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Reverse Time Migration of Prism Waves for Salt Flank Delineation

Reverse Time Migration of Prism Waves for Salt Flank Delineation. Wei Dai, WesternGeco Gerard T. Schuster, King Abdullah University of Science and Technology. Sep 25, 2013. Outline. Introduction and motivation Theory Numerical Results L model Salt model Summary. Introduction.

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Reverse Time Migration of Prism Waves for Salt Flank Delineation

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  1. Reverse Time Migration of Prism Waves for Salt Flank Delineation Wei Dai, WesternGeco Gerard T. Schuster, King Abdullah University of Science and Technology Sep 25, 2013

  2. Outline Introduction and motivation Theory Numerical Results L model Salt model Summary

  3. Introduction • Problem: Vertical boundaries (salt flanks) are difficult to image because they are usually not illuminated by primary reflections. • Solution: Prism waves contain valuable information.

  4. Conventional Method • When the known boundaries are embedded in the velocity model, conventional RTM can migrate prism waves correctly.

  5. Recorded Trace 0 2 Time (s)

  6. Horizontal Reflector Embedded in the Velocity 0 Z (km) 3 Conventional RTM Image 0 Z (km) 3 0 X (km) 6

  7. Reverse Time Migration Formula Source Spectrum Input Data Angular Freq. Green’s functions 0 Z (km) 3

  8. + Ellipses + + Rabbit Ears + + Prism Wave Kernels + Other terms.] 0 Z (km) 3 0 X (km) 6

  9. Migration of Prism Waves Born Modeling 0 Z (km) 3 0 X (km) 6

  10. Migration of Prism Waves 0 Z (km) 3 0 Z (km) 3 0 X (km) 6

  11. Migration of Prism Waves Born Modeling 0 Z (km) 3 0 X (km) 6

  12. Migration of Prism Waves 0 Z (km) 3 0 Z (km) 3 0 X (km) 6

  13. Outline Introduction and motivation Theory Numerical Results L model Salt model Summary

  14. The L Model • Model size: 301 x 601 • Source freq: 20 hz • shots: 32 • geophones: 601 0 Z (km) 3 0 6 X (km)

  15. A Shot Gather of the L Model 0 Time (s) 6.4 0 X (km) 6

  16. Prism Wavepath 0 Z (km) 3 0 Z (km) 3 0 X (km) 6

  17. RTM Image /w Smooth Velocity 0 Z (km) 3 Migration Image of Prism Waves 0 Z (km) 3 0 X (km) 6

  18. The Salt Model • Model size: 601 x 601 0 • Source freq: 20 hz • shots: 601 Z (km) • geophones: 601 6 0 X (km) 6

  19. A Shot Gather of the Salt Model 0 Time (s) 10 0 X (km) 6

  20. RTM with Smooth Velocity Migration Velocity RTM Image 0 Z (km) 6 0 X (km) 6 0 X (km) 6

  21. If the Horizontal Reflectors are embedded in the velocity Migration Velocity RTM Image 0 Z (km) 6 0 X (km) 6 0 X (km) 6

  22. New Method Migration Velocity Conv. RTM Image Prism Wave Image 0 RTM Image 0 Z (km) Z (km) 0 X (km) 6 6 6 0 X (km) 6

  23. New Method Migration Velocity Prism Wave Image 0 Filtered RTM Image 0 Z (km) Z (km) 0 X (km) 6 6 6 0 X (km) 6

  24. Final Image Horizontal RTM Image Final Image 0 Vertical 0 Z (km) Z (km) 0 X (km) 6 6 6 0 X (km) 6

  25. Summary • I propose a new method to migrate prism waves separately. • Avoid the modification of migration velocity. • Reduce cross interference between different waves by migrating different waves in separated steps. Limitations • Computational cost is doubled.

  26. Thanks

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