are ice-like minerals that form at the low temperatures and
high pressures in the deep sea. Hydrates contain gases, such
as hydrocarbons, that glue themselves inside symmetrical cages
of water molecules to form hydrate crystals. Research submarines
are the ideal tool to study hydrates under natural conditions.
Submarines make a profound difference in our understanding
of gas hydrate because they allow us to see hydrates forming
mounds on the seafloor. The mounds are covered with white
and orange bacterial mats as well as various filter-feeding
bivalves and other strange organisms. Mounds are sometimes
surrounded by rings of chemosynthetic organisms such as tube
worms and mussels. Actually, the seafloor scene from a research
submarine gives the strong visual impression of a silent,
serene, and beautiful garden.
gas hydrates contain hydrocarbons that are colorless, not
all of them are white like snow. Some hydrates from the deep
Gulf of Mexico are richly colored in shades of yellow, orange,
or even red. The ice-like masses are beautiful, and contrast
with the dull gray of deep sea muds. Hydrates from the Blake-Bahamas
Plateau in the Atlantic Ocean can be gray or blue. Scientists
would like to explain why hydrates show these colors, but
so far there is little agreement on reasons. A number of different
factors, including oil, bacteria, and minerals, are probably
at play in producing the rainbow hydrates .
all gas hydrates are found by drilling in sediments at 10s
to 100s of meters depth, but the gulf is different. The Gulf
of Mexico is the best natural laboratory in the world for
studying gas hydrates because they outcrop on the seafloor
as mounds and can be easily sampled in sediments.
aboard research vessels first found gas hydrates in the deep
waters of the gulf in 1983 by taking core samples at sites
where oil was naturally seeping out of the bottom. Hydrates
have since been recovered in cores from water depths as shallow
as 425 meters and at depths greater than 2000 meters.
captured in gas hydrates come from various sources. Methane
hydrates are the most abundant type in the earth's ocean.
They occur in deep water and on land in polar areas. A methane
molecule only contains one carbon atom and four hydrogen atoms
(CH4). It is a small molecule, and by itself can
form one simple type of hydrate, which is known as structure
I. Free methane gas appears to exist below hydrate in some
areas, sealed in by the overlying impermeable hydrate layer.
bacteria in marine sediments naturally produce enormous volumes
of methane when they feed on plant debris washed into the
gulf from rivers and swamps. This "biogenic" methane is often
trapped in layers of hydrate that simulate the contours of
the seafloor, and can be detected by various seismic techniques
commonly used in oil and gas exploration.
methane hydrates are most abundant, Texas A&M geochemists
find them the least interesting because the methane molecule
is so simple.
in the gulf
oil and gas seeps in the deep Gulf of Mexico also deliver
bigger hydrocarbon molecules to the seafloor. An exciting
discovery is that larger crystal forms of hydrate exist in
the gulf. One of these is structure II hydrate, which can
contain methane and other hydrocarbons such as propane, a
three-carbon hydrocarbon molecule normally found in petroleum
of thermal origin. Structure II hydrate was first produced
in laboratory experiments, then in 1983 we made the first
discovery of structure II hydrate in the natural environment
at a depth of 530 meters.
we discovered the first evidence of structure H hydrate in
nature at a similar water depth near Jolliet Field. This rare
hydrate forms "cages" large enough to hold molecules much
bigger than methane. For example, hydrates at Jolliet Field
contained abundant iso-pentane, a big, branched-chain hydrocarbon
molecule with five carbon atoms. We are excited by the real
possibility of discovering other, previously unknown types
of hydrate crystals in our natural laboratory, the Gulf of
no accident that unusual gas hydrates were discovered near
Jolliet Field, a site now occupied by a huge oil platform.
Oil and gas continually migrate from great depths in the earth's
crust toward the gulf floor. Some of the oil and gas is trapped
below the sea bottom, but much migrates toward the seafloor
where hydrates form. For this reason, natural oil and gas
seeps and their associated hydrates are studied as a guide
to the presence of subsurface fields.
sea surface, decomposing hydrate feels like cold Alka Seltzer
fizzing and popping on your skin. It's fun to light gas hydrates
with a match and watch the hydrocarbons burn like a candle,
leaving behind only slightly salty water. Watching gas hydrate
burn and produce heat shows its value as an energy source.
Right now there is worldwide interest in exploiting energy
estimates of the total energy reserves trapped in methane
hydrate vary considerably, but all the numbers emphasize this
single point-the resource potential of methane in gas hydrate
exceeds the combined worldwide reserves of conventional oil
and gas reservoirs, coal, and oil shale by a wide margin.
It is no secret that the world's production of conventional
fossil fuels will begin to decline sometime during the next
century. At that time, some oil companies may go extinct or
we might start referring to them as hydrate companies. A great
opportunity to develop new technology will occur, and ocean
scientists will have the chance to contribute to the future
of our energy supply during that time of change.
steps towards hydrate gas production will occur soon, with
the goal to recover natural gas by decomposing hydrates from
offshore deposits. A research team from India is getting ready
to begin an applied research effort to drill wells in deep
water, and to learn how to produce gas hydrates. Similar research
is proceeding offshore near Japan. The hydrate race has already
can be grown and carefully studied in the laboratory, but
the problem is that laboratory experiments are only simple
simulations. The experiments, being simple, are always outfoxed
by nature. For example, laboratory hydrates grow only slowly
and they are more like slush than ice.
gas hydrates on the deep seafloor for the first time in 1995,
using a research submarine in a natural setting (See "Voyage to the depths").
This pivotal experiment showed that hydrate can be rapidly
produced from natural gas venting into the sea, emphasizing
that economic exploitation of gas hydrates is actually closer
than we thought.
precipitation of gas hydrate on the gulf floor expands the
horizon for energy production. Until now, most thinking centered
on gathering hydrate known to be buried in sediments, and
allowing it to decompose into fuel and water. Our experiment
shows that there might be another way to use gas hydrates
to produce energy.
possible to drill for conventional gas reservoirs in the sea
at great water depths, but it is not always possible to produce
that gas because of economic problems associated with long
pipelines across unstable continental slopes. Furthermore,
pipelines in deep, cold water tend to become plugged with
hydrates. Energy companies actually support research to prevent
hydrates from forming!
an open mind about hydrates as a future energy source. Enormous
volumes of natural gas vent naturally to the deep waters of
the gulf and at many locations on continental margins offshore.
This natural gas supply currently goes unused, and eventually
escapes to the atmosphere. At the same time, conventional
gas reserves in ultra-deep water will probably never be produced
due to the high costs. Why not produce gas hydrates industrially
at the seafloor from escaping gas? Manufacturing hydrates
from gas currently being lost to the water column could help
buffer future energy shocks.
is a formidable obstacle to using hydrates as fuel. When removed
from its high pressure, low temperature environment hydrate
decomposes and releases the hydrocarbon gas contained in it.
We do not yet have a way to safely transport large amounts
of hydrate to production facilities on land.
approach to the hydrate transportation problem is to pelletize
hydrate or to inflate large bladder-like blimps with hydrate
in the deep sea. Submarines could then tow the hydrates to
shallower water near the continental shelf, where they could
be slowly decomposed to yield fuel and water. Perhaps chemical
engineers could design additives to make hydrates more stable
at lower pressures and higher temperatures. If they can, hydrate
might actually be safer to transport in conventional ships
than liquefied natural gas.
hydrates from naturally venting gas has implications for global
warming with respect to two greenhouse gases, methane and
carbon dioxide. Methane is the main constituent of gas hydrates,
and is also a fast acting, high-impact greenhouse gas. Methane
is at least an order of magnitude more effective as a short-term
greenhouse gas than carbon dioxide. Although it is a matter
of controversy among scientists, gas hydrates could have impacted
the atmosphere several times during the last two million years.
Some believe that fluctuating sea levels of the ice ages could
have rendered large volumes of gas hydrate unstable, releasing
great volumes of methane to the atmosphere.
gas hydrates would redirect methane away from the atmosphere.
Using hydrate methane industrially would convert it to carbon
dioxide, actually decreasing the short-term effect on atmospheric
chemistry and global change. In addition, methane is an environmentally
cleaner fuel than oil, coal, or oil shale which all have an
immense environmental impact during production and combustion.
dioxide itself is a gas that forms hydrates. Much recent research
focuses on understanding how to deliberately create carbon
dioxide hydrates. Perhaps we can find a way to trap carbon
dioxide at the seafloor where it would eventually be buried
natural gas reservoirs in Southeast Asia contain more carbon
dioxide than hydrocarbons. Normally the carbon dioxide would
be separated from the hydrocarbon gas and released to the
atmosphere. Separating carbon dioxide at the seafloor and
burying it as hydrate would be more environmentally friendly.
there is a bright future for gas hydrate research to ensure
future supplies of clean-burning energy, to potentially dispose
of greenhouse methane, and to understand the role of hydrates
as an agent of climate change over geologic time. The question
of hydrates as a niche habitat for life also deserves special
study (See "Lair of the 'Ice Worm'").
We look forward to addressing these questions in future research
In the serene hydrate environment colorful mats of bacteria
blanket sediment over and around a hydrate mound, surrounded
by tendril-like tubes of chemosynthetic worms. Free hydrocarbon
gas bubbles out of the sediment to begin its 540-meter ascent
to the sea surface (Photo by Jonathan Blair).
[26K] Scientists find hydrates around hydrocarbon seeps in
the Gulf of Mexico. The seeps often signal the presence of
oil and gas reservoirs far below the seafloor.
This mound of gas hydrate grew large enough to break free
of the seafloor's surface. Sediment still drapes the top of
the mound but on its underside the hyrate burrows of ice worms
lie exposed. (Photo by Charles Fisher)
I hydrate crystals form cages that can only hold small hydrocarbon
molecules inside. These commonly hold a single molecule of
with more complex structures can contain larger hydrocarbon
molecules. We predicted Structure II hydrates would exist
based on laboratory experiments, then discovered them in nature
at Jolliet Field in the Gulf of Mexico.
H crystal cages can contain iso-pentane, a relatively large,
Texas A&M oceanographer Ian MacDonald prepares a pressurized
container in which to store hydrates for later study in the
laboratory. Without the specially designed canister hydrates
decompose into gas and water as they are raised from the bottom.
(Photo by Charles Fisher)
colorized image of the ocean surface taken from the space
shuttle makes the sea and clouds look like an artist's abstract
dabs and brushstrokes. The bright streaks are oil slicks produced
by hydrocarbons seeping naturally from seafloor vents.