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Abegg, Friedrich1, Johannes Freitag2, Gerhard Bohrmann3, Warner Brueckmann4
(1)GEOMAR Research Center for Marine Sciences, Kiel, Germany
(2)Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
(3)University of Bremen, Bremen,
(4)GEOMAR, Kiel,

ABSTRACT: Free Gas and Gas Hydrate: Proof of the Coexistence in Marine Environment and Implication for the Hydrate Formation

Recent advance in the investigation of the internal gas hydrate structure and in small-scale quantification is based on a combination of a new coring device and computerised X-ray tomography (CT). This approach has been chosen because gas hydrate is only stable within a low temperature and high pressure field. A MultiAutoclaveCorer, developed by the Technical University of Berlin, is in principle similar to a piston corer and has the size of a multiple corer. During the deployments on Hydrate Ridge off the Oregon coast, two pressure vessels filled with seafloor samples could be recovered. They were CT-investigated after the cruise in a medical clinic four days after recovery.
As a result, a 3D-dataset of the cores is available which allows to quantify the components gas hydrate, sediment and free gas and also shows the distribution and orientation of the gas bubbles. One of the pressure vessels showed a distinct gas hydrate horizon where the gas hydrate content reached close to 50 vol %. Within this horizon there was a free gas content of 2.4 vol %. The preferential bubble orientation of this sample, compared to free gas in soft marine sediments, is horizontal, not vertical, which is an indicator for the mechanisms of gas transport and hydrate formation.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.