Transcript Gas Hydrates - Texas Coastal Erosion Data Network

Gas Hydrates
History
 Why the interest?
 Chemical Aspects
 Biology
 Geology
 Utilization as a Fuel Source and Future
Development

History

Discovered in late 19th century
in Siberian permafrost

Known to form pipeline
blockages for years
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“Rediscovered” as oil
exploration moved offshore in
early 1970’s
• Why the sudden interest?
•
The fuel of the next century?
• Worldwide reserves estimated to be
400-500 million trillion cubic
feet(tcf)
• 5000 tcf of known natural gas
reserves worldwide
Map of in-situ hydrate locations
• USA has gas hydrate reserves
estimated between 112000 tcf and
676000 tcf
• USA has 1400 tcf of natural gas
reserves
• USA uses 25-30 tcf/yr of natural gas
Carbon reserves vs gas hydrates
•Chemical Aspects of
Gas Hydrates
• Ice-like crystaline mineral
• 1 cubic meter of gas hydrate (90% site
occupied) = 163 m3 of gas + .87 m3
• Clathrates or Clathrate Hydrates
• Three Structure Types: I, II, H
• Structure type determines gas type
• Scientist don’t fully understand the physics
of gas hydrate formation
• Structure I Gas Hydrate
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Crystal - Cubic Lattice
Can hold only small
molecules (5.2 angstroms or
less) such as ethane(C2H6)
and methane(CH4)
Biogenic in origin
• Structure II Gas Hydrate
Crystal-Diamond Lattice
• May contain larger
molecules (5.9-6.9
angstroms) such as
propane(C3H8) or
isobutane(C4H10)
• Thermogenic in origin
• Structure H Gas Hydrate
•
•
Crystal - Hexagonal Lattice
Rare
Able to hold much larger
molecules such as isopentane
A Little Chemistry
• Environmental
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•
Concerns
Formation of hydrates
from gas vent flumes
Contribution to
greenhouse effect?
Hydrates Support Dense
Biological Communities
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Bacterial mats
Tube worms
Mussels
Shrimp
Crabs
Fish
Eels
Isopods
Polychaetes (the newly discovered “Ice Worm”)
Sediment Failure
http://www.earthinstitute.columbia.edu/news/aboutStory/pdf/28-407.pdf
Eruptions
Hydrate Ridge
Storegga Slides
LOCATION OF GAS HYDRATES
Using seismic-reflection
• Seismic-reflection Profile
• Side Scan Sonar
Coring
http://www.ngdc.noaa.gov/mgg/bathymetry/relief.html
using seismic-reflection profiles
Bottom Simulating Reflection (BSRs)
http://woodshole.er.usgs.gov/project-pages/hydrates/hydrate.htm
Side-Scan Sonar
http://gulftour.tamu.edu/cruise_background2.html
Coring
http://www.hydrate.org/about/geology.cfm#Where%20Found
The Future

USA has suggested in 2000 that $47.5 million be
used to explore the option of gas hydrates over
a five year period.
 Japan has enormous offshore deposits and
plans to have production on line by 2015 ($60
million on research)
 India is also looking into converting its offshore
deposits ($50 million on research)
 Germany, France, and Australia also starting to
fund research
Challenges of Hydrate
Utilization as a Fuel Source

Hydrates decompose releasing hydrocarbons as a gas
when removed from low temp/high pressure
environment

High costs of long pipelines across unstable continental
slopes

Pipelines in deep cold water become plugged with
hydrates during transport

Damage to sensitive chemosynthetic communities
Potential New Approaches
to Transport Hydrates
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Pelletize the hydrate
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Inflate large bladder-like blimps with hydrate and
tow to shallower water to allow a slow controlled
decomposition
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Additives to stabilize hydrates at lower pressures
and higher temperature environments for safer
transport by ships
Advantages of Hydrates as a
Fuel
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Denser source of hydrocarbons than conventional sources
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Amount of conventional fossil fuels will decline in next century
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Redirect/dispose of greenhouse methane away from the
atmosphere
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Cleaner fuel source than oil, coal, and oil shale
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Abundant supplies in deep sea and permafrost