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WAVEFIELD PREDICTION OF WATER-LAYER-MULTIPLES

WAVEFIELD PREDICTION OF WATER-LAYER-MULTIPLES. Ruiqing He University of Utah Feb. 2004. Outline. Introduction Theory Synthetic experiments Application to Unocal data Conclusion. Introduction. Primary-preserving multiple removal demands

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WAVEFIELD PREDICTION OF WATER-LAYER-MULTIPLES

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  1. WAVEFIELD PREDICTION OF WATER-LAYER-MULTIPLES Ruiqing He University of Utah Feb. 2004

  2. Outline • Introduction • Theory • Synthetic experiments • Application to Unocal data • Conclusion

  3. Introduction • Primary-preserving multiple removal demands • accurate wavefield prediction of multiples. • Other works: • - Delft • - Amundsen, Ikelle, Weglein, etc. • Water layer multiples

  4. Outline • Introduction • Theory • Synthetic experiments • Application to Unocal data • Conclusion

  5. Kirchhoff Summation Forward extrapolate traces down to water bottom Kirchhoff Summation Filtered Subtraction Forward extrapolate bottom traces up to receivers  Emulated Muliples Multiple attenuation Berryhill and Wiggins’s Methods Off-shore seismic data Water surface Receiver line Water bottom

  6. The proposed method Decomposition of receiver-side ghosts Wave forward extrapolation to the water bottom FD Off-shore seismic data FD FD Multiples with last round-trip in water layer Primary- preserving multiple removal Wave forward extrapolation to the receivers DS filtering FD: Finite Difference DS: Direct (simple) Subtraction Other multiple attenuation

  7. Why Finite Difference? • Advantage • - speed • - convenience • - capability: heterogeneous medium • Disadvantage • - dispersion?: reality, high-order FD

  8. Types of Water-Layer-Multiples • LWLM: Multiples that have the last round-trip in the water layer. • Other WLM: other water-layer-multiples except LWLM.

  9. Wavefield Extrapolation of RSG RSG Mirror image of the Receiver line Water surface Receiver line U RSG

  10. RSG f + + U DATA Decomposition of RSG Mirror image of the Receiver line Water surface Receiver line

  11. Outline • Introduction • Theory • Synthetic experiments • Application to Unocal data • Conclusion

  12. Synthetic Model 0 water BSR Depth (m) Salt dome Sandstone 1500 0 3250 Offset (m)

  13. Synthetic seismic data 400 Time (ms) 2500 0 3250 Offset (m)

  14. Decomposed RSG 400 Time (ms) 2500 0 3250 Offset (m)

  15. Predicted LWLM 400 Time (ms) 2500 0 3250 Offset (m)

  16. Waveform Comparisonbetween Data & RSG Data RSG Amplitude 2400 600 Time (ms)

  17. Waveform Comparisonbetween Data & LWLM Data LWLM Amplitude 2400 600 Time (ms)

  18. Waveform Comparisonbetween Data & RSG+LWLM Data RSG + LWLM Amplitude 2400 600 Time (ms)

  19. Elimination of RSG & LWLM 400 Time (ms) 2500 0 3250 Offset (m)

  20. Further Multiple Attenuation 400 Time (ms) 2500 0 3250 Offset (m)

  21. Outline • Introduction • Theory • Synthetic experiments • Application to Unocal data • Conclusion

  22. Unocal field data 600 Time (ms) 2400 0 3175 Offset (m)

  23. Inadequate RSG Decomposition 600 Time (ms) 2400 0 3175 Offset (m)

  24. Emulated LWLM 600 Time (ms) 2400 0 3175 Offset (m)

  25. Waveform comparisonbetween Data & Emulated LWLM Data LWLM Amplitude 1400 Time (ms) 2400

  26. Attenuation of WLM 600 Time (ms) 2400 0 3175 Offset (m)

  27. Attenuation of WLM

  28. Attenuation of WLM 600 Time (ms) 2400 0 3175 Offset (m)

  29. Attenuation of WLM

  30. Subtracted WLM 600 Time (ms) 2400 0 3175 Offset (m)

  31. Outline • Introduction • Theory • Synthetic experiments • Application to Unocal data • Conclusion

  32. Conclusion • Theoretically revives Berryhill and Wiggins • methods for primary-preserving removal of one • kind of water-layer-multiples. • Requirements are practically obtainable, • and can be derived from seismic data. • Applicable to field data with approximations. • Overcomes the Delft method by alleviating • acquisition requirements and the need to know • the source signature.

  33. Future Work • Ghost decomposition for field data. • 3D to 2D seismic data conversion. • Multiple subtraction.

  34. Reference • Berryhill J.R. and Kim Y.C., 1986, Deep-water pegleg and • multiples: emulation and suppression: Geophysics Vol. 51, • 2177-2184. • Wang Y., 1998, Comparison of multiple attenuation methods • with least-squares migration filtering: UTAM 1998 annual • report, 311-342. • Wiggins J.W., 1988, Attenuation of complex water-multiples • by wave-equation-based prediction and subtraction: • Geophysics Vol.53 No.12, 1527-1539.

  35. Thanks • 2003 members of UTAM for financial support.

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