Tuesday, December 19, 2006
Methane Hydrates: the next great energy source?
Methane hydrates, research has proven, are common in nature, in Arctic regions (most commonly in permafrost) and in marine sediments. Methane hydrates are crystaline solids that look very much like ice where gas molecules have been trapped in a cage of water molecules in the form of ice. The big difference is, this ice burns if exposed to a flame and will continue to support that flame on its own. Methane hydrates occur in stable ocean floor sediments resembling concrete below 300 meters down to about 500 meters (the Gas Hydrate Stability Zone or GHSZ). Above and below that zone hydrates to not form effectively as geothermal temperatures are too high for them to stabilize. That stability, however, is dependent on two primary factors, one being pressure and the other being temperature. It is believed that relatively small drops in ocean depth during the ice ages sufficiently reduces the pressure above methane hydrate deposits that the formations destabilize and release large volumes of trapped methane. Large scale sediment scarring in methane hydrate zones on the slopes of the continental shelf suggest frequent methane releases over the years as a contributing factor in underwater landslides. There is also a growing belief that large methane releases may be responsible for unexplained ship sinkings in areas like the Bermuda Triangle and the Devil's Triangle south of
Japan. These factors and the potential instability of the methane hydrates raises concerns about exploiting them as an energy resource with the potential of "losing" platforms in sudden methane releases. In addition, methane hydrates generally become unstable at temperatures above 18C even at pressure. At sea level they become unstable at even lower temperatures, possibly as low as 2C.
There has been considerable excitement and interest in methane hydrates as an energy and fuel source since the 1970s. Some have estimated that there is as much gas in the form of methane hydrates equivalent to twice the amount of all fossil fuel reserves on earth, or more. Estmiates over the last few decades, however, have steadilly declined by magnitudes. Where once methane hydrates were assumed to underly all the world's ocean bottoms it is now understood that they occur only in limited zones generally on continental shelves. It was also erroneously believed that because of the crystaline structure of the formations the gas would be concentrated much more densely than in conventional gas deposits. It is now believed that, in fact, the concentrations of methane hydrates in any area is generally much lower than originally estimated. In fact in most sites it is believed that the hydrates are too dispersed for economic extraction.
One of the serious problems about methane hydrates is that methane is more than ten times as effective as a greenhouse gas than is carbon dioxide. The suspected positive feedback processes that occur with global warming can cause massive releases of sequestered methane which then further increases atmospheric temperatures which causes further releases of methane in a viscious spiral that can end in a rapid onset of a new ice age. This is, in fact, one of the primary concerns with the increase in ocean temperatures, particularly in cold polar oceans that host large concentrations of methane hydrates, that is occuring in the current phase of global warming. Since it is believed that the earth contains 3,000 times the methane in hydrate form than is currently in the atmosphere the risk involved in initiating a large-scale destabilization and release of these gases is very worrying. More visible and equally concerning is the ongoing release of methane from hydrates in Arctic permafrost that is resulting from global warming. Temperature increases from global warming are, in fact, greater in the polar regions than in equatorial and temperate regions. The potential of a positive feedback mechanism in these polar regions due to permafrost methane releases is very high as is the risk of destabilizing global climate.
Energy companies, despite frequent and ubiquitous press releases to the contrary, do not have a good track record of concern for the impact of their operations on the environment. The risk of very large releases of potent greenhouse gasses while attempting to exploit these methane hydrate deposits is sufficiently high that we should demand a full long-term understanding of the nature and characteristics of these deposits before any consideration of granting exploration and development licenses. The concern is, with declining economically viable natural gas reserves, that the "need" for energy will preclude environmental concerns. Thus far there appears to be no imminent rush to exploit these reserves. Seemingly careful testing is being conducted both in the arctic and in select oceanic reserves. Once we go into rapid natural gas decline, however, coupled with an increasing North American social infrastructure dependent on gas, will such care continue to be taken? Or will we yet again compromise on environmental protection for the sake of satisfying our growing energy lust? Only time will tell.