Gas Hydrates

1
Gas Hydrates

• History
• Why the interest?
• Chemical Aspects
• Biology
• Geology
• Utilization as a Fuel Source and Future
  Development

2
History

• Discovered in late 19th century in Siberian
  permafrost
• Known to form pipeline blockages for years
• Rediscovered as oil exploration moved offshore
  in early 1970s

3

• Why the sudden interest?
• The fuel of the next century?

4

• 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
5

• 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

6

• Chemical Aspects of Gas Hydrates

7

• 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 dont fully understand the physics of
  gas hydrate formation

8

• Structure I Gas Hydrate Crystal - Cubic Lattice
• Can hold only small molecules (5.2 angstroms or
  less) such as ethane(C2H6) and methane(CH4)
• Biogenic in origin

9

• 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

10

• Structure H Gas Hydrate Crystal - Hexagonal
  Lattice
• Rare
• Able to hold much larger molecules such as
  iso-pentane

11
A Little Chemistry

• Environmental Concerns
• Formation of hydrates from gas vent flumes
• Contribution to greenhouse effect?

12
Hydrates Support Dense Biological Communities

• Bacterial mats
• Tube worms
• Mussels
• Shrimp
• Crabs
• Fish
• Eels
• Isopods
• Polychaetes (the newly discovered Ice Worm)

13
Sediment Failure

http//www.earthinstitute.columbia.edu/news/aboutS
tory/pdf/28-407.pdf
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Eruptions
Hydrate Ridge Storegga Slides
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LOCATION OF GAS HYDRATES

• Using seismic-reflection
• Seismic-reflection Profile
• Side Scan Sonar
• Coring

http//www.ngdc.noaa.gov/mgg/bathymetry/relief.htm
l
16
using seismic-reflection profiles
Bottom Simulating Reflection (BSRs)
http//woodshole.er.usgs.gov/project-pages/hydrate
s/hydrate.htm
17
Side-Scan Sonar
http//gulftour.tamu.edu/cruise_background2.html
18
Coring
http//www.hydrate.org/about/geology.cfmWhere20F
ound
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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

20
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

21
Potential New Approaches to Transport Hydrates

• Pelletize the hydrate
• Inflate large bladder-like blimps with hydrate
  and tow to shallower water to allow a slow
  controlled decomposition
• Additives to stabilize hydrates at lower
  pressures and higher temperature environments for
  safer transport by ships

22
Advantages of Hydrates as a Fuel

• Denser source of hydrocarbons than conventional
  sources
• Amount of conventional fossil fuels will decline
  in next century
• Redirect/dispose of greenhouse methane away from
  the atmosphere
• Cleaner fuel source than oil, coal, and oil shale
• Abundant supplies in deep sea and permafrost