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Last Updated: Jun 25, 2009 - 11:05:19 AM |
By the late 70s, they were on the brink of winding down the operation.
According to their surveys, they had sapped nearly all the methane from
the deposit. But despite their estimates, the gas just kept on coming.
The field continues to power Norilsk today.
Where is this methane coming from? The Soviet geologists initially
thought it was leaking from another deposit hidden beneath the first.
But their experiments revealed the opposite - the mystery methane is
seeping into the well from the icy permafrost above.
If unintentionally, what they had achieved was the first, and so far
only, successful exploitation of methane clathrate. Made of molecules
of methane trapped within ice crystals, this stuff looks like dirty ice
and has the consistency of sorbet. Touch it with a lit match, though,
and it bursts into flames.
Clathrates are rapidly gaining favour as an answer to the energy
crisis. Burning methane emits only half as much carbon dioxide as
burning coal, and many countries are seeing clathrates as a quick and
easy way of reducing carbon emissions. Others question whether that is
wise, and are worried that extracting clathrates at all could have
unforeseen and perilous side effects.
If countries and companies are exploring the potential of clathrates
only now, that's not for lack of scientific interest over the years.
Research over the past two decades has shown that the energy trapped in
ice within the permafrost and under the sea rivals that in all oil,
coal and conventional gas fields, and could power the world for
centuries to come. Oil and gas companies have been slow to catch on,
however, believing methane clathrates to be unreliable and
uneconomical. Feasibility studies and the diminishing supplies of
conventional natural gas are changing that, making commercially viable
production realistic within a decade, says Ray Boswell, who heads the
clathrates programme at the US Department of Energy.
"Just a few years ago no one was thinking about clathrates as an energy
source," Boswell says. "Now there is a great deal of interest in them."
It is not just the US. Canada, China and Norway are entering the race
too. The governments of Japan and South Korea have given the green
light for full-scale production. The first intentional commercial
exploitation may come as early as 2015.
So what are methane clathrates, and where do they come from? As with
all natural gas, the story starts with rotting plants. As these plants
decay, they release methane, which permeates through porous rocks
underground. If the conditions where the methane ends up are just right
- temperatures close to 0 °C and pressures of roughly 50 atmospheres -
ice crystals form that trap the gas in place.
In practice, these conditions mostly occur within and underneath
permafrost and beneath the seabed on continental shelves, usually at
ocean depths of 200 to 400 metres, although clathrates have also been
known to appear on the seabed. In 2000, a 1-tonne chunk of the stuff
was scooped up by fishermen off Vancouver Island in British Columbia.
They hastily dumped the hissing mass back into the ocean.
Until recently, these deposits escaped the serious attention of energy
companies. Engineers stumbled on clathrates from time to time while
drilling for conventional reserves of oil and gas, but they were mostly
viewed as an irritant that caused blowouts or blocked pipelines.
That view changed with studies showing that the gas is often present at
a given site in concentrations of 50 per cent or more in ice's pore
space - values similar to the prevalence of natural gas in traditional
sources - in layers of clathrate hundreds of metres thick. What's more,
in its constricted surroundings the gas is compressed to 160 times its
density at atmospheric temperature and pressure, making for vast
quantities of it when released.
These revelations made clathrates a potential gold mine that countries
and energy companies are now eagerly prospecting. In 2007, a US project
found clathrate reserves in Alaska with 80 per cent of the ice's pore
space packed with methane. Tim Collett, a clathrate specialist at the
US Geological Survey who was part of the team, says there may be
reserves all along the Alaska north slope, including beneath existing
oil installations at Prudhoe Bay and, alarmingly for environmentalists,
the Arctic National Wildlife Refuge.
Collett estimates there is between 0.7 and 4.4 trillion cubic metres of
methane clathrate in Alaska alone. Even the low end of that range could
heat 100 million homes for a decade. "It's definitely a vast storehouse
of energy. But it is still unknown how much of the volume can actually
be produced on an industrial scale," he told a meeting of the American
Chemical Society at Salt Lake City, Utah in March this year.
That's not the only reserve of interest. In 2004, a German and Chinese
team found methane venting from the seabed off the coast of Taiwan in
the South China Sea, and in 2006 Indian researchers found a layer of
methane clathrates 130 metres thick off its east coast in an area known
as the Krishna-Godavari basin. Collett calls these "one of the world's
richest marine gas clathrate accumulations".
Estimates vary, but conservative figures place global reserves at
roughly 3 trillion tonnes of previously untapped carbon - more than is
trapped in all the other known fossil fuel reserves put together, says
Klaus Wallmann of the Leibniz Institute of Marine Science in Kiel,
Germany.
That would last about 1000 years if we continue to use natural gas at
the current rate, estimates Collett. Even if the methane from
clathrates replaced all fossil fuels, and not just gas, it would still
last for at least 100 years. But with this methane held in fragile ice
crystals and buried deep within the Earth, can it be exploited safely
and economically?
Until recently, there were two methods of extracting methane from
clathrates that were considered feasible. One is to drill a hole into
the clathrate deposit to release the pressure, allowing the methane to
separate out from the clathrate and flow up the wellhead. The second is
to warm the clathrate by pumping in steam or hot water, again releasing
the methane from its icy matrix.
In 2002, Canadian, American, Japanese, Indian and German researchers
tested both techniques in the field, at a drill site called Mallik on
the outer extremity of the Mackenzie river delta in the Canadian
Arctic. Both were successful, but the energy costs of the heating
method nearly outweighed the energy gained from the methane released,
making depressurisation the more attractive option.
The potential of depressurisation was confirmed in March 2008, when
Canadian engineers led by Scott Dallimore of the Geological Survey of
Canada used the technique to tap 20,000 cubic metres of methane gas
over six days from a deposit located 1 kilometre beneath Mallik.
Similarly, in 2007, South Korea exploited depressurisation to extract
methane clathrate from the Ulleung basin in the Sea of Japan. Officials
believe reserves there could meet the country's gas needs for up to 30
years, and they plan to begin production by 2015. Meanwhile Japan,
another country with limited fossil fuel reserves, has found up to 50
trillion cubic metres of clathrate south-east of Honshu Island in the
Nankai trough - enough to supply the country with natural gas for
centuries. In March 2008, the Japanese cabinet pledged to begin
production by 2016.
So methane clathrate extraction seems to be imminent, in Asia at least.
Whether it is desirable is another matter. Some argue that the world
shouldn't be tapping a new fossil fuel while we are pledging to build a
low-carbon economy. Methane might be less carbon intensive than fuels
such as coal, but switching to methane would not help countries to
reach ambitious targets for reducing carbon emissions of up to 80 per
cent by 2050.
To make matters worse, the methane itself could exacerbate global
warming if it starts leaking from the reserves. Methane is, molecule
for molecule, 20 times as powerful at warming the air as CO2. Rising
sea temperatures could melt some undersea clathrate reserves even
without extraction projects disturbing them, triggering a release of
this potent greenhouse gas. A decade ago, Peter Brewer of the Monterey
Bay Aquarium Research Institute in Moss Landing, California, showed how
clathrates on the seabed just off the coast of California disappeared
after an El Niño event raised ocean temperatures by 1 °C.
Exploitation of clathrate reserves might exacerbate this problem, but
it could also have far more immediate adverse effects. Clathrates exist
in a delicate balance, and the worry is that as gas is extracted its
pressure will break up neighbouring clathrate crystals. The result
could be an uncontrollable chain reaction - a "methane burp" that could
cascade through undersea reserves, triggering landslips and even
tsunamis. "Extraction increases the risk of large-scale collapses,
which might have catastrophic consequences," says Geir Erlsand from the
University of Bergen in Norway.
Disturbing the clathrates' delicate balance might unleash an
uncontrollable 'methane burp'
Evidence that such events have happened in the past comes from the
Storegga slide, a landslip on the seabed off western Norway about 8000
years ago. A 400-kilometre stretch of submarine cliff on the edge of
the continental shelf collapsed into the deep ocean, taking with it a
staggering 3500 cubic kilometres of sediment that spread across an area
the size of Scotland. The result would have been a tsunami comparable
to the one that devastated parts of south-east Asia in 2004.
The naval researchers who first discovered the remains of the slide in
1979 assumed it was the result of an earthquake. Perhaps it was
initially, but Jürgen Mienert of the University of Tromsø in Norway has
found that the slumped area was also a hotspot for methane clathrates.
The sheer number of cracks and giant pockmarks on the seabed,
carbon-dated to the time of the slide, suggest billions of tonnes of
methane must have burst out of the cliff along with the sediment, a
possible trigger for the landslip. The resulting explosions would have
turned even a minor slip into a major disaster.
Sinking carbon
The Storegga slide is not the only incident of this kind. The ocean
floor from Storegga to Svalbard is full of pockmarks that might have
been caused by similar clathrate-driven landslides, says Mienert. He
says we will see more of these events in the future. "Global warming
will cause more blowouts and more craters and more releases," he warns.
Other engineers believe claims that clathrate extraction poses a risk
are little more than scare stories with little supporting evidence.
Wallmann claims that the Chinese and Indians in particular are "afraid
that the west wants to prevent them from rapid extraction of methane
clathrate".
There might in fact be a safer way of tapping clathrates which, if
successful, could quash the criticisms. Since other gases can also form
clathrates, it should be possible to pump one of these gases into the
crystals to displace the methane. Carbon dioxide would be an ideal
candidate, says Ersland - the resulting crystal is even more stable
than methane clathrate, meaning another greenhouse gas would be stored
out of harm's way.
Ersland has already demonstrated his technique in the lab. In joint
research with the energy company ConocoPhillips based in Houston,
Texas, he replaced methane with CO2 in artificial clathrate crystals.
The exchange was rapid and did not damage the clathrate structure,
making it the safest way to extract the methane yet found (Chemical
Engineering Journal, DOI: 10.1016/j.cej.2008.12.028). Substituting
methane with CO2 "will increase the stability of the reservoir
sediments as well as maintaining the clathrates in their solid state",
Ersland says.
The acid test will be an experiment planned for January next year.
ConocoPhillips intends to pour liquefied CO2 down a borehole into the
Alaskan north slope's clathrate deposit. If all goes well, the CO2 will
fill the clathrate crystals and the displaced methane will shoot up the
wellhead to the surface. The method could be both a safe way of
capturing the methane and an environmental argument for pursuing the
goal - the clathrate structures would be acting as a carbon sink.
It is an intriguing possibility. Sooner rather than later, burning
fossil fuels like coal and natural gas will only be acceptable if the
CO2 emissions are captured and stored. Right now, there is a rush to
develop a practical system for capturing and burying billions of tonnes
of CO2 underground per year.
So far, the focus has been on old oil wells, salt deposits and even old
coal mines. The big problem is that the huge infrastructure required to
dispose of the CO2 may quickly make burning fossil fuels uneconomic
compared with alternatives like solar, wind or nuclear power. Disposing
of CO2 down the same pipe used to bring up more fuel could be the
answer.
Source:Ocnus.net 2009
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