Hearing on Bill HR 1753 - 'Methane Hydrate Research
and Development Act of 1999'
Testimony of
Bilal U. Haq
Division of Ocean Sciences
National Science Foundation
Before the House Committee on Resources
ubcommittee for Energy and Minerals
May 25, 1999
Thank you, Madam Chairman, for giving me the opportunity
to present to the Subcommittee an outline of the state
of our knowledge of natural gas hydrates.
Natural gas hydrates have been known to exist within
the continental margin sediments for several decades
now, however, it is only during the last decade that
the pace of research into their distribution and nature
has picked up, and especially in the last three or
four years. The research effort in several countries
has been focused at learning more about their efficacy
as an alternative energy resource. In addition, their
role in slope instability and global climate change
is also of considerable interest to the research community
and has obvious societal relevance.
Gas hydrates consist of a mixture of methane and water
and are frozen in place in marine sediments on the
continental slope and rise. To be stable the hydrates
require high pressure and low bottom temperature and
thus they occur mostly at the depths of the continental
slope (generally below 1500 feet depth). Due to the
very low temperatures in the Arctic, hydrates also
occur on land associated with permafrost, and at shallower
submarine depths of about 600 feet. Methane gas that
forms the hydrate is mostly derived from the decay
of organic material trapped in the sediments.
Methane is a clean burning fuel. Because the methane
molecule contains more hydrogen atoms for every carbon
atom, its ignition produces less carbon dioxide than
other, heavier, hydrocarbons. In addition, the hydrate
concentrates 160 times more methane in the same space
as free gas at atmospheric pressure at sea level.
Thus, natural gas hydrates are considered by many
to represent an immense, environmentally friendly,
and viable, though as yet unproven, resource of methane.
In marine sediments, hydrates are commonly detected
by the presence of acoustic reflectors, known as bottom
simulating reflectors, or BSRs. However, to produce
a boundary that reflects acoustic energy, a significant
quantity of free gas needs to be present below the
hydrate to induce the contrast that causes the reflector.
BSRs are known from many continental margins of the
world, but hydrates have only rarely been sampled
through drilling. Moreover, the presence or absence
of BSR does not always correlate with the presence
of hydrate nor provide information about the quantity
of hydrate present. The general lack of direct sampling
means that estimating the volumes of methane trapped
in hydrates, or the associated free gas beneath the
hydrate stability zone, remains largely speculative.
One of the few places in the world where hydrates have
been drilled and directly sampled is on the Blake
Ridge, a topographic feature off the coast of the
Carolinas, Georgia and Florida. Here it was observed
that the BSR is present only where there is a significant
amount of free gas below the hydrate, whereas hydrate
was present even where there was no BSR recorded on
acoustic profiles. Thus, if our estimates are calculated
purely on the basis of observed BSRs, it may lead
to underestimation of the lateral extent of the hydrate
fields and the total volume of the contained methane.
Estimates of how much methane might be trapped in the
hydrates in the nearshore sediments therefore remain
conjectural at the present, but even the relatively
conservative estimates contemplate as much as double
the amount of all known fossil fuel sources. Whether
or not these large estimates can be translated into
a viable energy resource is a crucial question that
has been the focus of researchers in many countries.
In the past, petroleum industry in the US and elsewhere
has been less interested in methane hydrates as a
resource because of the difficulties in estimating
and extracting the gas and distributing it to consumers
as a cost-effective resource.
Since gas hydrates in marine sediments largely occur
on the continental slope, they may also be implicated
in massive slumps and slides when hydrates break down
due to increased bottom temperature or reduced hydrostatic
pressure. Local earth tremors may also cause hydrates
to slump along zones of weakness. When a hydrate dissociates,
its bottom layer changes from solid "icy" substance
to a "slushy" mixture of sediment, water and gas.
This change in the mechanical strength of the hydrate
occurs first near the base because the temperature
in the sediment increases with depth and thus the
bottom part of the hydrate stability zone is most
vulnerable to subtle changes in temperature and pressure.
This encourages massive slope failure along low-angle
detachment faults. Such slumps can be a considerable
hazard to petroleum exploration structures such as
drilling rigs and to undersea cables. In addition,
extensive slope failures can conceivably release large
amounts of methane gas into the seawater and atmosphere.
Scientists studying the recent geological past theorize
that gas-hydrate dissociation during the last glacial
period (some 18,000 years ago) may have been responsible
for the rapid termination of the glacial episode.
During the glacial period the sea level fell by more
than 300 feet, which lowered the hydrostatic pressure,
leading to massive slumping that may have liberated
significant amount of methane. Methane being a potent
greenhouse gas (considered to be ten times as potent
as carbon dioxide by weight), a large release from
hydrate sources could have triggered greenhouse warming.
As the frequency of slumping and methane release increased,
a threshold was eventually reached where ice melting
began, leading to a rapid deglaciation.
At present, however, the response of the methane trapped
in the permafrost as hydrate is of greater concern.
If the summer temperatures in the higher latitudes
were to rise by even a few degrees, it could lead
to increased emission of methane from the permafrost,
thereby adding to the greenhouse effect and further
raising the global temperatures. These increases in
global mean temperature may also lead to further melting
of high-latitude ice fields on Greenland and Antarctica.
The response of both the permafrost and the ice fields
to increased temperature, however, remains largely
unknown at the present time.
Direct measurements of methane in hydrated sediments
and the free gas below made during drilling on the
Blake Ridge by the Ocean Drilling Program, supported
largely by the National Science Foundation, show that
large quantities of methane may be stored in this
gas-hydrate field, and even more as free gas below
the hydrate. In the hydrate stability zone the volume
of the gas hydrate based on direct measurements was
estimated to be between 5 and 9% of the pore space.
Though the hydrate occurs mostly finely disseminated
in the sediment, relatively pure hydrate bodies up
to 30 cm thick also occur intermittently. Below the
hydrate stability pore spaces are saturated with free
gas. From the point of view of recoverability, the
free gas below the hydrate stability zone, if it occurs
in sufficient quantities, could be recovered first.
Eventually, the gas hydrate may itself be dissociated
artificially and recovered through injection of hot
water or through depressurization.
Although the hydrocarbon industry has had a long-standing
interest in hydrates (largely because of their nuisance
value in clogging up gas pipelines in colder high
latitudes and in seafloor instability for rig structures),
their slowness in responding to the need for gas-hydrate
research as an energy resource stems from several
factors. Many in the industry believe that the widely
cited large estimates of methane in gas hydrates on
the continental margins may be overstated. Moreover,
if the hydrate is thinly dispersed in the sediment
rather than concentrated, it may not be easily recoverable,
and thus not cost-effective to exploit.
One suggested scenario for the exploitation of such
a dispersed resource is excavation, which is environmentally
a less acceptable option than drilling. And finally,
if recovering methane from hydrate becomes feasible,
it may have important implications for slope stability.
Since most hydrates occur on the continental slope,
extracting the hydrate or recovering the free gas
below the stability zone could cause slope instabilities
of major proportions that may not be acceptable to
coastal communities. Producing gas from gas hydrates
locked up in the permafrost has so far met with considerable
difficulties, as the Russian efforts to do so in Siberia
in the 1960s and 70s would imply.
The occurrence and stability of gas hydrates at oceanic
depths of the slope and rise has also led to the notion
that we may be able dispose off excess green-house
gases, especially carbon dioxide, in the deep ocean
as artificial hydrates. Although permanent sequestration
of carbon dioxide may not be realistic since the hydrate
on the seafloor would eventually be dissolved and
dispersed in seawater, the isolation of carbon dioxide
in the form of solid hydrate that remains stable for
relatively long periods of time may be plausible.
The long time scales of ocean circulation, the large
size of the oceanic reservoir and the buffering effect
of carbonate sediments all speak in favor of this
potentiality. These notions, however, need considerable
measure of research, both in the laboratory and the
field, before they can be regarded as practical.
Research Needs
Much of the uncertainty concerning the value of gas
hydrates as a resource for the future, their role
in slope instability and their potential as agents
for future climate change, stems from the fact that
we have little knowledge of the nature of the gas-hydrate
reservoir. Understanding the characteristics of the
reservoir and finding ways to image and evaluate its
contents remotely may be the two most important challenges
in gas-hydrate R&D for the near future.
We need to know where on land and the continental margins
gas hydrates occur and how extensive is their distribution?
We need to be able to discern how they are distributed
-- mostly thinly dispersed in sediments or in substantial
local concentrations? Only then will we be able to
come up with meaningful estimates of their total volume
on the US continental margins and in higher latitudes,
as well their global distribution.
We also need a better understanding of how hydrates
form and how they get to where they are stabilized.
This effort encompasses learning more about the biological
activity and organic-matter decay that generates methane
for hydrates, their plumbing systems, migration pathways
and the hydrate thermodynamics, and it will require
laboratory experimentation, field observations and
modeling.
To understand the role of gas hydrates in slope instability,
research will be needed to learn more about their
physical properties and their response to changes
in pressure-temperature regimes. Both laboratory experimentation
and in situ monitoring will be necessary. Gas hydrates
in the Arctic, Gulf of Mexico and off the US East
Coast represent extensive natural laboratories for
all aspects of gas hydrate research.
To appreciate the role of gas hydrates in global climate
change, we need to have a better grasp of how much
of the hydrate in the continental margins and the
permafrost is actually susceptible to oceanic and
atmospheric temperature fluctuations. More importantly,
we must understand the fate of the methane released
from a hydrate source into the water column and the
atmosphere. Studies of the geological records of past
hydrate fields can also provide clues to their behavior
and role in climate change.
Once the efficacy of natural gas hydrate as a resource
has been proven, new technologies will have to be
developed for their meaningful exploitation. This
includes new methodologies for detection, drilling,
and recovery of the solid hydrate and the free gas
below. Such technologies are lacking at the present
time.
Madam Chairman, once again thank you for giving me
the opportunity to testify and I will be happy to
answer any questions from the members of the Subcommittee
that I am able to.
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