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Marine Geophysical Research

, Volume 39, Issue 1–2, pp 323–347 | Cite as

Improved detection and mapping of deepwater hydrocarbon seeps: optimizing multibeam echosounder seafloor backscatter acquisition and processing techniques

  • Garrett A. Mitchell
  • Daniel L. Orange
  • Jamshid J. Gharib
  • Paul Kennedy
Original Research Paper

Abstract

Marine seep hunting surveys are a current focus of hydrocarbon exploration surveys due to recent advances in offshore geophysical surveying, geochemical sampling, and analytical technologies. Hydrocarbon seeps are ephemeral, small, discrete, and therefore difficult to sample on the deep seafloor. Multibeam echosounders are an efficient seafloor exploration tool to remotely locate and map seep features. Geophysical signatures from hydrocarbon seeps are acoustically-evident in bathymetric, seafloor backscatter, midwater backscatter datasets. Interpretation of these signatures in backscatter datasets is a fundamental component of commercial seep hunting campaigns. Degradation of backscatter datasets resulting from environmental, geometric, and system noise can interfere with the detection and delineation of seeps. We present a relative backscatter intensity normalization method and an oversampling acquisition technique that can improve the geological resolvability of hydrocarbon seeps. We use Green Canyon (GC) Block 600 in the Northern Gulf of Mexico as a seep calibration site for a Kongsberg EM302 30 kHz MBES prior to the start of the Gigante seep hunting program to analyze these techniques. At GC600, we evaluate the results of a backscatter intensity normalization, assess the effectiveness of 2X seafloor coverage in resolving seep-related features in backscatter data, and determine the off-nadir detection limits of bubble plumes using the EM302. Incorporating these techniques into seep hunting surveys can improve the detectability and sampling of seafloor seeps.

Keywords

Midwater plume Green Canyon Block 600 Kongsberg EM302 Chemosynthetic Seafloor 

Notes

Acknowledgements

We acknowledge and thank the captains, crew, and technical staff of the Fugro Americas and Fugro Brasilis, in particular Michael Soebetki, Chris Trebaol, Brandt Broussard, and Robert Pritts who performed the backscatter normalization and processed the multibeam data. We thank the ECOGIG organization, in particular Mandy Joye and Geoff Wheet for the use of the their AUV datasets, ONE LLC and TGS Inc. for technical and financial support of the Gigante and Otos seep surveys. We also thank the guest editors of this special issue, Xavier Lurton and GeoffroyLamarche for their patience while this manuscript was being prepared in between multiple offshore seep surveys. We acknowledge and thank the reviewers for their constructive suggestions in improving the manuscript. This work was supported by Fugro USA.

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Copyright information

© Springer Science+Business Media B.V., part of Springer Nature 2018

Authors and Affiliations

  • Garrett A. Mitchell
    • 1
  • Daniel L. Orange
    • 2
  • Jamshid J. Gharib
    • 1
  • Paul Kennedy
    • 3
  1. 1.Fugro USA Marine, Inc.HoustonUSA
  2. 2.Oro Negro Exploration LLCSanta CruzUSA
  3. 3.Fugro Survey PtyWest PerthAustralia

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