Massive energy source may be deeply buried along the world's coastlines

March 28, 2001

About a mile offshore from the mouth of Northern California's Eel River, a steady stream of bubbles rises to the ocean's surface. For the longest time, no one knew why.

Now, scientists believe the once mysterious bubbles may be a telltale sign of an enormous new energy supply that could be extracted from offshore coastal areas.

The bubbles are methane, a common organic gas better known as natural gas. Millions of Americans burn natural gas in their home furnaces and stove burners, and it fuels hundreds of electricity generating power plants.

Only since the late 1970s have scientists understood that vast quantities of this basic gas lie beneath the sea along continental coasts -- trapped in ice crystals called methane hydrates.

Before the late 1970s, these crystals were known mostly to operators of natural gas pipelines in cold climates. At certain temperatures and gas line pressures, a hard, white, ice-like material would form inside these pipes, slowing or stopping the flow of natural gas. When pressure on these lines was relieved, or heat applied, the material would dissolve.

"We didn't know or have any reason to believe there were any natural gas hydrates on Earth," said Charles Paull, senior scientist and geologist for the Monterey Bay Aquarium Research Institute.

"We knew (only that) they could be made in chemical experiments, and formed in cold natural gas pipelines."

One clue that methane hydrates might exist in nature came from seismic profiles of the ocean floor. In some areas, these profiles revealed odd, undefined layers of material under the sea floor.

Another clue was that offshore drilling sometimes brought up blocks of material resembling dense, cloudy ice that fizzled and disappeared when brought to the surface.

Drilling offshore of North and South Carolina provided more definitive clues.

"The drilling program illustrated that gas hydrates were present in significant quantities in some areas, and made it clear that serious research was merited to assess how much of a methane hydrate resource was out there," said Paull, who participated in the federally sponsored project as a professor at the University of North Carolina at Chapel Hill.

Burning iceA chunk of methane hydrate is dense and milky, yet it floats like ordinary water ice. Released at the ocean floor, methane hydrate rises, fizzing like an Alka Seltzer as it discharges its gaseous contents. Frozen methane hydrate reaching the surface can be ignited, hence the term "the ice that burns."

Methane hydrate beds whet the appetite of energy experts for one important reason: One cubic meter of hydrate when dissolved will produce 165 to 180 cubic meters of methane. This is roughly the amount of natural gas an average California family burns for heating and cooking every month.

"It is clean energy, unlike coal or oil," said Miriam Kastner, geologist at UCSD's Scripps Institution of Oceanography who has investigated the Eel River resource.

Methane hydrates occur in patches along the coastlines of most continents. The total deposit may exceed 700,000 trillion cubic feet, or about twice the energy contained in all known fossil fuel resources worldwide, Kastner said.

Mapping by the U.S. Geological Survey indicates that methane hydrate deposits off the coast of the Carolinas are about 70 times greater than the amount of natural gas consumed by the United States in 1989.

So vast are the deposits under the sea floor that more fresh water is believed to be tied up within them than exists in all the world's rivers. Each cubic meter of methane hydrate also contains about 0.8 cubic meter of fresh water.

"Potentially there is a lot of energy there," Kastner said. "The problem is how is the gas distributed and how do you tell whether it is concentrated in a particular area or not."

Large resources are thought to be buried off the coasts of Northern California, Oregon, Washington and Alaska, as well as in the Gulf of Mexico, she said.

"There should also be methane hydrate in the Santa Barbara Channel, but this hasn't been proven," Kastner said.

How to do it

Finding and extracting methane from hydrate formations appear to be within -- or nearly within -- current engineering capabilities. Hydrate crystals are most stable under cold conditions. At 86 degrees, for example, the crystals must be kept under nearly 15,000 psi (pounds per square inch) of pressure to keep them from decomposing. But at 32 degrees, the pressure requirement is just 442 psi.

Some deposits of methane hydrate, layered with seafloor sediments, are believed to be 3,000 feet thick, but these veins exist at depths of 10,000 feet beneath the sea.

Experimental drilling programs have achieved this depth, but Paull said methane hydrate mining is more likely to begin in Arctic areas such as Alaska's North Slope, where persistent cold temperatures allow hydrates to exist at shallower ocean depths.

Even in the Arctic, though, questions remain about whether methane hydrate resources can be exploited as a major new source of energy.

"We don't know," said Paull. "There may not be many places where (methane hydrate resources) can be extracted in an economical way. But there probably are some sweet spots out there."

One challenge with Alaskan sources of methane is that there is no pipeline to transport the gas to marine terminals in the south. The existing pipeline carries only liquid oil.

But Paull said pressurized natural gas from hydrate fields could be piped into existing or future Alaskan oil wells, thus coaxing more oil from underground formations. "You might get another 20 percent out of an oil field this way," he said.

From ancient life

The methane locked up in hydrate crystals was created over the eons by the slow microbial decomposition of marine life. Marine organisms tend to concentrate along coastlines where cold water from the ocean depths rises, bringing nutrients to the surface.

Even in tropical and subtropical latitudes, methane hydrates form at depths of about 1,700 feet with average water temperatures of 42 degrees, Kastner said. Nations such as India and Japan, without natural domestic energy resources, are investing much more heavily in methane hydrate research than the United States, she said. (Currently, the Congressional budget allocates $9.96 million for methane hydrate research in 2001.)

The best way to find hydrate deposits may be with sonar. Hydrate layers are denser than other ocean sediments and show up as distinct sediments when the echoes are converted into cross-sectional printouts.

"With seismic reflections, we can see where the boundaries of these formations are, and we can calculate from physical chemistry where the boundaries should be, because we know the thermal gradients," Kastner said.

"Finding the hydrates will be very easy. The question is whether you will find them concentrated or disseminated."

A concentrated layer might be profitably mined. A loose layer of hydrates mingled with other matter might not be.

Another way to locate thick, solid hydrate veins is to look for the kind of gas emissions that rise from the sea floor near the Eel River, Kastner said.

In some cases, these gas bubbles also are signs of earthquake faults that allow warmer water or materials to come into contact with hydrate deposits. When such a fault runs through a methane hydrate layer, heat escaping from beneath the ocean floor dissolves some of the hydrate crystals, releasing methane to the surface.

Mining such deposits may involve significant environmental costs. As these hydrate layers give up their methane, they could crack and rupture, allowing crude oil underneath to seep to the surface and coat nearby beaches. Offshore landslides also could result, with undetermined implications for coastal communities.

Destruction of these layers, through ocean warming or earthquakes, may account for many of the large undersea landslides that have left geological scars offshore throughout history and pre-history, Paull said.

Ocean life also could be vulnerable. Rapid escape of methane from methane hydrate formations might eradicate large patches of ocean life by creating blooms of bacterial life that strip oxygen from sea water as they consume the methane.

Yet another consideration is that time may be running out to mine this potential resource. Some scientists believe global warming over the next few decades will cause shallower veins of gas hydrates to begin fizzing their methane into the atmosphere. But more methane may not be a good tonic for Earth.

A greenhouse gas, methane is at least 10 times more effective than carbon dioxide at retaining the Earth's heat.