Multicomponent Seismic Studies of the Gas-hydrate System at the Storegga Slide
Stefan Bünz, Jürgen Mienert, Karin Andreassen, 2009. "Multicomponent Seismic Studies of the Gas-hydrate System at the Storegga Slide", Natural Gas Hydrates—Energy Resource Potential and Associated Geologic Hazards, T. Collett, A. Johnson, C. Knapp, R. Boswell
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A multicomponent seismic technology is able to broaden our knowledge of the gas-hydrate reservoir. In the marine environment, shear waves (S waves) can be generated by conversion from a downward-propagating compressional wave (P wave) on reflection at a sedimentary interface. The upward-propagating S wave can be recorded at the ocean floor using horizontal geophones. S waves can be useful in addition to P-wave data because the S-wave velocity is slower than P-wave velocity and S waves are less affected by the pore fill of porous rocks. This clearly gives a distinct improvement because (1) seismic resolution using S waves increases, (2) targets of gas or of poor P-wave reflectivity are imaged well, (3) pore fluids and lithology can be discriminated, and (4) the enhanced ability exists to estimate gas-hydrate concentrations. On the mid-Norwegian margin, multicomponent seismic data have enabled us to choose a proper rock-physical model for the hydrate-bearing sediments. We are able to constrain seismic velocities from ocean-bottom seismic data. This allows us to obtain more accurate estimations of gas-hydrate and free-gas concentrations and to assess the occurrence of overpressures within the gas-bearing sediments underneath the hydrates. Improved acoustic images look through the zone underneath the hydrate-bearing sediments, which is obscured on the P-wave data because of the occurrence of gas.
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In September 2004, the American Association of Petroleum Geologists (AAPG) convened a Hedberg Research Conference in Vancouver, British Columbia, Canada titled "Natural Gas Hydrates: Energy Resource Potential and Associated Geologic Hazards." As a continuation of the Hedberg Research Conference in Vancouver, the conveners of the conference and the editors of this Memoir have worked with more than 150 authors and coauthors to prepare this Memoir on gas hydrates. This publication follows the goals of the Hedberg conference; however, the contents of this Memoir were expanded to include all aspects of gas hydrates in nature. This Memoir contains 39 individual contributions, ranging from long topical summaries to shorter focused research papers. This Memoir has been published in two parts, with digital versions of all the complete research papers included on the enclosed CD. The hardcopy portion of the Memoir includes abstracts and several key figures for each of the contributions along with a complete copy of a gas hydrate technical review. The digital portion of this Memoir has been organized into a series of topical sections consisting of review articles, marine gas hydrate papers, and gas hydrate laboratory and modeling studies. Because of the rapidly emerging worldwide interest in gas hydrates, this comprehensive treatise on the geology of gas hydrates will be valuable to both the gas hydrate research community and exploration/development geologists working in arctic and deep marine environments.