Gas Hydrates

Methane hydrate morphology on a water droplet with an applied temperature gradient. p = 4.02 MPa

 

Gas hydrates (clathrates) have been studied for two centuries, but only until recently have we realized the enormous implications that these compounds have on our environment and our secure supply of clean energy. Clathrates are crystalline compounds that form when small volatile molecules come in contact with water at low temperatures and high pressures (there are exceptions to this rule of thumb). Hydrates remained an academic curiosity until 1934 when it was corroborated that these compounds plugged natural gas pipelines. Renewed interest in gas hydrates came with the discovery of their occurrence in nature in the 1960’s.

Clean Energy

Conservative estimates suggest that the amount of energy stored in hydrates (as natural gas) is at least twice that of all traditional fossil fuels combined. Most of the natural gas hydrates are found in the oceans in close interaction with marine sediments; however, there is a considerable amount of hydrates found in the permafrost regions. In particular, the Mallik site in the Northwest Territories in Canada has proven that natural gas extraction from a hydrate deposit under the permafrost is possible.
 

  

Environmental

  

Sequestering CO2 as a hydrate in the bottom of the oceans has been proposed as an alternative to reduce increasing atmospheric carbon dioxide concentration. Recently, concerns have been raised regarding the role that natural hydrates could play in global climate change. Hydrates constitute a considerable carbon sink, making them an important part of the organic carbon cycle and sizeable releases of methane due to hydrate destabilization in the ocean floor could exert a significant effect in enhancing global warming. On a more short term basis, oceanic hydrate destabilization could also pose a submarine geological hazard, as industry moves to exploit resources at great depths in the seabed.
 

Gas Storage and Transportation

The possibility of using hydrates for gas storage and transportation has also been put forward. Hydrate energy density is comparable to that of compressed natural gas, but less than that of liquefied natural gas. Hydrate storage and production conditions being much milder than that of compressed and liquefied natural gas, it has been suggested that it would be economical to transport natural gas in hydrated form. More recently, the possibility of using hydrates to store hydrogen has also been suggested.