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LEAST SQUARES WAVEPATH MIGRATION

LEAST SQUARES WAVEPATH MIGRATION. Y. Liu and H. Sun. Geology and Geophysics Department University of Utah. Outline. . Objective . Wavepath Migration . Least Squares Wavepath Migration . Numerical Results . Field Data Results . Conclusions. Objective. Least-Squares Migration

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LEAST SQUARES WAVEPATH MIGRATION

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  1. LEAST SQUARES WAVEPATH MIGRATION Y. Liu and H. Sun Geology and Geophysics Department University of Utah

  2. Outline . Objective . Wavepath Migration . Least Squares Wavepath Migration . Numerical Results . Field Data Results . Conclusions

  3. Objective • Least-Squares Migration • a. Advantages: • Apply to Incomplete data • Reduce acquisition footprint • Improve Image resolution • b. Disadvantage: • Need more calculation time

  4. Objective Least Squares Migration: • Forward Modeling: fast • Migration: slow

  5. Objective Wavepath Migration: Advantages: • Save calculation time • Suppress artifacts

  6. Objective Least-Squares Wavepath Migration: • Advantages: • Apply to Incomplete data • Reduce acquisition footprint • Improve resolution • Save calculation time

  7. Outline . Objective . Wavepath Migration . Least Squares Wavepath Migration . Numerical Results . Field Data Results . Conclusions

  8. Fat Ray Wavepath Migration ( Xg, 0 ) Fat Ellipsoid KM : Fat Ellipsoid, 3-D CPU WM: Hatched Area, 1.5-D CPU

  9. Traveltime + Ray Direction True Reflection point Small Migration Aperture Fewer Artifacts Less Expensive

  10. KM Image (CPU: 1.0) WM Image (CPU: 0.78) SEG Overthrust Model Results 0 Offset (km) 18 0 Offset (km) 18 0 0 B B Depth (km) Depth (km) A A 4 4

  11. CPU Comparison in 3-D SEG/EAGE Salt Data KM: 1 WM: 1/33 West Texas Field Data KM: 1 WM: 1/14

  12. Outline . Objective . Wavepath Migration . Least Squares Wavepath Migration . Numerical Results . Field Data Results . Conclusions

  13. Least Square Wavepath Migration Forward : d=Lm (1) Migration: mst=L d (2) Objective Function: P(m)=|| Lm-d ||(3) LSWM: mst=[LL] Ld (4) T 2 0 T -1 T

  14. Least Square Wavepath Migration Iteration process: Field Data Wavepath Migration Forward Synthetic Data Stop Criteria Y/N Wavepath Migration

  15. Outline . Objective . Wavepath Migration . Least Squares Wavepath Migration . Numerical Results . Field Data Results . Conclusions

  16. Depth (m) X (km) 0 4 Point Scatterer model X(km) 0 4 0 0 . Time (s) Depth(km) 2.5 4

  17. . Scatterer Image X (km) X (km) X (km) 0 4 0 4 0 4 0 Depth(km) 4 KM image WM image LSWM image

  18. Outline . Objective . Wavepath Migration . Least Squares Wavepath Migration . Numerical Results . Field Data Results . Conclusions

  19. CSG for Mobil Data Trace 1 120 0 GEOMETRY Shots: 668 Trace: 120 Total: 80160 Ns=1500 Dt=4ms Ds=25m Dg=25m Min/Offset=262m Time(s) 5

  20. Velocity Model CDP Number 0 19.9 0 3.5 Dx=12.5 Dz=12.5 Nx=1594 Nz=281 CDP=12.5 (Km/s) Depth (km) 1.5 3.5

  21. WM vs. LSWM X(Km) X(Km) 4.8 19.0 19.0 Depth(Km) 3.4 After 15 iternations

  22. WM Image for Mobil Data 12.0 X(m) 18.0 Depth(m) 2.8 WM image (0) 18.0 12.0 Depth(m) 2.8 LSWM image (15)

  23. Outline . Objective . Wavepath Migration . Least Squares Wavepath Migration . Numerical Results . Field Data Results . Conclusions

  24. Conclusions • Suppress artifacts • Improve Resolution • Computation time (Mobil Data) • WM CPU 1.0 • LSWM CPU (15): 8.5 • Slightly sensitive to velocity

  25. Acknowledgements We thank 2001 UTAM sponsors for their financial supports

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