METHANE HYDRATE: AN ENERGY SOURCE
SK ANSARI, SEEMA ANSARI
Oct 11 - 17, 2010
Methane hydrate is now getting serious attention of the players of energy sector world over. The strange crystal called methane hydrate comprising molecules of methane (the main component of natural gas) is trapped inside tiny cages of ice. This energy source occurs in huge quantity under ocean at a low temperature and a very high pressure. It is fossil fuel having ecological implications by emitting carbon dioxide in the atmosphere. However, technology is already in hand that can strip the carbon out of methane and produce hydrogen, which burns without releasing any carbon dioxide at all.
First observed in the 1800s, methane hydrate was initially regarded mainly as a nuisance formed in cold natural-gas pipelines. In 1964, however, a Siberian gas rig discovered a large methane hydrate deposit underground, spurring research on whether such deposits could be a good source of natural gas. Deep-sea exploration turned up even greater deposits in the oceans.
How much methane is locked in hydrates is uncertain, but underwater reserves are estimated at 35 to 177 quadrillion cubic feet. Notably, proven world natural gas reserves stand at only six quadrillion cubic feet.
There is a serious concern about extracting methane for world's use. Few people think that messing with the hydrates via mining is asking for trouble in the form of tsunamis, sea floor subsidence, and damage to underwater cables. When methane hydrate is mixed with sediment on the ocean floor, it prevents the sediment from solidifying properly and leads to instability. Undersea slides are dangerous for two reasons: they can release methane into the atmosphere, and they can cause tsunamis.
Presence of methane gas in coal seams has been known since the very beginning of the coal researches. However, its presence in ocean bottom sediments as 'hydrate' is a relatively recent discovery. Mysterious disappearance of ships, sudden plane crashes and many strange events on land have unfolded the mystery of 'Bermuda Triangle' in Atlantic Ocean. The Bermuda Triangle, earlier considered as the area of supernatural power, is now known as a powerful source of energy with huge accumulation of methane gas in the form of hydrate.
According to United States Geological Survey, two very small areas of north and south Carolina coast lying in a part of Bermuda Triangle contain gas equivalent to about 70 times the annual gas consumption of USA. The encouraging findings point towards high potentiality of methane hydrate as an alternative source of energy. Energy density of methane in hydrate is about 10 times greater than the non-conventional sources of gas and 2-5 times greater than that of conventional natural gas.
Gas hydrates are the ice-like compounds or solids formed by physical combination of a natural gas (mainly methane) and water, under specific conditions, in which water crystallises in the isometric crystallographic system rather than the hexagonal system of normal ice. All gases except hydrogen, helium, and neon form gas hydrates. Extreme cold (less than 7∞ C) and high pressure (greater than 50 atmospheres) are the prerequisites for hydrate formation.
Samples of methane hydrate are tough to acquire, requiring expensive drilling and elaborate schemes for core recovery and preservation. Previously developed methods for synthesising the stuff in the laboratory generally resulted in an impure material still containing some water that had not reacted with the methane.
A team is looking at the strength of gas hydrate samples in various temperature and pressure scenarios. Thus far, the team has found that water ice and methane hydrate have about the same strength at very low temperatures of 180 K and below. But, the hydrate is much stronger than ice at temperatures of 240 K and above. The most recent data indicate that methane hydrate is several times stronger than ice. Although methane hydrate is not as strong as rock, the data may be good news for the stability of the deposits.
Methane hydrates can be found offshore along most continents in the world and in some permafrost regions, such as Canada and Russia, where specific temperatures and pressures exist. In Canada alone, there are an estimated 500 trillion cubic meters of methane hydrate located mainly in the Beaufort-Mackenzie region above the Arctic Circle. This field contains one of the highest concentrations of natural gas hydrates in the world, and studies indicate that significant gas recovery is possible. Methane hydrates are also found offshore from Japan, where there is an estimated 14-year supply.
A lot of deposit is accumulating under the bed of ocean. Internationally coordinated researches are needed to harvest methane in a safe and cost effective manner considering environmental impact of mining and using methane hydrates.