Topographic Phase Shift with Applications to Migration and Multiple Prediction

1. Topographic Phase Shift with Applications to Migration and Multiple Prediction Ruiqing He University of Utah Feb. 2005

2. Outline Wavefield extrapolation. Topographic phase-shift method. Application to migration. Application to multiple prediction. Summary.

3. Outline Wavefield extrapolation. Topographic phase-shift method. Application to migration Application to multiple prediction. Summary.

4. Wavefield Extrapolation One-way wave-equation. - Phase-shift method (Gazdag, 1984). Iterative (depth-by-depth) implementation. Horizontal velocity variation: - PSPI, Split-step, Fourier-FD, etc. Irregular surfaces.

5. Reshef’s Approach for Topography Geophone line Datum lines

6. Issues with Reshef’s Approach Non-uniform geophone spacing problem

7. Outline Wavefield extrapolation. Topographic phase-shift method. Application to migration. Application to multiple prediction. Summary.

8. Topographic Phase-shift Method z = 0 z = Z(x)

9. Synthetic Test z = 0 z = Z(x)

10. A Part of SMAART DATA

11. Extrapolation to Water Bottom

12. Reconstruction

13. Waveform Comparison

14. Outline Wavefield extrapolation. Topographic phase-shift method. Application to migration. Application to multiple prediction. Summary.

15. Mapleton Land Seismic Data

16. Acquisition Geometry 20 m 78 m

17. Topographic Phase-shift Migration F2 F3 F4 F5 f6

18. Waveform Tomography (Sheng and Buddensiek, 2004)

19. Outline Wavefield extrapolation. Topographic phase-shift method. Application to migration. Application to multiple prediction. Summary.

20. Water-layer Multiple (WLM) Major free-surface multiples in marine data. Can be very precisely predicted. Very few acquisition requirements. (even in a single shot gather).

21. Finite-difference Experiments • Unpredictable WLM resemble their predictable counterparts. Only one type WLM can be predicted. • Improvement can be made by using the receiver-side ghost rather than the data in the prediction.

22. Unocal Data COG (177m)

23. Predicted WLM

24. Waveform Comparison At a geophone above non-flat water bottom At a geophone above flat water bottom

25. WLM Attenuation

26. A Shot Gather

27. WLM Prediction in The Shot Gather

28. WLM Suppression in Shot Gather

29. A NMO Panel

30. A NMO Panelafter Demultiple

31. Stack before Demultiple Time (S) Offset (m)

32. Stack after Demultiple Time (S) Offset (m)

33. Poststack Migration before Demultiple

34. Poststack Migration after Demultiple

35. 3D Synthetic Experiment 128 11 dy= 50 m dx= 25 m Sea Floor Reflector

36. 3D Synthetic Data

37. WLM Prediction

38. WLM Suppression

39. Outline Wavefield extrapolation. Topographic phase-shift method. Application to migration Application to multiple prediction. Summary.

40. Summary Topographic phase shift is efficient for wavefield extrapolation from irregular surfaces. It is useful for migration and multiple prediction, especially for large and 3D data sets.