We used single-component, high-frequency (1–10 kHz), chirp-sonar data acquired with autonomous underwater vehicle (AUV) technology and multicomponent, low-frequency (10-150 Hz) seismic data acquired with a standard surface-based air gun source and 4-component oceanbottom-cable (4C OBC) technology to study two fluid-gas expulsion sites across a portion of the Green Canyon area of the Gulf of Mexico (GOM). One expulsion site was in Green Canyon Block 204 (GC 204) near Genesis Field in Green Canyon Block 205 (GC 205), and the second was near Typhoon field, which produces from Green Canyon Block 237 (GC 237). We found that the lower-frequency OBC P-SV seismic images produced by our specialized 4C seismic dataprocessing concepts revealed features of near-seafloor geology with a spatial resolution equivalent to that of kHz-range AUV chirp-sonar data. We processed and interpreted more than 90 km of 2D4C OBC data extending across two expulsion features we selected for study. This paper describes the multicomponent, multifrequency seismic technology we used in this study and summarizes the near-seafloor geology defined by these technologies across these two expulsion features.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2007OBC sensor response and calibrated reflectivityAuthors: Milo M. BackusPaul E. MurrayRobert J. GraebnerBob A. HardageMilo M. BackusExploration Geophysics Laboratory, Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at AustinSearch for more papers by this author, Paul E. MurrayExploration Geophysics Laboratory, Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at AustinSearch for more papers by this author, Robert J. GraebnerExploration Geophysics Laboratory, Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at AustinSearch for more papers by this author, and Bob A. HardageExploration Geophysics Laboratory, Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at AustinSearch for more papers by this authorhttps://doi.org/10.1190/1.2792582 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Given deep‐water OBC data, we can combine hydrophone (P) and vertical‐geophone (Z) data to separate upgoing and downgoing acoustic wavefields. By using the downgoing wavefield to estimate the seismic wavelet, we can recover compressional‐wave reflectivity and provide an acoustic impedance log for the near‐seafloor sedimentary section. This procedure requires the calibration of geophone response to hydrophone response with an appropriate matching filter (z2p). P and Z data containing only upgoing energy can be provided in several ways to estimate z2p and p2z filters. Alternatively, the multiple/primary ratio (in the frequency domain) can be used to obtain calibrated reflectivity from the hydrophone alone or from the geophone alone, with no sensor calibration required. We apply these methods to a deep‐water OBC line. We obtain consistent results by all of the methods. By combining low‐frequency (5–70 Hz) z2p filters based on energy arriving before the direct arrival, with high‐frequency (25–180 Hz) z2p filters based on near‐offset reflection data, we can provide broadband (5–180 Hz) calibrated reflectivity and impedance of shallow seafloor sediments.Permalink: https://doi.org/10.1190/1.2792582FiguresReferencesRelatedDetailsCited ByDeep-water subsurface imaging using OBS interferometryOlivier Carrière and Peter Gerstoft4 February 2013 | GEOPHYSICS, Vol. 78, No. 2Wavefield-separation methods for dual-sensor towed-streamer dataAnthony Day, Tilman Klüver, Walter Söllner, Hocine Tabti, and David Carlson20 March 2013 | GEOPHYSICS, Vol. 78, No. 2Dual‐sensor streamer data: Calibration, acquisition QC and attenuation of seismic interferences and other noisesGuillaume Cambois, David Carlson, Craig Jones, Marina Lesnes, Walter Söllner, and Hocine Tabti14 October 2009Improving sensor technology brings a new level of reservoir understandingMasahiro Kamata, Les Nutt, and William Underhill15 December 2008 SEG Technical Program Expanded Abstracts 2007ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2007 Pages: 3124 publication data© 2007 Copyright © 2007 Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished: 14 Sep 2007 CITATION INFORMATION Milo M. Backus, Paul E. Murray, Robert J. Graebner, and Bob A. Hardage, (2007), "OBC sensor response and calibrated reflectivity," SEG Technical Program Expanded Abstracts : 1044-1048. https://doi.org/10.1190/1.2792582 Plain-Language Summary PDF DownloadLoading ...

The world's offshore continental margins contain vast reserves of gas hydrate, a frozen form of natural gas that is embedded in cold, near-seafloor strata. Published estimates suggest that the energy represented by gas hydrate may exceed the energy available from conventional fossil fuel by a factor of 2 or more. Understanding marine hydrate systems has become critical for long-term worldwide energy planning. Groups in several nations are attempting to evaluate the resource and to define seafloor stability problems across hydrate accumulations.

Multicomponent seismic data have unique value for studying near-seafloor geology in deepwater environments. When properly processed, PP (compressional) and PS (converted-shear) images made from multicomponent seismic data acquired in deepwater with seafloor sensors show near-seafloor geology with impressive detail. These high-resolution images are invaluable for studying deepwater gas-hydrate systems.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2005Enhanced PS‐wave images of deep‐water, near‐seafloor geology from 2‐D 4‐C OBC data in the Gulf of MexicoAuthors: Milo M. BackusPaul E. MurrayBob A. HardageRobert J. GraebnerMilo M. BackusBureau of Economic Geology, Jackson School of Geosciences, The University of Texas at AustinSearch for more papers by this author, Paul E. MurrayBureau of Economic Geology, Jackson School of Geosciences, The University of Texas at AustinSearch for more papers by this author, Bob A. HardageBureau of Economic Geology, Jackson School of Geosciences, The University of Texas at AustinSearch for more papers by this author, and Robert J. GraebnerBureau of Economic Geology, Jackson School of Geosciences, The University of Texas at AustinSearch for more papers by this authorhttps://doi.org/10.1190/1.2148319 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract We present a method for constructing high‐resolution converted PS‐wave images of near‐seafloor strata in deep water (∼800m) Gulf of Mexico using data from a 2‐D 4‐C ocean bottom cable (OBC) survey. Images are constructed from radial component common‐ receiver gathers. New concepts presented here include the use of commonreceiver gathers as a proxy for common conversion point gathers in the near‐ocean‐bottom environment, and a method for reducing PP‐wavefield effects on radial gathers to better estimate the upgoing PS‐wavefield. The techniques reduce the effects of P‐wave contamination in the image and allow for better interpretation of near‐oceanbottom sediments. The resulting PS‐images with dominant 90Hz energy are comparable to PP‐images from highresolution data from a 2–8kHz source.Permalink: https://doi.org/10.1190/1.2148319FiguresReferencesRelatedDetailsCited ByCase study: 4D consistent receiver coupling corrections applied to deep‐water ocean bottom cable data31 January 2022 | Geophysical Prospecting, Vol. 70, No. 3References24 May 2016C‐wave spectral broadening by wavelet transformation to match P‐wavelengths: Marcellus shaleJames Gaiser, Richard Verm, and Alvaro Chaveste25 May 2012Extending the high end of C‐wave bandwidth to match P‐wavelengthsJames Gaiser, Richard Verm, and Alvaro Chaveste8 August 2011Integrated 2D 4-C OBC velocity analysis of near-seafloor sediments, Green Canyon, Gulf of MexicoGEOPHYSICS, Vol. 73, No. 6Simultaneous P‐ and S‐wave interval velocity model building of near‐seafloor geology using OBC dataPaul E. Murray and Michael V. DeAngelo15 December 2008 SEG Technical Program Expanded Abstracts 2005ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2005 Pages: 2668 publication data© 2005 Copyright © 2005 Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished: 07 Dec 2005 CITATION INFORMATION Milo M. Backus, Paul E. Murray, Bob A. Hardage, and Robert J. Graebner, (2005), "Enhanced PS‐wave images of deep‐water, near‐seafloor geology from 2‐D 4‐C OBC data in the Gulf of Mexico," SEG Technical Program Expanded Abstracts : 955-958. https://doi.org/10.1190/1.2148319 Plain-Language Summary PDF DownloadLoading ...

Abstract We developed a methodology for manually establishing tie points of depth-equivalent surfaces in P-P and P-S seismic data volumes derived from a 4-C ocean bottom seismic survey using seismic attribute volumes viewed in time slices. These tie points were used as a basis for establishing interpretations of depth-equivalent surfaces throughout the volumes that were then used as a basis for depth registration of several 2-D sections throughout the volume. We examine the Vp/Vs ratios derived from this interpretation. While these ratios are physically reasonable, they are averaged over several stratigraphic sequences and do not provided enough detail to represent the true interval Vp/Vs values of a given sequence. However, we use these Vp/Vs ratios to correct the interpretation and perform an initial registration of the P-S volume to P-P two-way time. An analysis of the registered, or "warped", P-S volume shows the limitations of this simple technique, and from this we infer what processes must be addressed for a robust method of registration. Introduction The work summarized here is part of a larger study undertaken to develop methods of multicomponent data analysis for the detection of gas hydrate prospects in the northern Gulf of Mexico. Methane gas hydrates deposits occur within a narrow window of near ocean-bottom strata extending no more than a few hundred meters below the seafloor, with size and extent dependent on local temperature and pressure conditions in the region. In many regions of North America, including the southern Gulf of Mexico (GOM), Alaska, and the Atlantic and Pacific coasts of the United States, known gas hydrate deposits can be identified on P-wave seismic surveys by a diagnostic bottom-simulating reflector (BSR) at the base of the frozen hydrates. In the northern GOM, gas hydrates do not exhibit the classic BSR. In this region, the known hydrate deposits have no known distinctive seismic signature, but they do tend to be associated with shallow "gas clouds" which show up as no-data or poor-data quality zones on traditional Pwave seismic surveys. Converted-mode shear waves have already been proven a useful tool for imaging through gas cloud regions (Thomsen et. al, 1997) and specifically in the northern GOM for the purpose of identifying deep targets of interest for oil and gas production (Cafarelli et al, 2000, Knapp et al, 2001). We consider the identification of shallow gas clouds for hydrate detection another possible application for this type of multicomponent seismic data. As part of this study, we introduced the use of a set of multicomponent seismic data designed for deep target exploration as a tool to aid in the identification of possible hydrate prospects and other possible engineering hazards in the upper 1000m of strata across a study region. It should be noted that this study area of the northern GOM shelf is not itself a candidate for hydrate deposits. Large regional 3-D multicomponent data sets of such environments in the deepwater GOM are not available to us at this time.

Summary A 9-C 3-D seismic reflection data set from Clark County, Kansas is processed to produce SH and SV data volumes. Data processing is quite straightforward; rotation of the data from field coordinates to radial-transverse coordinates, static corrections (elevation, shot, and receiver) derived from the SH data, NMO correction with a single velocity function, inside-trace mute, and stack. Super gathers monitor the convergence of the shear-wave statics, which are found to be relatively small (+/- 40 ms), and simple to estimate from the dominantly 12 Hz SH data. Single velocity function NMO (velocities derived from SH) show the SV data to be slightly overcorrected, suggesting the presence of vertical transverse isotropy. An inside-trace mute eliminates the surface-wave noise cone. Dominant reflections in the stacked data are from the top and base of the Morrow clastic interval. Reflection signal quality is superior on the SH data.