Gas hydrates are crystalline compounds which can form under high pressures and low temperatures. In many respects they are alike to porous ice, since they are
clathrate compounds, consisting of an apolar molecule (for example dioxide or hydrocarbon gas) trapped in a "cage" of water molecules linked by hydrogen bonds.

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Natural gas hydrates naturally occur in permafrost, undersea sediments, or in the form of layers on the deep sea floor. As a result, they are now considered as a
potential energy resource for the future, since the reserves are estimated up to two times the total resources of oil+gas+coil.

However they also are a source of worry for the oil industry companies, since drilling into hydrate layers could cause their decomposition in gas and water, and thus
bring about an instabilility in the continental margin, possibly responsible for earthquakes, landslides and subsequent overwhelming. This has since recently given rise
to intensive research in the field of marine geology and cartography.

On the other hand, hydrate crystallisation can be provoked by industrial means. Indeed, they are now considered as a possible solution for gas storage in a solid
form. However, when appearing in an industrial context, gas hydrates are rarely welcome. It is typically the case in offshore oil exploitation, as undersea conditions (a
few tens of bars and 3-4°C in temperature) are sufficient for their formation. Consequences may be the blocking of the oil transmission lines, by plugging valves and
other transport facilities.
 

- crystallographic structure and properties

- methane hydrate equilibrium curve and stability into sediments

- gas hydrates into pipelines