The resource known as gas or methane hydrates,
which lies frozen in combustible ice crystals below the ocean floor
-- or closer to the surface in the Arctic regions -- has been estimated
to represent double the energy potential of all of the world's conventional
oil, gas and coal reserves combined.
That is a potential that has many geoscientists and
industry companies anxious about the future -- and with good reason.
But Timothy S. Collett, a research geologist for
the U.S. Geological Survey, Denver, who has been involved in the
research of gas hydrates for the past 20 years, sees the question
marks that accompany the potential.
Collett, who delivered a paper on the subject at
last year's AAPG Wallace C. Pratt Memorial Conference on Petroleum
Provinces in the 21st Century, believes that along with the vast
possibilities, there are considerable uncertainties.
For starters, Collett lists three main issues.
♦
There are hazards involved.
Typically, when a conventional drilling installation
is set up on the ocean floor that will drill through the hydrate
crystals, the gas can become separated from the water, causing an
explosion. Also, this separation can upset the solidity of the sediment
on the ocean floor, creating a landslide effect.
The latter is not a danger on Arctic land surfaces,
but the explosion danger is there.
♦ It
is not yet clear whether these methane gases can be harvested in
an environmentally safe way without contributing to the greenhouse
effect, or destabilizing continental margins, possibly triggering
undersea landslides and potentially cataclysmic tsunami waves.
Some experts point to evidence that massive, naturally
occurring releases of these gases in the past contributed to abrupt
changes in the earth's climate, as well as towering tsunami waves
like one that wreaked havoc in northern Europe 8,000 years ago.
♦
The harnessing of these gases as an energy resource is a difficult
proposition, although, in this issue, real progress has been made.
Collett said that since the 1970s the Ocean Drilling
Program (ODP) and its parent Deep Sea Drilling Program (DSDP) have
acquired a significant number of samples of direct geologic data
relating to these hydrates. These explorations have been scientific,
and dealt with issues such as plate movements and climate changes
regarding these hydrates.
"Basically, these hydrates have been revealed
to exist around the ocean margins of the world," Collett said.
"However, many occur within clay dominated rock sequences,
which would not be considered as a conventional reservoir."
Collett adds that there are often low concentrations
of this gas, though they are distributed over a broad area.
On the other hand, highly concentrated quantities
of this gas have been discovered within conventional reservoir routes
in the Arctic, specifically in the west Siberian basin of Russia,
the McKenzie River Delta in Canada and on the North Slope in Alaska.
Accidents and Intentional Lessons
In the late 1960s and early 1970s, Russians drilling
in the Messoyakha field in northeast Siberia discovered this gas
by accident.
The Russians were drilling for conventional gases,
which were underlain by the hydrate gases. The drilling changed
the pressure of the reservoir, releasing the underlying gases, producing
a bonanza that hadn't been anticipated.
It was only afterwards, in noting the changes in
the reservoir pressure, that the Russians concluded the existence
of the hydrate gases. The nature of the findings, however, was not
particularly helpful for future research.
A more intentional -- and more valuable -- effort
in terms of measurable results was made in 1998 by the Japanese
National Oil Corp. and Geological Survey of Canada in McKenzie,
in the Mallik 2L-38 gas hydrate research well.
The results of this venture (published in the 1999
Geological Survey of Canada Bulletin 544) confirmed both the existence
of the hydrates and the viability of the engineering technology
designed to harness the same.
Partnerships are now being formed for actual drilling
in 2002. The USGS and Department of Energy will be involved as secondary
partners, along with others. In fact, in 1993, Collett published
through the USGS an AAPG article reviewing the distribution of gas
hydrates around the Prudhoe Bay oil fields.
"From this study," Collett said, "I
concluded that the Prudhoe Bay field may contain as much as 45 trillion
feet of gas."
There When You Need It?
The driving force in these endeavors, however, is
the Japanese National Oil Corp., in partnership with its government.
Japan has been engaged in the Mallik venture mainly to learn what
it could for its more immediate project in the Nanakai Trough, just
off of the southeast coast of Japan.
The reason is clear.
"Japan imports 98 percent of its energy resources,"
Collett said, "so that country has the motivation to spend
much more time and money in making gas hydrates a viable source
of energy."
Collett adds that, in terms of gas hydrates, the
Mallik and Nanakai wells are geologically very similar.
The United States, however, doesn't face a similar
urgency, and Collett doesn't see the existing structure for energy
exploration being challenged soon.
"I don't believe there will be a rush to market
the gas hydrates," Collett said. "I don't think there
will be a significant offshore interest in marine gas hydrates for
30 or more years.
"However, in very localized areas, such as the
North Slope in Alaska, I believe there may be some real domestic
activity within the next 10 years or so."