Characterizing Marine Gas-Hydrate Reservoirs and Determining Mechanical Properties of Marine Gas-Hydrate Strata with 4-Component Ocean-Bottom-Cable Seismic Data

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2002

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The research findings described in this report confirm that four-component ocean-bottom-cable (4-C OBC) seismic data provide valuable information about stratigraphy, lithofacies, and mechanical properties of sediments that cannot be extracted from conventional cable-towed P-wave marine seismic data. The key advantages of 4-C OBC data documented in this study that need to be considered for gas-hydrate applications are:

  1. The ability to image inside gas-hydrate P-wave wipeout zones with C waves;
  2. The increase in stratigraphic information that results from combining P-wave stratigraphic surfaces, seismic sequences, and seismic facies with C-wave stratigraphic surfaces, sequences, and facies;
  3. The increased spatial resolution of shallow seafloor strata that results when the time coordinates of C-wave data are warped (transformed) to P-wave image time coordinating;
  4. The mapping of lithofacies distributions using the lithofacies-sensitive velocity ratio, Vp/Vs; and
  5. The estimation of the spatially averaged mechanical strength of ocean-floor strata using interval values of Vp and Vs to calculate elastic moduli.

These technical advantages of 4-C OBC data will be discussed and illustrated in the main text of the report. Geologic and geophysical details developed during the investigation have been placed in appendices. The impact of the research findings can be understood by concentrating on the main text and ignoring the appendices. However, the appendices are important in that they document critical information and principles.

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