Through the steady, silent industry of countless bacteria digesting the ocean's organic debris, a surprising stash of methane gas has been deposited beneath the sea—trapped in ice like crystals in floor sediments.
To the eye, the deposits may look like nodules or veins of ice glistening on the murky ocean bottom. But this odd quarry, discovered only two decades ago, is now the object of a great geological quest, for some scientists think the microscopic methane molecules locked inside could eventually provide salvation for energy-hungry societies around the globe.
These methane deposits may hold twice as much carbon as all the other fossil fuels on earth—coal, oil, and existing sources of natural gas—combined, Thus, this reservoir may represent huge energy sources for the future.
The so-called methane hydrates form when the methane gas—excreted by sea bacteria that primarily consume phytoplankton as well as the flesh of assorted dead organisms—dissolves and forms into crystals in the icy cold waters and tremendous pressures at the bottom of the sea. This process, which has probably continued for millions of years, has left huge deposits of the natural gas.
In fact, one pocket alone, about 54 km by 180 km area called the Blake Ridge off the North Carolina coast, holds enough gas to supply all the needs of the United States for 100 years estimates a US Geological service expert..
Chemists first mused in the 1930s about the possible existence of an odd state of matter in which high pressure could cause water to crystallize around a gas. But they dismissed that prescient thought as nothing more than a fanciful theoretical exercise.
Then in the spring of 1970 during a scientific expedition to study the sea floor, ocean geologists were puzzled by the bizarre, fizzing icy sedimentary cores they retrieved. This “thing” constantly bubbled and bubbled for hours.
Other researchers noticed a correlation between the site of the fizzing core and anomalies on sonar maps of the ocean floor that had been made to study sea-floor geology and tectonics. The sound waves, which travel at different speeds through different materials, accelerated as they passed through the icy deposits within the surrounding denser sedimentary rock.
Using sonar to locate more such deposits, researchers have found massive concentrations along the East Coast of the United States, typically in the relatively shallow waters of the continental shelf.
Hydrates have also been discovered off the coasts of California, Washington, and Alaska. In fact, the coastal waters of the north slope of Alaska alone hold an estimated 44 trillion tons of methane hydrates—more than a two-year supply for the United States' needs. Since deposits have usually been discovered serendipitously during ocean floor-mapping expeditions, scientists believe many other hydrates surely must exist.
In a major step toward one day realizing this potential energy bounty, a 16-nation team of scientists will sail down the Atlantic coast of North America in November and December to retrieve samples of the hydrates from the deep. The eight-week journey should help researchers interpret future sonar mapping data more accurately and yield better estimates about whether recovery efforts would be economical.
The researchers will drill a succession of holes in the sea floor and extend thin pipes through which they will lower equipment for sending sound waves through the rock and hydrate deposits. This will enable them to better assess hydrate deposit sizes, since the waves can be studied before they become distorted as they reflect back through the water to the surface. The sonar tests can then be correlated with surface sonar mapping to better interpret those images and analyze future sonar images.
The researchers will also use a special chamber that returns samples to the surface under the same intense pressures that exist on the ocean floor. The team will study the hydrates' molecular structure and look for clues about how the methane gas might be harvested. For instance, one approach is to melt the deposits so the gas can be vented to the surface.
Using traditional gas or oil drilling techniques, concentric pipes could be placed on the ocean bottom. Then warm water, perhaps surface waters, could circulate down through one pipe to melt the crystals, while the released gas could travel through the other pipe to the surface.
But such an approach would have to be refined, says Rodney Malone, a geologist at the U.S. Department of Energy and former manager of the agency's methane hydrate research program, which was ended in 1993 because administrators decided that hydrate use could be decades away. For example, questions remain about how easily the crystals would melt and whether the energy spent would be excessive for the amount of methane returned.
There is also a risk that the melting crystals might destabilize a region of the ocean floor, turning it into a slurry of mud that could damage the pipe rigging. Companies may also be reluctant to invest the many tens of millions of dollars required for such special drilling equipment, he adds. While most ocean oil rigs can drill to depths of several hundreds of meters, hydrate rigs must be able to reach deposits often found at depths of kilometer or more.
Other economic factors may also play a role in hydrate development. For now, abundant, untapped deposits of methane are accessible on land and in ocean rock. There is no immediate need to take the risk.
Even so, Japan is moving forward with methane hydrate research. Besides sending a team on the Atlantic coast expedition this fall, the Japanese government has planned a demonstration project of hydrate harvesting by 1999 in the Nankai Trough off the east coast of Japan's main island.
And in the United States, improved assessments of hydrate abundance and geological stability expected from the upcoming expedition could influence companies' willingness to fund further research and development. Moreover it can not longer ignore these deposits as curious phase transitions. In the future, the hunt for less easily accessible amounts of fossil fuels, will continue.
© 2000 Mena Report (www.menareport.com)
