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Encyclopedia > Methane hydrate
"Burning ice". Methane released by heating burns, water drips. Inlay: chlatrate structure.Source:
"Burning ice". Methane released by heating burns, water drips. Inlay: chlatrate structure.
Source: USGS

Methane clathrate hydrate is a form of water ice that contains a large amount of methane within its crystal structure. Originally thought to occur only in the outer regions of the solar system where temperatures are low and water ice is common, extremely large deposits of methane clathrates have been found under sediments on the ocean floors of Earth. Methane clathrates are common constituents of the shallow marine geosphere, and they occur both in deep sedimentary structures, and as outcrops on the ocean floor. Methane hydrates are believed to form by migration of gas from depth along geological faults, followed by precipitation, or crystallization, on contact of the rising gas stream with cold sea water.


Methane clathrates remain stable at temperatures up to 18 C. The average methane clathrate hydrate composition is 1 mole of methane for every 5.75 moles of water, though this is dependent on how many methane molecules "fit" into the various cage structures of the water lattice. The observed density is around 0.9 g/cm3. One liter of methane clathrate solid would therefore contain, on average, 168 liters of methane gas (at STP).


Natural deposits

Enlarge
Worldwide distribution of confirmed or inferred offshore gas hydrate-bearing sediments, 1996.
Source: USGS

The combination of low temperature and high pressure found at the bottom of Earth's oceans makes methane clathrates very stable. It is thought that as much as 20 times the current known reserves of natural gas may be contained within ocean-floor clathrate deposits, representing a potentially important future source of fossil fuel that scientists believe could serve as earth's main energy source for hundreds or thousands of years. The chief problem in using methane clathrate commercially is detecting it.


Inferred quantities of methane hydrates exceed those of all other fossil fuels combined, including oil, conventional natural gas and coal IEA WEO 2001, pdf, p.395 (http://www.iea.org/textbase/nppdf/free/2000/weo2001.pdf).


Technology for extracting methane gas from the hydrate deposits in commercial quantities has not yet been developed. A research and development project (http://www.mh21japan.gr.jp/english/mh21/02keii.html) in Japan is targeting commercial-scale technology by 2016.


Climate change

Sudden release of methane clathrate has been hypothesized as a cause of past climate changes, because methane is a greenhouse gas. Two events possibly linked in this way are the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum.


External Links

  • Geological Research Activities with U.S. Minerals Management Service - Methane Gas Hydrates (http://geology.usgs.gov/connections/mms/joint_projects/methane.htm|USGS)
  • IFM-GEOMAR, Kiel, DE (http://www.ifm-geomar.de/|) Burning ice picture (http://www.ifm-geomar.de/index.php?id=gh-allgemein&L=0|)
  • Methane Hydrates (http://www.ornl.gov/info/reporter/no16/methane.htm) - discusses U.S. government funding of methane hydrates research
  • A research and development project (http://www.mh21japan.gr.jp/english/mh21/02keii.html) in Japan

  Results from FactBites:
 
Methane - Wikipedia, the free encyclopedia (1033 words)
The strength of the carbon-hydrogen covalent bond in methane is among the strongest in all hydrocarbons, and thus its use as a chemical feedstock is limited.
Methane is typically found on Earth, when not in gas deposits, in methane hydrate deposits under high pressure under the deep abyssal plains of oceans, produced from the decay of sinking biotic materials at shallow levels.
Methane is the main gas that is released by mud volcanoes, eventually accompanied by helium, nitrogen and brines with bromine, iodine and liquid bitumen.
  More results at FactBites »

 
 

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