1. Adaptive Grid Reverse-Time Migration Yue Wang

2. Outline Motivation and ObjectiveMotivation and Objective Reverse Time MethodologyReverse Time Methodology Salt Dome Model TestSalt Dome Model Test Field Data TestField Data Test ConclusionsConclusions

3. Problem Kirchhoff migration is not optimal for complex velocity model.Kirchhoff migration is not optimal for complex velocity model.

4. Marmousi Model Distance (km) Depth (km) 3 0 09 Low-velocity wedge

5. Problem Using first arrival time Difficulty in imaging Kirchhoff migration

6. Problem Reverse-Time Migration RTM) Image complex structure Expensive Using multi-arrival time

7. Solution Fast RTM Variable grid size Variable time step

8. Objective Develop fast reverse time migration for land and marine multi-component dataDevelop fast reverse time migration for land and marine multi-component data

9. Outline Motivation and ObjectiveMotivation and Objective Reverse Time MethodologyReverse Time Methodology Salt Dome Model TestSalt Dome Model Test Field Data TestField Data Test ConclusionsConclusions 

10. Reverse Time Operator Elastic wave equation A 2-4 staggered-grid FD solver

11. Variable Grid Size Distance Depth Low velocity High velocity

12. Variable Grid Size Fine grid (dx dz) Coarse grid (3dx 3dz) z

13. Variable Grid Size Use wave equation to propagate waves Fine grid Coarse grid

14. Variable Time Step coarse grid, fine time step coarse grid, coarse time step Distance Depth

15. Variable Time Step z dt t dt 3 dt dt

16. Variable Time Step z Fine time step Coarse time step t Use wave equation to propagate waves

17. Variable Time Step Falk et al. (1998, Geophys. Pros. ): 1. Non-staggered-grid FD 1. Non-staggered-grid FD 2. 2x time step change 2. 2x time step change

18. Variable Time Step The new method : 1. Staggered-grid FD 1. Staggered-grid FD 2. 3x time step change 2. 3x time step change

19. Numerical Results Fine time step Time t1 Amplitude Coarse time step Depth Depth Time t2 Amplitude No artificial reflections

20. Outline Motivation and ObjectiveMotivation and Objective Reverse Time MethodologyReverse Time Methodology Salt Dome Model TestSalt Dome Model Test Field Data TestField Data Test ConclusionsConclusions 

21. Salt Model Distance (km) Depth (km) 2.7 0 04.5

22. Velocity Profile Velocity (km/s) Depth (km) Velocity (km/s) 1.5402 2.7 0 Depth (km) 2.7 0 PS

23. Velocity Profile Velocity (km/s) Depth (km) Velocity (km/s) 1.5402 2.7 0 PS Fine grid size Fine time step Coarse grid size Coarse time step

24. Shot Gather Normal Stress VerticalHorizontal Time (s) Distance (km) 2 0 0.93.6 0.93.6 0.93.6

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. Reverse Time Migration Distance (km) Depth (km) 2.5 0 0.454.05

28. Distance (km) Depth (km) 2.5 0 0.454.05 Reverse Time Migration

29. Outline Motivation and ObjectiveMotivation and Objective Reverse Time MethodologyReverse Time Methodology Salt Dome Model TestSalt Dome Model Test Field Data TestField Data Test ConclusionsConclusions 

30. Processed CSG 2.7 0 Radial Component Vertical Component Time (s) Trace Number 080080

31. Common Offset Gather ( Vertical Component) Distance (km) Depth (km) 4 0 027 Signal/Noise Ratio High

32. Common Offset Gather ( Radial Component) Distance (km) Depth (km) 4 0 027 Signal/Noise Ratio Low

33. Kirchhoff Migration ( Vertical Component) Distance (km) Depth (km) 4 0 027

34. Kirchhoff Migration ( Radial Component) Distance (km) Depth (km) 4 0 027

35. RTM Distance (km) Depth (km) 4 0 027

36. Comparison Distance (km) Depth (km) 4 0 027 Distance (km) 027 RTMKM

37. Outline Motivation and ObjectiveMotivation and Objective Reverse Time MethodologyReverse Time Methodology Salt Dome Model TestSalt Dome Model Test Field Data TestField Data Test Conclusions and Future WorkConclusions and Future Work 

38. Conclusions 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 Use primary and multiple reflections for imagingUse primary and multiple reflections for imaging

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

40. Raw CSG Time (s) 2.7 0 Radial Component Vertical Component 080080 Trace Number

41. Main Processing Flow Geometry assignment, datuming and so on Trace editing Surface wave attenuation, amplitude balancing P-velocity analysis S-velocity analysis Relative gain compensation, surface velocity estimation KM RTM

42. Shallow Velocity Distance (km) Depth (km) 0.4 0 027

43. Future Work Apply the RTM scheme for data set with more complex structures.Apply the RTM scheme for data set with more complex structures.