B.C. methane hydrates
A two-year search
that culminated in August with the discovery of one of Canadas largest deposits
of methane hydrates began with a fisherman off the coast of British Columbia.
We were tipped off more or less accidentally by a fisherman who dragged
up a piece of hydrate in his net, says geophysicist Ross Chapman of the
Centre for Earth and Ocean Research at the University of Victoria, B.C., and the
principal investigator on the project. When it came up to the surface, it
would have behaved like a giant Alka Seltzer foaming and bubbling.
That frothy activity was the release of methane from its icy cage as it surfaced
from underwater, undergoing a change in pressure and temperature that destabilized
the structure of the ice lattice.
A methane hydrate glacier sits on the seafloor,
850 meters below the surface. Photo courtesy of University of Victoria, B.C.
Using a tiny underwater rover called ROPOS, with the support of Canadas
Natural Sciences and Engineering Research Council, the U.S. Naval Research Lab
and the Canadian Scientific Submersible Facility, Chapman and his colleagues followed
the track that the fisherman and his crew had traveled two years before. The rover
traveled on the seafloor, about 850 meters deep. Eventually we found a little
plateau, with a series of what you have to call hydrate glaciers, Chapman
says. Scattered over about 2 square kilometers, the glacier-like mounds were surrounded
by clam beds, although no vents were visible. One mound was the size of
a Volkswagen, he says.
Researchers estimate that this extensive field of hydrates at the bottom of submarine
Barkley Canyon off the British Columbia coast, could provide enough methane to
power Canada for four decades. But, they say it is too soon to tell exactly how
much is in Barkley Canyon.
From other evidence, Chapman believes that the ice may cap deeper deposits of
very clean oil. He noticed that the ice was a yellow brown, indicating that the
hydrocarbons were from a deeper source, where vigorous enough fluid flow
and some kind of vent to the seafloor created an escape route. When ROPOS
arm poked into the sediments, it released clear, light oil, presumably from that
deeper reservoir, he adds.
Ices like those found at Barkley Canyon are surprisingly common in deep near-shore
sedimentary deposits and at continental margins, as well as in permafrost. They
are usually stable at water depths below 300 to 500 meters and are at optimum
temperatures at the seafloor, about 4 degrees Celsius. Some methane hydrates are
made by methanogens, or bacteria that thrive on methane, but the B.C. deposits
may be completely thermogenic, derived from the same processes that cook
oil and gas, Chapman says.
Worldwide, methane hydrate sources are estimated to be equivalent to 137.5 trillion
barrels of oil. But its not that easy to take advantage of this cornucopia.
While methane hydrates could provide a very clean source of hydrocarbon fuel,
the methane, if released accidentally, is a greenhouse gas oxidizing to
carbon dioxide and remaining in the atmosphere for a long time. And because methane
hydrates are easily destabilized, Chapman points out that they may cause submarine
slumps, which represent an additional geohazard. Such massive releases may have
been responsible for extinctions at the end of the Paleocene, according to recent
British Columbia has had a moratorium, in place since the early 1970s, on coastal
oil and gas exploration to avoid environmental impacts. Nevertheless, Chapman
says the Barkley Canyon deposits provide a natural laboratory for studying hydrates.
We have a team thats looking at long-term experimental research on
this particular site, he says, and they plan to publish their summers
Geotimes contributing writer