly for those hydrates that are more problematic to form and stabilize in the laboratory. Compounding this problem is the difficulty in retrieving pristine material from natural settings on which to make such measurements, in different laboratories using different methods, and in the general lack of agreement of measurements made on synthetic material.

A wide variety of processes and techniques have been used to synthesize gas hydrates in the laboratory, each yielding a final product that may be highly suitable for some types of experimental testing while clearly unsuitable for others. Here, we focus on laboratory production of pure, poly crystalline methane hydrate and hydrate-sediment aggregates that are suitable for a variety of physical and material properties measurements made on pure, end-member

material. The methods described here are based on a materials-science approach that strives to produce final test specimens with highly-reproducible composition, texture, and grain characteristics. Property measurements on such test specimens not only provide end-member material characterization, but also aid in the interpretation of similar measurements made on more complicated hydrate-bearing material retrieved from natural settings.

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