Oceanic Gas Hydrate

Abstract

Many gas hydrates are stable in deep-ocean conditions, but methane hydrate is by far the dominant type, making up >99% of hydrate in the ocean floor (Chapter 2). The methane is almost entirely derived from bacterial methanogenesis, predominantly through the process of carbon dioxide reduction. In some areas, such as the Gulf of Mexico, gas hydrates are created by the rmogenically-formed hydrocarbon gases, and other clathrate-forming gases such as hydrogen sulfide and carbon dioxide. Such gases escape from sediments at depth, rise along faults, and form gas hydrate at or just below the seafloor, but on a worldwide basis these are of minor volumetric importance compared to microbial and the rmogenic methane. Methane hydrate exists in several forms in marine sediments. In coarse grained sediments it often forms as disseminated grains and pore fillings, whereas in finer silt/clay deposits it commonly appears as nodules and veins. Gas hydrate also is observed as surface crusts on the sea floor. Methane hydrate samples have been obtained by drilling.