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P- and S- wave velocities of consolidated sediments from a seafloor seismic survey in the North Celtic Sea Basin, offshore Ireland

By Donna J. Shillington, Timothy A. Minshull, Christine Peirce and John M. O'Sullivan


A geophysical survey was conducted over a hydrocarbon prospect in the North Celtic Sea Basin using a small array of ocean-bottom seismographs (OBSs). The purpose of this study was to determine the ratio of (P) compressional- to (S) shear-wave velocity of consolidated sedimentary rocks in order to constrain possible subsurface variations in pore-fluid content. The ratio of VP and VS- is known to be particularly sensitive to lithology, porosity and pore-fluid content, making it a useful parameter for evaluating hydrocarbon prospects. OBSs offer a relatively cheap and time-effective means of acquiring multi-component data compared with ocean-bottom cables. In this contribution, we demonstrate the ability of an OBS survey comprising three pairs of two OBSs spaced at 1.6 km to recover lateral variations in the VP/VS ratio. A key requirement of this type of study is that S-waves will be generated by mode conversions in the subsurface, since they cannot be generated in nor travel through fluids. In this survey, the contrast in physical properties of the hard seabed of the North Celtic Sea Basin provided a means of generating converted S-waves. Two-dimensional ray-tracing and forward modeling was used to create both VP and VS models along a profile crossing the Blackrock prospect in the North Celtic Sea Basin. These models comprise four layers and extend to a maximum depth of 1.1 km. The observed northward decrease in the VP/VS ratio at depths of 500-1000 m below the seafloor in the study area is interpreted to represent lateral variation in the amount of gas present in the pore space of Upper Cretaceous chalks and shales overlying the prospective reservoir

Topics: QE
Year: 2008
OAI identifier:
Provided by: e-Prints Soton

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  3. (2005). Advances in seismic imaging through basalts: A case study from the Faroe-Shetland Basin: Petroleum Geoscience, doi
  4. (1998). An assessment of Irish offshore basins and petroleum plays: doi
  5. (1991). Chalk porosity and Tertiary uplift, Western Approaches Trough, doi
  6. (2002). Combined interpretation of PP and PS data provides direct access to elastic rock properties: Leading Edge, doi
  7. (1998). Exploration in the Shetland-Faeroe Basin using densely spaced arrays of ocean-bottom seismometers: doi
  8. (1976). Fluid saturation effects on dynamic elastic properties of sedimentary rocks: doi
  9. (2002). Imaging through gas clouds; case histories from the Gulf of Mexico: Annual Meeting Expanded Abstracts - AAPG, doi
  10. (1999). Modelling strategies and model assessment for wide-angle seismic traveltime studies: doi
  11. (2002). Pre-stack inversion of a Gulf of Thailand OBC data set: doi
  12. (2007). Radiocarbon constraints on the age of the maximum advance of the British-Irish Ice Sheet in the Celtic Sea: Quaternary Science Reviews, doi
  13. (1992). Seismic traveltime inversion for 2-D crustal velocity structure: doi
  14. (1985). Shear waves and lithology,
  15. (2000). Shear-wave velocity and density estimation from PS-wave AVO analysis: Application to an OBS dataset from the North Sea: Geophysics, doi
  16. (1978). Sound velocity-density relations in sea-floor sediments and rocks: doi
  17. (1995). Tectono-stratigraphy of the North Celtic Sea Basin, doi
  18. (1995). Tertiary uplift and inversion history in the North Celtic Sea Basin and its influence on source rock maturity, doi
  19. (1995). The definition of the Albian 'A' Sand reservoir fairway and aspects of associated gas accumulations in the North Celtic Sea Basin, doi
  20. (1998). Three-dimensional seismic refraction tomography: A comparison of two methods applied to data from the Faroe Basin: doi
  21. (1979). Vp/Vs and Poisson's ratios in marine sediments and rocks: doi
  22. (2003). Vp/Vs ratio along the Vøring Margin, NE Atlantic, derived from OBS data: implications on lithology and stress field: Tectonophysics, doi

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