--> --> Abstract: Multi-Component Seismic Data in Gas Hydrate Investigations, by Karin Andreassen, Karl A. Berteussen, Juergen Mienert, Helge Sognnes, Kerstin Henneberg, and Jan Langhammer; #90914(2000)

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Karin Andreassen1, Karl A. Berteussen2, Juergen Mienert1, Helge Sognnes2, Kerstin Henneberg3, Jan Langhammer3
(1) University of Tromso, Tromso, Norway
(2) PGS Reservoir, Oslo, Norway
(3) PGS Reservoir, Olso, Norway

Abstract: Multi-component seismic data in gas hydrate investigations

The presence of gas hydrates and free gas along the Norwegian continental margin is well documented in reflection seismic data. Results from this area suggest a correlation between hydrate instability and instabilities of the margin. It is, however, in order to understand the importance of hydrates for slope instability, necessary with reliable information about concentration and distribution of hydrates and associated free gas. Seismic methods seem to be the most promising approach for indirect detection and quantification of hydrates. It appears that hydrates may be detected by P-wave methods only if free gas exists at the base of the hydrate stability zone, giving rise to a bottom simulating reflection (BSR), but such methods seem to fail in detecting gas hydrates where the BSR is absent.

In order to test if P-S converted waves can add any significant contribution in the geohazard research, a seismic multi-component sea bottom line was acquired by PGS Reservoir over a well-defined BSR at the back wall of the Storegga Slide offshore of Norway. Since the gas hydrate-related BSR in this area has a different dip than the sediment layers, reflected events caused by gas hydrates can be separated from events caused by the sediment layers. Results from modeling the P-S conversions, from effective medium modeling, and from 2-D modeling have been compared with the real seismic data to estimate the amount of gas hydrate and associated free gas, and to investigate the potential for using converted waves in the detection and quantification of gas hydrates.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana