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Abstract

Geresi, E., R. Chapman, T. McGee, and B. Woolsey, 2009, Monitoring sea-floor instability caused by the presence of gas hydrate using ocean acoustical and geophysical techniques in the northern Gulf of Mexico, in T. Collett, A. Johnson, C. Knapp, and R. Boswell, eds., Natural gas hydrates—Energy resource potential and associated geologic hazards: AAPG Memoir 89, p. 287–296.

DOI:10.1306/13201106M893344

Copyright copy2009 by The American Association of Petroleum Geologists.

Monitoring Sea-floor Instability Caused by the Presence of Gas Hydrate Using Ocean Acoustical and Geophysical Techniques in the Northern Gulf of Mexico

Erika Geresi,1 Ross Chapman,2 Tom McGee,3 Bob Woolsey4

1School of Earth and Ocean Sciences, University of Victoria, British Columbia, Canada
2School of Earth and Ocean Sciences, University of Victoria, British Columbia, Canada
3The Center for Marine Resources and Environmental Technology (CMRET), University of Mississippi, Oxford, Mississippi, U.S.A.
4The Center for Marine Resources and Environmental Technology (CMRET), University of Mississippi, Oxford, Mississippi, U.S.A.

ACKNOWLEDGMENTS

The prototype VLA was designed and constructed by Specialty Devices Inc. of Plano, Texas. Its design and testing and the reveal research were funded by Minerals Management Service, U.S. Department of Interior, Herndon. Its construction was funded by the National Energy Technology Laboratory, U.S. Department of Energy, Morgantown. The specialized data processing was partially done with Lookout Geophysical Company Software of Palisade, Colorado, by Erika Geresi, University of Victoria. Special thanks to the USGS for the use of their data.

ABSTRACT

The northern Gulf of Mexico is characterized by an extremely heterogeneous near-surface geology that makes the geophysical identification of subsurface gas hydrate challenging, and the interpretation of data is commonly ambiguous. This chapter describes a set of novel seismic experiments designed to characterize the subsurface hydrate distribution at Mississippi Canyon Block 798 (MC798) in the northern Gulf of Mexico.

A vertical line array (VLA), specially designed for high resolution in shallow sediments, was deployed by the Center for Marine Resources and Environmental Technology (CMRET) with the general objectives of (1) acquiring very high-resolution seismic reflection profiles in 850 m (2789 ft) of water depth, (2) studying the acoustic character and features of the sea floor for evidence of sea-floor hazards, and (3) looking for evidence of subsurface gas hydrates and their properties.

Comparisons were made of the results of several seismic experiments in the area of interest in MC798, including the prototype VLA test in 2003, and conventional multi- and single-channel seismic data from previous years. In this article, these data sets were integrated to show the improved resolution of the near-surface sediments in the VLA data. Two interpretations of the geology are given; the evidence for the presence of subsurface gas hydrate is ambiguous.

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