In order to obtain fundamental data for the evaluation of permeability in methane hydrate reservoir, we have conducted an experimental study on the behavior of multiphase flow in artificial sample of marine sediment with gas hydrates. The formation rate of methane hydrate in porous media depends on the diameter of sand and the kind of porous media. In an experiment of dissociation of hydrate by the injection of hot water, the increase of permeability in methane hydrate reservoir was observed as a function of time. Furthermore, it was found that the water permeability drastically decreases as the hydrate saturation becomes higher.
Gas hydrates is one of the potential resources of natural gas in the near future, because the large amount of reservoir exists in marine sediments or in permafrost regions worldwide. It is very important to understand the porous media flow in marine sediments with gas hydrate formation, especially for developing the extraction system for gas hydrates, and in considering the environmental impacts due to the development. Unusual multiphase flow may cause the change in stability of seafloor, and result in the emission of natural gas into marine environment. Some extraction methods of gas hydrates from the reservoir in marine sediments has been proposed, such as depressurization, thermal stimulation and inhibitor injection. These are all based on the in-situ dissociation process of gas hydrates that is transformed into methane gas and water. Only methane gas can be produced from the reservoirs in marine sediments. It is very important to estimate the properties and the permeability of hydrate reservoir in such situations as dissociation and consolidation. In this study, we have carried out an experiment for observing the physical phenomena of gas-water multiphase flow in porous media and for clarifying the properties of formation and dissociation of gas hydrates.
