Gas Hydrates in the northern Gulf of Mexico

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Gas Hydrates in the northern Gulf of Mexico

• Out of Gas by Jane M. Sanders and
• Gas Hydrate Geohazard Assessment in the Northern
  Gulf of Mexico Using a Vertical Line Array by
  Erika Géresi, N.R. Chapman, T.M. McGee, and J.R.
  Woolsey

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What is gas hydrate?

• Gas hydrate is a solid, ice-like substance
  containing natural gasmostly methaneand water.
  Gas hydrates occur offshore on continental
  margins where nutrient-rich waters deliver
  organic detritus for bacteria to convert to
  methane and, to a lesser extent, in the
  permafrost sediments of Polar Regions.

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Why are gas hydrates important?

• They are a potential energy resource
• They may contribute to global warming
• They could represent a threat to deep-sea
  petroleum production

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Conditions Necessary to Gas Hydrate Stability

• Gas hydrates require the relatively low
  temperatures and high pressures found in
  sediments at water depths of about 500 meters.
• Most are found in sediments tens to hundreds of
  meters below the sea-floor.

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The Northern Gulf of Mexico

• There may be less gas hydrate in the northern
  Gulf of Mexico than previously estimated because
  of the presence of salt domes. The thermal
  properties of salt increases the temperature of
  the sediments, which, combined with the presence
  of salt in pore spaces, makes the formation of
  gas hydrates difficult.

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Potential Hazard

• The dissociation of solid gas hydrate to water
  and gas can result in sea-floor destabilization.
  It can cause large submarine landslides and even
  tsunamis.

• As natural gas and oil exploration moves into
  areas containing gas hydrates, drilling
  operations may cause gas hydrate melting,
  sediment instability, borehole collapse, and gas
  blowouts.

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How Gas Hydrates Relate to Sea-Floor Stability

• When gas hydrates form in the pore spaces of
  sediment, they support the sediments frame,
  thereby increasing its bearing capacity.

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Detecting the Presence of Gas Hydrates

• The conventional seismic techniques used to
  image the sea-floor often fail to accurately
  represent complex geological features.
• One of the new seismic data acquisition
  techniques is the Vertical Line Array.

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The Vertical Line Array

• The Vertical Line Array, or VLA, is part of the
  development leading to the Gas Hydrate Monitoring
  Station in the northern Gulf of Mexico.
• It uses propagation velocities, physical
  properties, and the acoustic character of the
  sub-bottom to create a more accurate image of
  complex areas, especially in the presence of gas
  hydrate.

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Why is the VLA important?

• In order to understand the consequences and
  causes of sea-floor insatiability in the presence
  of gas hydrate, it is imperative to understand
  the geological setting and the physical
  properties of the hydrates, and to be able to
  estimate the distribution and concentration of
  the gas hydrate deposits.

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Questions?
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Works Cited

• Out of Gas http//gtresearchnews.gatech.edu/re
  shor/rh-ss05/gas-hydrates.pdf
• Gas Hydrate Geohazard Assessment in the Northern
  Gulf of Mexico Using a Vertical Line Array
  http//www.searchanddiscovery.com/documents/2005/g
  eresi/index.htm
• Background picture for the first slide
  http//menlocampus.wr.usgs.gov/50years/accomplishm
  ents/images/tn-Flame_hydrate.jpg
• Background image for Questions slide
  http//www.gashydat.org/images/samples.gif