CV
27th June 2006, 17:12
taken from the US Dept of Energy official site http://www.fossil.energy.gov/programs/oilgas/hydrates/index.html
A methane hydrate is a cage-like lattice of ice, inside of which are trapped molecules of methane (the chief constituent of natural gas). In fact, the name for its parent class of compounds, "clathrates," comes from the Latin word meaning "to enclose with bars."
Methane hydrate form in generally two types of geologic settings: (1) on land in permafrost regions where cold temperatures persist in shallow sediments, and (2) beneath the ocean floor at water depths greater than about 500 meters (about 1,640 feet) where high pressures dominate. The hydrate deposits themselves may be several hundred meters thick.
Scientists have known about methane hydrate for a century or more. French scientists studied hydrate in 1890. In the 1930s, as natural gas pipelines were extended into colder climates, engineers discovered that hydrate, rather than ice, would form in the lines, often plugging the flow of gas.
These crystals, although unmistakably a combination of both water and natural gas, would often form at temperatures well above the freezing point of ordinary ice. Yet, for the next three decades, methane hydrate was considered only a nuisance, or at best, a laboratory oddity.
That viewpoint changed in 1964. In a northern Siberian gas field named Messoyakha, a Russian drilling crew discovered natural gas in the "frozen state," or in other words, methane hydrate occurring naturally. Subsequent reports of potentially vast deposits of "solid" natural gas in the former Soviet Union intensified interest and sent geologists worldwide on a search for how -- and where else -- methane hydrate might occur in nature. In the 1970s, hydrate was found in ocean sediments.
In late 1981, the drilling vessel Glomar Challenger, assigned by the National Science Foundation to explore off the coast of Guatemala, unexpectedly bored into a methane hydrate deposit. Unlike previous drilling operations which had encountered evidence of hydrate, researchers onboard the Challenger were able to recover a sample intact.
Today, methane hydrate has been detected around most continental margins. Around the United States, large deposits have been identified and studied in Alaska, the west coast from California to Washington, the east coast, including the Blake Ridge offshore of the Carolinas, and in the Gulf of Mexico.
In 1995, the U.S. Geological Survey (USGS) completed its most detailed assessment of U.S. gas hydrate resources. The USGS study estimated the in-place gas resource within the gas hydrate of the United States ranges from 112,000 trillion cubic feet to 676,000 trillion cubic feet, with a mean value of 320,000 trillion cubic feet of gas. Subsequent refinements of the data in 1997 using information from the Ocean Drilling Program have suggested that the mean should be adjusted slightly downward, to around 200,000 trillion cubic feet -- still larger by several orders of magnitude than previously thought and dwarfing the estimated 1,400 trillion cubic feet of conventional recoverable gas resources and reserves in the United States.
Worldwide, estimates of the natural gas potential of methane hydrate approach 400 million trillion cubic feet -- a staggering figure compared to the 5,500 trillion cubic feet that make up the world's currently proven gas reserves.
A methane hydrate is a cage-like lattice of ice, inside of which are trapped molecules of methane (the chief constituent of natural gas). In fact, the name for its parent class of compounds, "clathrates," comes from the Latin word meaning "to enclose with bars."
Methane hydrate form in generally two types of geologic settings: (1) on land in permafrost regions where cold temperatures persist in shallow sediments, and (2) beneath the ocean floor at water depths greater than about 500 meters (about 1,640 feet) where high pressures dominate. The hydrate deposits themselves may be several hundred meters thick.
Scientists have known about methane hydrate for a century or more. French scientists studied hydrate in 1890. In the 1930s, as natural gas pipelines were extended into colder climates, engineers discovered that hydrate, rather than ice, would form in the lines, often plugging the flow of gas.
These crystals, although unmistakably a combination of both water and natural gas, would often form at temperatures well above the freezing point of ordinary ice. Yet, for the next three decades, methane hydrate was considered only a nuisance, or at best, a laboratory oddity.
That viewpoint changed in 1964. In a northern Siberian gas field named Messoyakha, a Russian drilling crew discovered natural gas in the "frozen state," or in other words, methane hydrate occurring naturally. Subsequent reports of potentially vast deposits of "solid" natural gas in the former Soviet Union intensified interest and sent geologists worldwide on a search for how -- and where else -- methane hydrate might occur in nature. In the 1970s, hydrate was found in ocean sediments.
In late 1981, the drilling vessel Glomar Challenger, assigned by the National Science Foundation to explore off the coast of Guatemala, unexpectedly bored into a methane hydrate deposit. Unlike previous drilling operations which had encountered evidence of hydrate, researchers onboard the Challenger were able to recover a sample intact.
Today, methane hydrate has been detected around most continental margins. Around the United States, large deposits have been identified and studied in Alaska, the west coast from California to Washington, the east coast, including the Blake Ridge offshore of the Carolinas, and in the Gulf of Mexico.
In 1995, the U.S. Geological Survey (USGS) completed its most detailed assessment of U.S. gas hydrate resources. The USGS study estimated the in-place gas resource within the gas hydrate of the United States ranges from 112,000 trillion cubic feet to 676,000 trillion cubic feet, with a mean value of 320,000 trillion cubic feet of gas. Subsequent refinements of the data in 1997 using information from the Ocean Drilling Program have suggested that the mean should be adjusted slightly downward, to around 200,000 trillion cubic feet -- still larger by several orders of magnitude than previously thought and dwarfing the estimated 1,400 trillion cubic feet of conventional recoverable gas resources and reserves in the United States.
Worldwide, estimates of the natural gas potential of methane hydrate approach 400 million trillion cubic feet -- a staggering figure compared to the 5,500 trillion cubic feet that make up the world's currently proven gas reserves.