1. Reverse-Time Migration By A Variable Grid-Size And Time-Step Method Yue Wang University of Utah

2. Outline BackgroundBackground Motivation & ObjectiveMotivation & Objective MethodologyMethodology Numerical ExamplesNumerical Examples ConclusionsConclusions

3. Forward Modeling Distance (km) Depth (km) 1 0 04.5 *  obs Source Geophone Line

4. Reverse Time Migration Distance (km) Depth (km) 1 0 04.5  obs Extrapolated Wavefield  obs Reversed traces

5. Reverse-Time Migration Extrapolated Wavefield Imaging Condition Migration Section

6. Outline BackgroundBackground Motivation & ObjectiveMotivation & Objective MethodologyMethodology Numerical ExamplesNumerical Examples ConclusionsConclusions

7. Ocean-Bottom Survey Distance (km) Depth (km) 1 0 04.5 * Source Geophone Line

8. Problem Distance (km) Depth (km) 1 0 04.5 * Receiver-side Multiples

9. Synthetic Shot Gather Time (s) Distance (km) Receiver side multiples 2 0 0.93.6

10. Field Data Time (s) Distance (m) 4 0 -80 1900 Receiver side multiples

11. Time Migration Time (s) Distance (m) 4 0 -80 1900 Receiver side multiples

12. Objective Using both primary and receiver side multiple reflections for imaging by reverse-time migration.Using both primary and receiver side multiple reflections for imaging by reverse-time migration. Fast Reverse-Time MigrationFast Reverse-Time Migration Elastic RT Migration for Land & Ocean Bottom Multicomponent DataElastic RT Migration for Land & Ocean Bottom Multicomponent Data

13. Outline BackgroundBackground Motivation & ObjectiveMotivation & Objective MethodologyMethodology Numerical ExamplesNumerical Examples ConclusionsConclusions

14. Ocean-Bottom Survey Distance (km) Depth (km) 1 0 0 *PVUp-going Multi-Component Data

15. Two RTM Schemes Migrate particle velocity onlyMigrate particle velocity only (conventional scheme) Migrate pressure and particle velocity simultaneouslyMigrate pressure and particle velocity simultaneously

16. Key Idea Primary + Multiple Correct Positions P & V Scheme

17. Distance Depth Correct Position Down-going waves Reversed Traces PV

18. Key Idea Primary + Multiple Incorrect Positions V-Only Scheme

19. Particle Velocity Only Scheme Distance Depth Incorrect Reversed Traces V

20. Variable Grid-Size and Time-Step coarse grid, fine time step coarse grid, coarse time step Distance Depth fine grid, fine time step

21. Outline BackgroundBackground Motivation & ObjectiveMotivation & Objective MethodologyMethodology Numerical ExamplesNumerical Examples ConclusionsConclusions

22. Synthetic Marine DataSynthetic Marine Data * 2D Elastic Salt Model * 2D Elastic Salt Model * 3D Acoustic SEG/EAGE Model * 3D Acoustic SEG/EAGE Model 2D Land Data2D Land Data Numerical Results

23. 2-D Salt Model Distance (km) Depth (km) 2.7 0 04.5

24. Shot Gather PressureVerticalHorizontal Time (s) Distance (km) 2 0 0.93.6 0.93.6 0.93.6 PS PP

25. Kirchhoff Migration Distance (km) Depth (km) 2.5 0 0.454.05

26. Kirchhoff Migration Distance (km) Depth (km) 2.5 0 0.454.05

27. Distance (km) Depth (km) 2.5 0 0.454.05 Particle-Velocity RT Scheme

28. Distance (km) Depth (km) 2.5 0 0.454.05 P & V RT Scheme

29. Kirchhoff Migration Distance (km) Depth (km) 2.5 0 0.454.05

30. Synthetic Marine DataSynthetic Marine Data * 2D Elastic Salt Model * 2D Elastic Salt Model * 3D Acoustic SEG/EAGE Model * 3D Acoustic SEG/EAGE Model 2D Land Data2D Land Data Numerical Results

31. 3-D SEG/EAGE Salt Model Distance (km) Depth (km) 2 0 04.5 Ocean-Bottom Geophone Line Exploding Reflector Source

32. Particle-Velocity RT Scheme Distance (km) Depth (km) 2 0 04.5

33. Particle-Velocity RT Scheme Distance (km) Depth (km) 2 0 04.5

34. Distance (km) Depth (km) 2 0 04.5 P & V RT Scheme

35. Distance (km) Depth (km) 2 0 04.5 P & V Scheme

36. Particle-Velocity RT Scheme Distance (km) Depth (km) 2 0 04.5

37. Distance (km) Depth (km) 2 0 04.5 P & V RT Scheme

38. Synthetic Marine DataSynthetic Marine Data * 2D Elastic Salt Model * 2D Elastic Salt Model * 3D Acoustic SEG/EAGE Model * 3D Acoustic SEG/EAGE Model 2D Land Data2D Land Data Numerical Results

39. East Texas Land Data 2.7 0 Radial Component Vertical Component Time (s) Trace Number 080080 Weak Signal/Noise Ratio

40. Reverse-Time Migration Distance (km) Depth (km) 4 0 027 Distance (km) 027 Kirchhoff Migration (Vertical Component)

41. Conclusions Uses primary and multiple reflections for imagingUses primary and multiple reflections for imaging Variable RTM 10 times faster than standard RTMVariable RTM 10 times faster than standard RTM Migrates land and marine multi-component dataMigrates land and marine multi-component data

42. Acknowledgement We are grateful to the 1999 sponsors of the UTAM consortium for the financial support

43. Questions Please contact Yue Wang at: ywang@mines.utah.edu