1887
Volume 66, Issue 5
  • E-ISSN: 1365-2478

Abstract

ABSTRACT

In many cases, the seismic response of bottom‐simulating reflectors is characterised by low frequencies called “low‐frequency shadow”. Generally, this phenomenon is interpreted as attenuation due to partial saturation with free gas. Actually, this frequency loss may have multiple causes, with a normal moveout stretch as a possible candidate. To analyse this phenomenon, we compute synthetic seismograms by assuming a lossy bottom‐simulating layer, with varying quality factor and thickness, bounded by the upper hydrate‐brine/gas‐brine and lower gas‐brine/brine interfaces. First, we estimate the shift of the centroid frequency of the power spectrum as a function of the travelled distance of the seismic pulse. Then, we perform one‐dimensional numerical experiments to quantify the loss of frequency of the seismic event below the bottom‐simulating reflector as a function of the quality factor of the bottom‐simulating layer and its thickness (due to wave interference). Then, we compute shot gathers to obtain the stacked section, with and without the normal moveout stretch correction and with and without the presence of wave attenuation in the bottom‐simulating layer. The results indicate that the low‐frequency shadow due to the normal moveout stretch is stronger than that due to attenuation and may constitute a false indicator of the presence of gas. In fact, often, the low‐frequency shadow overlies events with higher frequencies, in contradiction with the physics of wave propagation. This is particularly evident when the low‐frequency shadow is so extensive that the presence of high frequencies below cannot be justified by the acquisition geometry.

Loading

Article metrics loading...

/content/journals/10.1111/1365-2478.12623
2018-03-25
2024-04-26
Loading full text...

Full text loading...

References

  1. BarnesA.E.2013. The myth of low‐frequency shadows. EAGE Workshop on Seismic Attenuation.
  2. BrieA., PampuriF., MarsalaA.F. and MeazzaO.1995. Shear sonic interpretation in gas‐bearing sands. SPE Annual Technical Conference, 30595, 701–710.
    [Google Scholar]
  3. CanningA. and MalkinA.2008. Removing NMO/migration stretch effects for improved AVO analysis. Proceedings of Hyderabad 2008.
  4. CarcioneJ.M.2014. Wave Fields in Real Media. Theory and Numerical Simulation of Wave Propagation in Anisotropic, Anelastic, Porous and Electromagnetic Media, 3rd edn, Elsevier.
    [Google Scholar]
  5. CarcioneJ.M. and GeiD.2004. Gas hydrate concentration estimated from P‐ and S‐wave velocities at the Mallik 2L‐38 research well, Mackenzie Delta, Canada. Journal of Applied Geophysics56, 73–78.
    [Google Scholar]
  6. CarcioneJ.M., GeiD., RossiG. and MadrussaniG.2005a. Estimation of gas hydrate concentration and free‐gas saturation at the Norwegian‐Svalbard continental margin. Geophysical Prospecting53, 803–810.
    [Google Scholar]
  7. CarcioneJ.M., GeiD., PicottiS. and MicheliniA.2012. Cross‐hole electromagnetic and seismic modeling for CO2 detection and monitoring in a saline aquifer. Journal of Petroleum Science and Engineering100, 162–172.
    [Google Scholar]
  8. CarcioneJ.M., GeiD. and TreitelS.2010. The velocity of energy through a dissipative medium. Geophysics75, T37–T47.
    [Google Scholar]
  9. CarcioneJ.M., HelleH.B., SantosJ.E. and RavazzoliC.L.2005b. A constitutive equations and generalized Gassmann modulus for multi‐mineral porous media. Geophysics70, N17–N26.
    [Google Scholar]
  10. CarcioneJ.M. and PicottiS.2006. P‐wave seismic attenuation by slow‐wave diffusion. Effects of inhomogeneous rock properties. Geophysics71, O1–O8.
    [Google Scholar]
  11. CarcioneJ.M. and TinivellaU.2000. Bottom simulating reflectors: seismic velocities and AVO effects. Geophysics65, 54–67. Errata: 2001, 66, 984.
    [Google Scholar]
  12. CastagnaJ.P., SunS.J. and SiegfriedR.W.2003. Instantaneous spectral analysis: detection of low‐frequency shadows associated with hydrocarbons. The Leading Edge22(2), 120–127.
    [Google Scholar]
  13. DelBen A., ForteE., GelettiR., MocnikK. and PipanM.2011. Seismic exploration of a possible gas‐reservoir in the south Apulia foreland. Bolletino di Geofisica Teorica ed Applicata52, 607–623.
    [Google Scholar]
  14. DewanganP., MandalR., JaiswalP., RamprasadT. and SriramG.2014. Estimation of seismic attenuation of gas hydrate bearing sediments from multi‐channel seismic data: a case study from Krishna‐Godavari offshore basin. Marine and Petroleum Geology58, 356–367.
    [Google Scholar]
  15. DunkinJ.W. and LevinF.K.1973. Effects of normal moveout on a seismic pulse. Geophysics38, 635–642.
    [Google Scholar]
  16. EbromD.2004. The low‐frequency gas shadow on seismic sections. The Leading Edge23(8), 772.
    [Google Scholar]
  17. GeiD. and CarcioneJ.M.2003. Acoustic properties of sediments saturated with gas hydrate, free gas and water. Geophysical Prospecting51(2), 141–158.
    [Google Scholar]
  18. GelettiR. and BusettiM.2011. A double bottom simulating reflector in the western Ross Sea (Antarctica). Journal of Geophysical Research116, B04101.
    [Google Scholar]
  19. MavkoG., MukerjiT. and DvorkinJ.1998. The Rock Physics Handbook: Tools for Seismic Analysis in Porous Media. Cambridge, UK: Cambridge University Press.
    [Google Scholar]
  20. MüllerT., GurevichB. and LebedevM.2010. Seismic wave attenuation and dispersion resulting from wave‐induced flow in porous rocks—A review. Geophysics75, A147–A164.
    [Google Scholar]
  21. PerroudH. and TygelM.2004. Nonstretch NMO. Geophysics69, 599–607.
    [Google Scholar]
  22. QadrouhA.N., CarcioneJ.M., BotelhoM.A.B., HarithZ.Z.T. and SalimA.M.2014. On optimal NMO and generalised Dix equations for velocity determination and depth conversion. Journal of Applied Geophysics101, 136–141.
    [Google Scholar]
  23. RossiG., GeiD., BöhmG., MadrussaniG. and CarcioneJ.M.2007. Attenuation tomography: an application to gas‐hydrate and free‐gas detection. Geophysical Prospecting55, 655–669.
    [Google Scholar]
  24. SainK., SinghA.K., ThakurN.K. and KhannaR.2009. Seismic quality factor observations for gas‐hydrate‐bearing sediments on the western margin of India. Marine Geophysical Researches30, 137–145.
    [Google Scholar]
  25. TaylorM.H., DillonW.P. and PecherI.A.2000. Trapping and migration of methane associated with the gas hydrate stability zone at the Blake Ridge Diapir: new insights from seismic data. Marine Geology164, 79–89.
    [Google Scholar]
  26. TorrenceC. and CompoG.P.1998. A practical guide to wavelet analysis. Bulletin of American Meteorological Society79, 61–78.
    [Google Scholar]
  27. VannesteM., De BatistM., GolmshtokA., KremlevA. and VersteegW.2001. Multi‐frequency seismic study of gas hydrate‐bearing sediments in Lake Baikal, Siberia. Marine Geology172, 1–21.
    [Google Scholar]
  28. WangL., GaoJ., XuaZ., WengB. and JiangX.2014. Hydrocarbon detection using adaptively selected spectrum attenuation. Journal of Applied Geophysics105, 59–66.
    [Google Scholar]
  29. WhiteJ.E.1975. Computed seismic speeds and attenuation in rocks with partial gas saturation. Geophysics40, 224–232.
    [Google Scholar]
  30. WyllieM.R.J., GregoryA.R. and GardnerL.W.1956. Elastic wave velocities in heterogeneous and porous media. Geophysics21, 41–70.
    [Google Scholar]
http://instance.metastore.ingenta.com/content/journals/10.1111/1365-2478.12623
Loading
/content/journals/10.1111/1365-2478.12623
Loading

Data & Media loading...

  • Article Type: Research Article
Keyword(s): Attenuation; BSR; low‐frequency shadow; NMO stretch

Most Cited This Month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error