Methane hydrate formation and dissociation in fine sands at temperatures near 0 oC

In 1996, Canadian and Russian scientists collaborated to construct a laboratory test cell for producing artificially hydrated sediments. This paper presents results from an initial suite of experiments characterizing the formation and dissociation of methane hydrate in fine-grained sand at temperatures near 0iC. Results indicate that P/T equilibrium conditions for hydrate stability in sand are slightly offset from values determined for pure-system hydrates, presumably due to porous media effects. Analyses of P/T response and measurement of gas yields suggest hydration efficiencies approaching 75%, with typical gas yields between 100-150 cm3/g of soil water. Time series measurements reveal the complexity of hydrate formation/dissociation in natural soil media, with hydrate formation occurring over relatively long periods, while dissociation typically is more rapid. Multiple cycles of hydrate formation, freezing, thawing and dissociation suggest considerable influences arising from changes in soil structure and water memory effects.