By SUSAN EATON
Its technically challenging to drill through 640 meters of
permafrost and 110 meters of gas hydrates -- thermal and mechanical
erosion of the borehole can result from transferring heat into the
gas hydrates while drilling. Melting of the hydrates can cause slumping
or possible blowouts from dissociation of the gas, water and sediments.
Innovative drilling protocols, therefore, were developed for the
Mallik 2002 research project -- the mud was cooled to 2 °
Celsius, and the surface casing was insulated to reduce heat transfer
into the gas hydrate zone.
The open hole logging program for Mallik 5L-38 included nuclear
magnetic resonance, dipole sonic, and high resolution electrical
conductivity and resistivity tools. A continuous core was cut from
885 to 1,151 meters, through the highly concentrated, main gas hydrate
intervals and below a free gas interval. Downhole fibre optic temperature
sensors measured in situ formation temperatures, noting changes
during drilling and production tests.
Production testing at Mallik 5L-38 involved measuring gas and water
flows at surface in response to depressurizing the gas hydrate reservoir.
Five one-meter intervals were selected for pressure draw down experiments.
Additionally, a 13-meter thick zone was perforated, enabling warm
fluids to circulate into the gas hydrate reservoir for a period
of seven to nine days.
Small-scale fractures were induced into the reservoir to determine
the effects of fracturing on gas flow.
-- SUSAN EATON
The consortium that undertook the production testing
program at Mallik featured the participation of the International
Continental Scientific Drilling Program, and included:
The Geological Survey of Canada.
The Japan National Oil Corp.
U.S. Geological Survey.
U.S. Department of Energy.
India Ministry of Petroleum and Natural Gas.
Gas Authority of India.
A join venture consisting of Chevron Canada Resources-BP Canada
Energy-Burlington Resources Canada.
RETURN TO STORY
The recent discovery by geophysicists
from the University of Victoria of a spectacular gas hydrate glacier
outcropping on the sea floor of Canada's Pacific margin has focused
attention on this most unconventional energy resource.
There's a lot at stake: About 50 percent of Canada's
landmass is underlain by permafrost, and trapped below the terrestrial
permafrost layers are massive volumes of gas hydrates locked
in sedimentary rocks that may contain enough energy to dwarf
Canada's conventional gas reserves.
The key to establishing gas hydrates as a significant
energy resource for Canada, however, is whether the methane gas
that is frozen within a lattice of water molecules can ever be produced
economically and safely.
the winter of 2002, working in subzero temperatures and under cover
of darkness in the Canadian Arctic, an international
consortium led by the Natural Resources Canada's Geological
Survey of Canada (GSC) and the Japan National Oil Corp. spent C$25
million to evaluate gas hydrates as a potential energy source. Gas
flares from the world's first production tests of gas hydrates lit
up the Arctic sky at the Mallik 5L-38 well, situated on Richards
Island in the Mackenzie Delta and adjacent to the Beaufort Sea.
Mallik represents one of the world's most concentrated
gas hydrate fields. Discovered by Imperial Oil in 1971-72 with the
Mallik L-38 exploration well, gas hydrate saturations in the field
average more than 60 percent and, in some cases, exceed 90 percent
of the pore volume. Porosities in the poorly consolidated reservoir
average about 40 percent.
In 1998, the GSC was involved in the drilling of
Mallik 2L-38, a research well that identified at least 10 discrete
gas hydrate intervals, exceeding 110 meters in total thickness.
recognized that the natural laboratory was correct," said David
Boerner, an executive director of the GSC. "The consortium was built
around the basic idea that we had fairly easy access to a large,
known occurrence of gas hydrates."
Easy access for oil and gas exploration in Canada's
Northwest Territories means barging the drilling equipment 1,500
kilometers up the Mackenzie River during the summer to a staging
ground in the Mackenzie Delta.
It also means constructing 200 kilometers of ice
roads to transport the drilling equipment and camp to the Mallik
Scott Dallimore is a research scientist with the
Terrain Sciences Division of the GSC, and the scientific coordinator
of the 2002 Mallik research well project.
hydrates are amazing deposits that only exist at atmospheric pressures
for fleeting moments," Dallimore said.
"These compounds have not been extensively studied
Must Be Quick ...
Gas hydrates are white crystalline substances that
look and behave like dry ice, formed under conditions of low temperature
and high volume. Stable at only certain depths defined by temperature
and pressure regimes, gas hydrates brought to the earth's surface
in core barrels snap, crackle and pop at atmospheric pressure.
Researchers have to be quick -- gas hydrate cores
literally morph or dissociate into an oozy mess of free gas, water
and liquified sediments. If you're brave enough to light a match
near them, these ice-like sediments burst into flames.
"We worked in a chilled environment," Dallimore said
of the Mallik project. "Within 10 minutes, either using liquid nitrogen
or by repressurizing the samples, we stabilized and preserved the
gas hydrates for subsequent research projects."
JAPEX Canada Ltd. acted as the operator for the 79-day
project. The consortium -- consisting of 100 researchers and crew
members -- drilled the 1,166-meter Malik 5L-38 production well,
and two 1,188-meter observation wells offset 40 meters from the
Using the grid of three boreholes, cross-well tomographic
surveys, zero-offset and walk-away vertical seismic profiles were
conducted -- before, during and after production testing -- to measure
acoustic changes induced by production in the hydrate zone.
member Tim Collett, a research geologist with the geologic division
of the U.S. Geological Survey, participated in the Mallik 2002 field
"We put a known amount of heat into the reservoir
at a known rate, and measured the gas that came out," Collett said.
He described the production tests as "scientifically
controlled experiments which were not designed to maximize the volume
of gas produced from the gas hydrates."
The results of the consortium's ground-breaking research
will remain confidential until August 2004.
GSC published its first comprehensive inventory on gas hydrate distribution
and volume in Canada in the July 2001 AAPG BULLETIN, when authors
J.A. Majorowicz and K.G. Osadetz estimated that, on the high side,
in-place gas hydrate volumes sequestered in sediments in the continental
shelves, ocean margins and below terrestrial permafrost may approach
30 times those of conventional natural gas resource.
Composed primarily of natural gas or methane, hydrates
sometimes contain very minor percentages of ethane or propane. Originating
from both thermogenic and biogenic sources, methane gas migrates
from deep in the sedimentary section -- often along fault planes
and tectonic sutures in subduction zones -- until it encounters
near-freezing temperatures where it morphs into gas hydrates.
In the world's oceans, stable gas hydrates occur
beneath the sea floor where water depths exceed 300 meters. In the
Canadian North, permafrost often exceeds 200 meters in thickness,
creating a low geothermal gradient favorable to gas hydrate formation.
The gas hydrate structure -- one methane molecule
surrounded by a cage of six water molecules -- concentrates methane,
on a volume basis, 150 to 180 times the amount of methane found
in an equal volume of free gas at standard conditions.
As a greenhouse gas, methane has a heating capacity
of about 21 times that of carbon dioxide. Scientists, therefore,
are also studying gas hydrates at Mallik with respect to their role
in global climate change. Researchers are interested in the processes
that liberate large amounts of methane into the oceans from melting
permafrost and from seismically active sutures.
According to Dallimore, the gas hydrate stability
regimes and the sediment types are identical at Mallik and the Nankai
Trough, a subduction zone situated south of Japan in 950 meters
of water. That's why Takashi Uchida, a senior researcher with JNOC
and JAPEX in Tokyo, has been participating in the Mallik research
programs since 1998.
Uchida drilled six wells in the Nankai Trough in
2000, and is planning to drill an additional 30 wells in 2003.
"I believe that gas hydrates will supply natural
gas for Japan in the next 20 or 30 years," said Uchida, an AAPG
Gas hydrates represent a strategic energy resource
for Japan, a country that imports more than 99 percent of its oil
'Big as a VW Bug'
Serendipity often plays a role in scientific discovery;
oil and gas explorationists describe this phenomenon as "luck."
When a fishing dragger conducting experimental, deepwater
studies snagged several tons of gas hydrates in Barkley Canyon,
80 kilometers off the southwestern coast of Vancouver Island, the
hunt was on to find the mother lode.
Using the Canadian submersible ROPOS (Remotely Operated
Platform for Ocean Science), a team of geophysicists led by Ross
Chapman of the University of Victoria's School of Earth and Ocean
Science discovered the largest deposits of gas hydrates ever observed
on the sea floor off Canada.
Situated in 850 metres of water on the Pacific continental
margin, researchers estimate that the "mother loded" of gas hydrates
extends over four square kilometers.
Photographs taken by ROPOS illustrate what the geophysicists
describe as a gas hydrate glacier and associated mounds of pure
thermogenically sourced hydrates -- one mound was the size of a
Volkswagen Bug. Oil seeps were observed coming out of the gas hydrate
"To find any kind of hydrates preserved on the sea
floor is rare," explained Chapman, professor of ocean acoustics.
"There must be a huge flow from somewhere down below."
Collett echoed Chapman's sentiments -- gas hydrate
accumulations are a natural part of the petroleum system, he said.
"Gas hydrates seeps in the sea floor are telling
you that there's a deeper hydrocarbon deposit," he added. "Hydrates
imply that there's a leaky seal."
Since 1985, Collett has been the project chief of
the USGS' North Slope of Alaska Gas Hydrate Project. He believes
that the first gas hydrate production probably will be funded and
supported by producing the underlying free gas.
He points to the economic rationale of capitalizing
on the infrastructure in mature fields in the North Slope of Alaska:
- Producing the underlying free gas to depressurize
the gas hydrate zones above.
- Using existing boreholes for sidetracks
into gas hydrate zones.
- Reinjecting the hot water that's being
produced from deeper reservoir zones into the gas hydrate zones.
Collett speculates that if a gas pipeline had been
built 20 years ago to monetize the North Slope's stranded conventional
reserves, gas hydrate reserves would be producing today.
This is the case in the Messoyakha gas hydrate field
in Russia. Producing since the 1960s, the field contains a free
gas accumulation with an overlying gas hydrate seal. Production
of the free gas depressurizes the gas hydrates; in turn, gas liberated
from the gas hydrate reservoir recharges the conventional gas reservoir.
A parallel can be drawn between the future development
of gas hydrates and the historical development of other unconventional
energy sources: Fifty years ago, no technology existed to extract
the huge bitumen reserves contained in the oil sands of northern
Alberta. The Canadian oil and gas industry rose to the challenge,
developing several innovative extraction technologies.
"Canadians are pre-eminent at doing things in hostile
environments," Dallimore mused. "There's quite an astounding intellectual
base in Canada in the field of gas hydrates."
The construction of the 1,300-kilometer long Mackenzie
Valley Pipeline -- anticipated to begin within the next five years
-- may provide the necessary catalyst for economically producing
gas hydrates in the Canadian North.