Hydrate formation in an unsaturated system-Impacts of fine particles and water content

Parametric study of hydrate saturation dependent properties of hydrate-bearing sediments requires a large amount of uniform and representative specimens. Expedited synthetization of hydratebearing sediments in the laboratory usually uses an unsaturated system due to low methane solubility in water. This study experimentally investigates how various factors affect the distribution of formed hydrate in the sediments via X-ray computed tomography. Results show that the pressure-temperature history is the most critical factor influencing water migration during hydrate formation. Hydrate formed by cooling-pressurization method tends to lead to preferred hydrate formation at core boundaries where exothermic heat can be easily dissipated. The presence of fine-grained particles fails to mitigate this phenomenon, but can effectively suppress water migration even when hydrate is formed using the pressurization-cooling method or the freezingpressurization-thawing method. Fine-grained particles reduce water activity which further reduce the amount of hydrate formed in the system. The mixing sequence of sand-clay-water mixture affects the final morphology and distribution of each phase and eventually affects hydrate distribution in the sediments. A small amount of clay in sands can suppress water preferentially residing at grain contacts and combine with water acting as a pore filling component. This potentially helps synthesize non-cementing hydrate-bearing sediments in the laboratory more efficiently.

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