In 1995,
the U.S. Geological Survey (USGS) made the first systematic assessment of the
in-place natural gas hydrate resources in the United States. That study suggested
that the amount of gas in the nation’s hydrate accumulations greatly exceeds
the volume of known conventional domestic gas resources. With higher natural
gas prices and forecasts of tight supply, new projects are pushing forward to
better understand the geologic, engineering and economic factors controlling
the ultimate energy resource potential of gas hydrates. However, gas hydrates
still present both scientific and technological challenges in turning them from
nonproducible accumulations of gas to a useable resource.
Resource potential
Research coring and seismic programs carried out by the Ocean Drilling Program,
government agencies and several industry consortia have significantly improved
our understanding of how gas hydrates occur in nature and have verified the
existence of highly concentrated gas hydrate accumulations at several locations.
Hydrates are found widely dispersed in permafrost regions and beneath the sea
in sediments of outer continental margins (see sidebar).
At the Mallik site in Canada’s Mackenzie
Delta, researchers undertook the first modern, fully integrated field study
to test the production potential of natural gas hydrates — an ice-like
solid mixture of methane gas and water located beneath the permafrost, which
some say could represent a new energy source. Image courtesy of the Mallik 2002
Project.
The estimated amount of natural gas contained in the world’s gas hydrate
accumulations is enormous, but is speculative and ranges over three orders of
magnitude, from about 2,800 to 8,000,000 trillion cubic meters of gas. Alexei
Milkov recently reported in Geology that the volume of gas trapped globally
in gas hydrate accumulations is in the range of 3,000 to 5,000 trillion cubic
meters of gas, which is four to seven times less than some of the more widely
cited estimates (see sidebar). By comparison, conventional
natural gas accumulations (reserves and technically recoverable undiscovered
resources) for the world are estimated at approximately 440 trillion cubic meters,
as reported in the U.S. Geological Survey World Petroleum Assessment 2000.
Despite the enormous range in reported gas hydrate volumetric estimates, even
the lowest estimates seem to indicate that gas hydrates are a much greater resource
of natural gas than conventional accumulations. It is important to note, however,
that none of these assessments have predicted how much gas could actually be
produced from the world’s gas hydrate accumulations. Much more work is
needed to go beyond these in-place gas hydrate volumetric estimates to assess
the hydrates as an energy resource.
Extraction
Gas recovery from hydrates is challenging because the gas is in a solid form,
and because hydrates are widely dispersed in hostile Arctic and deep marine
environments. Similar to conventional hydrocarbon production, the first recovery
of hydrate resources will occur in areas with the greatest concentration. Proposed
methods of gas recovery from hydrates generally deal with disassociating or
“melting” in-situ gas hydrates, by heating the reservoir beyond the
temperature of hydrate formation or decreasing the reservoir pressure below
hydrate equilibrium. Depressurization is considered to be the most economically
promising method for the production of natural gas from gas hydrates.
The Messoyakha gas field in northern Russia is commonly used as an example of
a hydrocarbon accumulation from which gas has been produced from hydrates by
simple reservoir depressurization. The field was developed for conventional
gas, and scientists have long thought that the sustained gas production was
due to the contribution of gas from gas hydrate into an underlying free-gas
accumulation. The production history of the Messoyakha field possibly demonstrates
that gas hydrates are an immediately producible source of natural gas and that
production can be started and maintained by “conventional” methods.
Developing the unconventional
The pace of projects to assess gas hydrate energy potential has accelerated
over the past several years because of the realization that this unconventional
resource could be developed in conjunction with conventional gas fields. The
most significant development was gas hydrate production testing conducted at
the Mallik site in Canada’s Mackenzie Delta in 2002.
The Mallik International Consortium is an international team, involving Japan,
Canada, the United States, India and Germany, as well as the International Continental
Scientific Drilling Program. Last December, the partners in the Mallik 2002
Gas Hydrate Production Research Well Program publicly released the results of
the first modern, fully integrated field study and production test of a natural
gas hydrate accumulation — allowing for the rational assessment of the
production response of a gas hydrate accumulation. Computer production simulations
supported by the project, including those performed by Lawrence Berkeley National
Laboratory, have shown that under certain geologic conditions, gas can be produced
from gas hydrates at very high rates, exceeding several million cubic feet of
gas per day.
Extraordinary technological developments in the petroleum industry — 3-D
seismic techniques, secondary recovery methods and horizontal drilling, for
example — have allowed the extraction of resources once thought to be unavailable.
Researchers often compare hydrates to coalbed gas resources, which were also
considered to be an unconventional and uneconomic resource in the not-too-distant
past. However, once geologists understood the resource, defined the reservoir
properties and addressed the production challenges, coalbed gas became an important
part of the nation’s energy mix. Now, coalbed gas is a viable fuel in its
own right and accounts for almost 10 percent of the natural gas production in
this country. Natural gas hydrates also may become economically extractable.
Global efforts
Past experience with the development of other unconventional energy resources
clearly shows that the evolution of gas hydrate into a producible source of
energy will require a significant and sustained research and development effort.
That effort has begun in the United States with the Methane Hydrate Research
and Development Act of 2000, which authorizes the expenditure of $43 million
over five years and directs the U.S. Department of Energy (DOE), in consultation
with USGS, the Minerals Management Service, the National Science Foundation,
the Department of Defense and the Department of Commerce, to commence basic
and applied research to identify, explore, assess and develop methane hydrates
as a source of energy.
Onshore Alaska and the offshore Gulf of Mexico are proven exploration targets
for gas hydrates (see sidebar). There, critical drilling
and transportation infrastructure exists that will allow gas hydrate prospects
to be drilled and produced from existing installations. In the Gulf of Mexico,
industry has begun characterizing hydrates on their oil and gas leases. And
industry-government partnerships are expected to drill hydrate prospects on
the North Slope of Alaska in the near future. Hence, the first domestic production
of hydrates may occur in Alaska, where gas from onshore hydrates will either
support local oil and gas field operations, or be available for commercial sale,
if and when a gas pipeline is constructed.
Many countries other than the United States are also interested in the energy
resource potential of gas hydrates. Japan, Canada, India and others have established
large gas hydrate research and development projects, while China, Korea, Norway,
Mexico and others are investigating the viability of forming government-sponsored
gas hydrate research projects.
In 1995, the government of Japan established the first large-scale national
gas hydrate research program, which now plays a leading role in worldwide gas
hydrate research efforts. Plans for 2004 included drilling and coring between
10 and 20 wells in the Nankai Trough off Japan’s east coast, where gas
hydrates were recovered during previous field studies in 2000. Japan has budgeted
more than $65 million (US) for this year’s gas hydrate studies.
India’s government is also funding a large national gas hydrate program
to meet its growing gas requirements. Seismic data have been acquired on the
Indian continental margin, and current plans call for drilling and coring dedicated
gas hydrate wells in 2005. In addition, gas hydrates were recently discovered
during drilling for conventional oil and gas resources in the Krishna-Godavari
Basin along the eastern coast of India.
Despite all the projects and timelines, however, the actual timing for expected
commercial production of hydrates remains uncertain. DOE has estimated that
gas production from gas hydrates could begin around 2015. In September 2003,
the National Petroleum Council reported that we are not likely to see significant
production from gas hydrates until sometime beyond 2025. However, initial production
from gas hydrates will most likely occur much sooner, especially in areas such
as the North Slope of Alaska and Canada. While estimates vary on when (and if)
gas hydrate production will play a significant role in the total world energy
mix, it is possible that hydrates will be able to provide a sustainable supply
of gas for the world’s future energy needs.
Although individual gas hydrate researchers often focus on issues ranging from
gas hydrates as a potential energy resource to a potential geologic hazard,
or as a possible agent of global climate change, all of these efforts are fundamentally
linked under our need to understand the geologic controls on these accumulations
in nature.
|
U.S.
projects under way TC |
Collett, T.S., 1993, Natural gas hydrates of the Prudhoe Bay and Kuparuk River area, North Slope, Alaska: American Association of Petroleum Geologist Bulletin, v. 77, no. 5, p. 793-812.
Collett, T.S., 1995, Gas hydrate resources of the United States, in Gautier, D.L., et al., eds., 1995 National assessment of United States oil and gas resources on CD-ROM: U.S. Geological Survey Digital Data Series 30.
Collett, T.S., 2002, Energy resource potential of natural gas hydrates: American Association of Petroleum Geologists Bulletin, v. 86, no. 11, p. 1971-1992.
Milkov, A.V., Claypool, G.E., Lee, Y-J., Xu, W., Dickens, G.R., Borowski, W.S., and the Ocean Drilling Program Leg 204 Scientific Party, 2003, In situ methane concentrations at Hydrate Ridge, offshore Oregon: New constraints on the global gas hydrate inventory from active margins: Geology, v. 31, no. 10, p. 833-836.
Back to top |
Geotimes Home | AGI Home | Information Services | Geoscience Education | Public Policy | Programs | Publications | Careers  |
Under the
Methane Hydrate Research and Development Act of 2000, the U.S. Department
of Energy (DOE) funds laboratory and field research on both Arctic and
marine gas hydrates. Among its current Arctic studies is a three-year
program sponsored by Maurer Technology and Anadarko Petroleum Corporation.
Anadarko spudded the Hot Ice 1 well on the North Slope of Alaska in March
2003 and completed it last February. Hot Ice 1 was designed to validate
geological, geophysical and geochemical models of onshore Arctic gas hydrate
occurrences.