1887
  1. Home
  2. A-Z Publications
  3. Geophysical Prospecting
  4. Volume 49, Issue 1
  5. Article
Volume 49, Issue 1
  • E-ISSN: 1365-2478

Abstract

Routine amplitude‐versus‐offset or amplitude‐versus‐angle (AVA) analysis is founded on the predicted reflectivity of a planar boundary between isotropic homogeneous half‐spaces, yet many real boundaries of interest to hydrocarbon exploration may violate these assumptions. Here, we evaluate consequences of boundary roughness, i.e. small‐scale, sub‐resolution topography, on the reflecting boundary, to find whether sub‐resolution topography can deceive routine AVA analysis and produce misleading hydrocarbon indicators. We use noise‐free synthetic CMP and stacked‐section seismograms, generated with a Kirchhoff‐integral method, for offsets up to 4000 m. The reflecting boundary was at 2000 m depth below a single overburden layer, and comprised isolated mounds or channels (sinusoidal cross‐section, 5–40 m high and 100–750 m wide), and more complex roughness (simulated with seven 1.5–2 km long bathymetric profiles across modern‐day river‐beds, with dune and bar features up to approximately 20 m or 20 ms TWT vertical relief, and 10–100 m or more lateral extent). Flat‐boundary responses were taken as the ‘reference’ against which to compare waveforms and amplitudes through semblance analysis, AVA intercept and slope cross‐plots, and inferred Poisson's ratios. Physical properties of the media were based on shales and brine‐ or oil‐sands from an offshore UK oilfield.

For the CMP centred on the topographic feature, isolated mounds and channels produced correlated excursions of and from the flat‐boundary response (by approximately 35–200%), simulating the familiar ‘background trend’ but sometimes oblique to it. Inferred Poisson's ratios were around 0.3, but for some channels often fell as low as 0.2, potentially interpretable as gas sand. For complex boundary topographies on a shale/brine‐sand model, AVA parameters were extracted for 29 CMPs, 100 m apart along each of seven profiles. On a cross‐plot, they spanned the flat‐boundary response on a linear trend  = (0.01 ± 0.02) – (1.72 ± 0.09), similar to reported real data and a realistic ‘mudrock trend’ but with outliers both above and below it that could be interpreted as ‘real’ weak anomalies. Poisson's ratios were 0.30 ± 0.01, between the expected values for brine‐ and oil‐sand. This suggests that boundary roughness may contribute to observed trends on cross‐plots and possibly small, but potentially laterally extensive, false AVA anomalies may also be induced.

Loading

Article metrics loading...

/content/journals/10.1046/j.1365-2478.2001.00237.x
2001-12-21
2024-04-25

  • From This Site

    /content/journals/10.1046/j.1365-2478.2001.00237.x
    dcterms_title,dcterms_subject,pub_keyword
    -contentType:Journal -contentType:Contributor -contentType:Concept -contentType:Institution
    10
    5
Loading full text...

Full text loading...

References

  1. AkiK. & RichardsP.G.1980.Quantitative Seismology, Theory and Methods, Vol. 1. W.H. Freeman.
     [Google Scholar]
  2. AllenJ.L. & PeddyC.P.1993.Amplitude Variation with Offset: Gulf Coast Case Studies. Geophysical Development Series 4. Society of Exploration Geophysicists.
     [Google Scholar]
  3. AllenJ.L., PeddyC.P. & FasnachtT.L.1993. Some AVO failures and what (we think) we have learned from them. Leading Edge12, 162–167.
    [Google Scholar]
  4. AshworthP.L., BestJ.L., RodenJ.E., BristowC.S. & KlaassenG.J.2000. Morphological evolution and dynamics of a large, sand‐braid bar, Jamuna River, Bangladesh. Sedimentology47, 533–555 .DOI: 10.1046/j.1365-3091.2000.00305.x
     [Google Scholar]
  5. BakkeN.E. & UrsinB.1998. Thin‐bed AVO effects. Geophysical Prospecting46, 571–587.
    [Google Scholar]
  6. BernéS., DurandJ. & WeberO.1991. Architecture of modern subtidal dunes (sand waves), Bay of Bourgneuf, France. In: The Three‐Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery (eds A.D.Miall and N.Tyler ). Concepts in Sedimentology and Paleontology 3. SEPM (Society for Sedimentary Geology).
     [Google Scholar]
  7. CamboisG.1998. AVO attributes and noise: pitfalls of cross‐plotting. 68th SEG meeting, New Orleans, USA, Expanded Abstracts, 244–247.
  8. CampbellG. & CrottyJ.H.1990. 3D seismic mapping for mine planning purposes at the South Deep prospect. International Deep Mining Conference, SAIMM Symposium Series S102, 569–597.
    [Google Scholar]
  9. CastagnaJ.P.1993. AVO analysis – tutorial and review. In: Offset‐Dependent Reflectivity – Theory and Practice of AVO Analysis (eds J.P.Backus and M.M.Backus ), pp. 3–36. Investigations in Geophysics 8. Society of Exploration Geophysicists.
     [Google Scholar]
  10. CastagnaJ.P. & SmithS.W.1994. Comparison of AVO indicators: a modeling study. Geophysics59, 1849–1855.
    [Google Scholar]
  11. CastagnaJ.P., SwanH.W. & FosterD.J.1998. Framework for AVO gradient and intercept interpretation. Geophysics63, 948–956.
    [Google Scholar]
  12. CowanE.J.1991. The large‐scale architecture of the fluvial Westwater Canyon Member, Morrison Formation (Upper Jurassic), San Juan Basin, New Mexico. In: The Three‐Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery (eds A.D.Miall and N.Tyler ). Concepts in Sedimentology and Paleontology 3. SEPM (Society for Sedimentary Geology).
     [Google Scholar]
  13. EstillR. & WrolstadK.1993. Interpretive aspects of AVO – application to offshore Gulf Coast bright spot analysis. In: Offset‐Dependent Reflectivity – Theory and Practice of AVO Analysis (eds J.P.Backus and M.M.Backus ), pp. 267–284. Investigations in Geophysics 8. Society of Exploration Geophysicists.
     [Google Scholar]
  14. FomelS., BleisteinN., JaramilloH. & CohenJ.K.1996. True amplitude DMO, offset continuation, and AVA/AVO for curved reflectors. 66th SEG Meeting, Denver, USA, Expanded Abstracts, Paper Sl1.6, 1731–1734.
  15. Den Hartog JagerD., GilesM.R. & GriffithsG.R.1993. Evolution of Palaeogene submarine fans of the North Sea, in space and time. In: Proceedings of the 4th Conference on Petroleum Geology of Northwest Europe (ed. J.R.Parker ), pp. 59–71. The Geological Society, London.
  16. HendricksonJ.S.1999.Stacked. Geophysical Prospecting47, 663–705.DOI: 10.1046/j.1365-2478.1999.00150.x
     [Google Scholar]
  17. HeretierF.E., LosselP. & WathneE.1979. Frigg field – large submarine fan trap in Lower Eocene rocks of the Viking Graben, North Sea. In: Giant Oil and Gas Fields of the Decade: 1968–1978. American Association of Petroleum Geologists.
     [Google Scholar]
  18. HermanG.C. & BlonkB.1990. Influence of small‐scale interface roughness in the estimation of lithologic parameters from reflection coefficients. 60th SEG meeting, San Francisco, USA, Expanded Abstracts, 1475–1478.
  19. HustedtB.G. & ClarkR.A.1999. Source/receiver array directivity effects on marine seismic attenuation measurements. Geophysical Prospecting47, 1105–1119.DOI: 10.1046/j.1365-2478.1999.00169.x
     [Google Scholar]
  20. JonesI.F., MandacheV., CampbellS. & LancasterS.1994. 3‐D AVO processing: evolution of a processing sequence. 64th SEG meeting, Los Angeles, USA, Expanded Abstracts, Paper SP6.8, 1615–1618.
  21. KampfmannS.1988. A study of diffraction‐like events on DEKORP2‐S by Kirchhoff theory. Journal of Geophysics62, 163–174.
    [Google Scholar]
  22. LinerC.L. & LinerJ.L.1995. Ground‐penetrating radar: a near‐face experience from Washington County, Arkansas. Leading Edge14, 17–21.
    [Google Scholar]
  23. LoveridgeM.M., ParkesG.E., HattonL. & WorthingtonM.H.1984. Effects of marine airgun source array directivity on seismic data and source signature deconvolution. First Break2, 16–22.
    [Google Scholar]
  24. McGillR.K.1998. Amplitudes of reflecting boundaries, with reference to the Nelson field, UKCS North Sea. PhD thesis, University of Leeds.
  25. MallickS.1998. Determination of the principal directions of azimuthal anisotropy from P‐wave seismic data. Geophysics63, 692–707.
    [Google Scholar]
  26. NeubergJ. & LisapalyL.1997. Kirchhoff synthetics for seismic reflections and diving waves in two dimensions, and application to the D’ layer. Geophysical Journal International129, 587–596.
    [Google Scholar]
  27. NeubergJ. & WahrJ.1991. Detailed investigation of a spot on the core‐mantle boundary using digital PcP data. Physics of the Earth and Planet Interiors68, 132–143.
    [Google Scholar]
  28. OgilvyJ.A.1987. Wave scattering from rough surfaces. Reports of Progress in Physics50, 1553–1608.
    [Google Scholar]
  29. O'MongainA.M. & NeubergJ.W.1996. D’’ topography: fact or fiction? EOS Transactions of the AGU77, 679.
    [Google Scholar]
  30. OstranderW.J.1984. Plane wave reflection coefficients for gas sands at non‐normal angles of incidence. Geophysics49, 1637–1648.
    [Google Scholar]
  31. PaulA. & CampilloM.1988. Diffraction and conversion of elastic waves at a corrugated interface. Geophysics53, 1415–1424.
    [Google Scholar]
  32. ResnickJ.R.1993. Seismic data processing for AVO and AVA analysis. In: Offset‐Dependent Reflectivity – Theory and Practice of AVO Analysis (eds J.P.Backus and M.M.Backus ), pp. 175–189. Investigations in Geophysics 8. Society of Exploration Geophysicists.
     [Google Scholar]
  33. RodenJ.E.1998. The dynamics and sedimentology of megadunes, Jamuna River, Bangladesh. PhD thesis, University of Leeds.
  34. RügerA.1998. Variation of P‐wave reflectivity with offset and azimuth in anisotropic media. Geophysics63, 935–947.
    [Google Scholar]
  35. RutherfordS.R. & WilliamsR.H.1989.Amplitude‐versus‐offset variations in gas sands. Geophysics54, 680–688.
    [Google Scholar]
  36. SayersC.M. & RickettJ.E.1997. Azimuthal variation in AVO response from fractured gas sands. Geophysical Prospecting45, 165–182.
    [Google Scholar]
  37. ScottP. & HelmbergerD.1983. Applications of the Kirchhoff‐Helmholtz integral to problems in seismology. Geophysical Journal of the Royal Astronomical Society72, 237–254.
    [Google Scholar]
  38. ShueyR.T.1985. A simplification of the Zoeppritz equations. Geophysics50, 609–614.
    [Google Scholar]
  39. SimmR., WhiteR. & UdenR.2000. The anatomy of AVO cross‐plots. Leading Edge19, 150–155.
    [Google Scholar]
  40. WaldenA.T.1991. Making AVO sections more robust. Geophysical Prospecting39, 915–942.
    [Google Scholar]
  41. WapenaarK.1999. Amplitude‐variation‐with‐angle behavior of self‐similar interfaces. Geophysics64, 1928–1938.
    [Google Scholar]
  42. WapenaarK., Van WijngaardenA.‐J., Van GelovenW. & Van Der LeijT.1999. Apparent AVA effects of fine layering. Geophysics64, 1939–1948.
    [Google Scholar]
  43. WilliamsonJ.H.1968. Least‐squares fitting of a straight line. Canadian Journal of Physics46, 1845–1847.
    [Google Scholar]
  44. WillsJ.M.1991. The Forties Field, Block 21/10, 22/6a, UK North Sea. In: United Kingdom Oil and Gas Fields, 25 Years Commemorative Series (ed. I.L.Abbots ), pp. 301–318. Geological Society Memoir 14. The Geological Society, London.
  45. ZoeppritzK.1919. Uber reflexion und durchgang seismischer Wellen durch Unstetigkerlsfläschen. Uber Erdbebenwellen VIIB, Nachrichten der Königlichen Gesellschaft der Wissenschaften zu Göttingen, Math. Phys. K1, 57–84.
    [Google Scholar]
http://instance.metastore.ingenta.com/content/journals/10.1046/j.1365-2478.2001.00237.x
Loading
The AVA (amplitude‐versus‐angle) signature of small‐scale reflector topography
Geophysical Prospecting 49, 59 (2001); https://doi.org/10.1046/j.1365-2478.2001.00237.x
/content/journals/10.1046/j.1365-2478.2001.00237.x
/content/journals/10.1046/j.1365-2478.2001.00237.x
Loading

Data & Media loading...

  • Article Type: Research Article

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