The world's largest natural gas resource is trapped beneath permafrost and ocean sediments.
The Next Energy "Game Changer"?
As natural gas from shale becomes a global energy "game changer," oil and gas researchers are working to develop new technologies to produce natural gas from methane hydrate deposits. This research is important because methane hydrate deposits are believed to be a larger hydrocarbon resource than all of the world's oil, natural gas and coal resources combined.  If these deposits can be efficiently and economically developed, methane hydrate could become the next energy game changer.
Enormous amounts of methane hydrate have been found beneath Arctic permafrost, beneath Antarctic ice, and in sedimentary deposits along continental margins worldwide. In some parts of the world they are much closer to high-population areas than any natural gas field. These nearby deposits might allow countries that currently import natural gas to become self-sufficient. The current challenge is to inventory this resource and find safe, economical ways to develop it.
What is Methane Hydrate?
Methane hydrate is a crystalline solid that consists of a methane molecule surrounded by a cage of interlocking water molecules (see image at the top of this page). Methane hydrate is an "ice" that only occurs naturally in subsurface deposits where temperature and pressure conditions are favorable for its formation. These conditions are illustrated in the phase diagram on this page.
If the ice is removed from this temperature/pressure environment, it becomes unstable. For this reason methane hydrate deposits are difficult to study. They cannot be drilled and cored for study like other subsurface materials because as they are brought to the surface, the pressure is reduced and the temperature rises. This causes the ice to melt and the methane to escape.
Several other names are commonly used for methane hydrate. These include: methane clathrate, hydromethane, methane ice, fire ice, natural gas hydrate, and gas hydrate. Most methane hydrate deposits also contain small amounts of other hydrocarbon hydrates. These include propane hydrate and ethane hydrate.
Where Are the Methane Hydrate Deposits?
Four Earth environments have the temperature and pressure conditions suitable for the formation and stability of methane hydrate. These are: 1) sediment and sedimentary rock units below Arctic permafrost; 2) sedimentary deposits along continental margins; 3) deep-water sediments of inland lakes and seas; and, 4) under Antarctic ice. . With the exception of the Antarctic deposits, methane hydrate accumulations are not very deep below Earth's surface. In most situations the methane hydrate is within a few hundred meters of the sediment surface.
In these environments methane hydrate occurs in the sediment as layers, nodules, and intergranular cements. The deposits are often so dense and laterally persistent that they create an impermeable layer that traps natural gas moving upwards from below.
In 2008, the United States Geological Survey estimated the total undiscovered gas hydrate resource for the Alaska North Slope area. They estimate that the total undiscovered natural gas resource in the form of gas hydrate ranges between 25.2 and 157.8 trillion cubic feet. Because very few wells have been drilled through the gas hydrate accumulations, the estimates have a very high level of uncertainty. 
Where is Methane Hydrate Produced Today?
To date there has been no large-scale commercial methane production from gas hydrate deposits. All of the production has either been small scale or experimental.
In early 2012, a joint project between the United States and Japan produced a steady flow of methane by injecting carbon dioxide into the methane hydrate accumulation. The carbon dioxide replaced the methane in the hydrate structure and liberated the methane to flow to the surface. This test was significant because it allowed the production of methane without the instabilities associated with a melting gas hydrate. 
The most likely methane hydrate deposits to be selected for first development will have the following characteristics: 1) high concentrations of hydrate; 2) reservoir rocks with high permeability; and, 3) locations where there is an existing infrastructure.  Deposits meeting these characteristics will likely be located on the Alaska North Slope or in northern Russia.
Methane Hydrate Hazards
Methane hydrates are sensitive sediments. They can rapidly dissociate with an increase in temperature or a decrease in pressure. This dissociation produces free methane and water. The conversion of a solid sediment into liquids and gases will create a loss of support and shear strength. These can cause submarine slumping, landslides, or subsidence that can damage production equipment and pipelines. 
Methane is a powerful greenhouse gas. Warmer Arctic temperatures could result in gradual melting of gas hydrates below permafrost. Warming oceans could cause gradual melting of gas hydrates near the sediment-water interface. Although many news reports have presented this as a potential catastrophe, USGS research has determined that gas hydrates are currently contributing to total atmospheric methane and that a catastrophic melting of unstable hydrate deposits is unlikely to send large amounts of methane into the atmosphere. 
|Did You Know? Methane hydrate has a very high concentration of methane. If you melt a one cubic meter block of methane hydrate, about 160 cubic meters of gaseous methane will be released.|
|Methane Hydrate References|
 USGS Gas Hydrates Lab: Stephen Wessells, Laura Stern, Steve Kirby; United States Geological Survey Multimedia Gallery Video, 2012.
 A Global Inventory of Natural Gas Hydrate Occurrence: Keith A. Kvenvolden and Thomas D. Lorenson, Pacific Coastal & Marine Science Center, United States Geological Survey.
 Natural Gas Hydrates: A Review: Timothy S. Collett, Arthur H. Johnson, Camelia C. Knapp, Ray Boswell; Natural gas hydrates--Energy resource potential and associated geologic hazards: AAPG Memoir 89, p. 146-219, 2009.
 Gas Hydrates Offshore Southeastern United States: Carolyn Ruppel, Georgia Institute of Technology, NOAA Ocean Explorer website, last accessed November 2016.
 Assessment of Gas Hydrate Resources on the North Slope, Alaska, 2008: United States Geological Survey, Fact Sheet 2008-3073, October 2008.
 U.S. and Japan Complete Successful Field Trial of Methane Hydrate Production Technologies: United States Department of Energy press release, May 2, 2012.
 Energy Resource Potential of Methane Hydrate: An introduction to the science and energy potential of a unique resource; publication by the National Energy Technology Laboratory, United States Department of Energy, February 2011.
 Pure phase thermal property results: sI Methane Hydrate: Woods Hole Science Center, United States Geological Survey, 2007.
 Gas Hydrates and Climate Warming - Why a Methane Catastrophe Is Unlikely: Carolyn Ruppel and Diane Noserale, United States Geological Survey, Sound Waves Newsletter, May/June 2012.
 Study suggests large methane reservoirs beneath Antarctic ice sheet: Tim Stephens, press release, University of California Santa Cruz, August 29, 2012.
Although methane hydrate accumulations are located in difficult environments and present numerous technical challenges, they are widely distributed and the largest source of hydrocarbons on Earth. A variety of technologies could be developed to produce them using pressure reduction, ion exchange, and other processes that take advantage of their unique chemical and physical properties. The United States, Canada, Japan, and India all have vigorous research programs working to discover viable technologies for producing gas hydrates. Methane hydrate will likely play an important role in our future energy mix.
Contributor: Hobart King
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