Wave-Equation Interferometric Migration of VSP Data

1. Wave-Equation Interferometric Migration of VSP Data Ruiqing He Dept. of Geology & Geophysics University of Utah

2. Outline • Acknowledgements • Introduction of Seismic Interferometry • Wave-equation Interferometric Migration • 3D Migration of VSP Multiples • Salt Flank Imaging • Conclusion & Technical Contributions

3. Outline • Acknowledgements • Introduction of Seismic Interferometry • Wave-equation Interferometric Migration • 3D Migration of VSP Multiples • Salt Flank Imaging • Conclusion & Technical Contributions

4. Acknowledgements • Thank Jerry Schuster for enlightening lectures, innovating discussions, supervising and support. • Thank Bob Smith, Cari Johnson, Kris Sikorski for teaching and supervising. Thank Yue Wang for supervising. • Thank my family.

5. Outline • Acknowledgements • Introduction of Seismic Interferometry • Wave-equation Interferometric Migration • 3D Migration of VSP Multiples • Salt Flank Imaging • Conclusion & Technical Contributions

6. Introduction of Seismic Interfeometry • Passive Seismic Imaging: • Claerbout (1968) • Katz (1990); Cole (1995) • Daneshvar et al. (1995)

7. Introduction of Seismic Interfeometry (continued) • Daylight Imaging: • Rickett & Claerbout (1996, 1999, 2000) • Helioseismologists (Duvall et al., 1993) • Schuster (1999,2000), Wapenaar (2003)

8. Introduction of Seismic Interfeometry (continued) • Virtual Source: • Calvert, Bakulin, et al. (2004) Overburden Target

9. Introduction of Seismic Interfeometry (continued) • Seismic Interferometry: • Schuster & Rickett (1999) • Schuster (2001) • Yu & Schuster (2001, 2006) • Jiang et al. (2005) • No restriction on source distribution • Arbitrary velocity model • Many types of events used

10. Introduction of Seismic Interfeometry (continued) • Seismic Interferometry Theory:

11. Introduction of Seismic Interfeometry (continued) • Migration of VSP Multiples:

12. 3D Introduction of Seismic Interfeometry (continued) • Successful Applications: Xiao, et al. (2005) UTAM report Drilling …

13. Introduction of Seismic Interfeometry (continued) • Robust Imaging: Kirchhoff Migration KM Overburden IM Interferometric Migration

14. Introduction of Seismic Interfeometry (continued) • Super Resolution: Kirchhoff Migration Interferometric Migration

15. Introduction of Seismic Interfeometry (continued) CDP multiple migration Various applications: VSP multiple migration overburden HSP imaging Salt Dome VSP salt flank imaging

16. Outline • Acknowledgements • Introduction of Seismic Interferometry • Wave-equation Interferometric Migration • 3D Migration of VSP Multiples • Salt Flank Imaging • Conclusion & Technical Contributions

17. Wave-Equation Interferometric Migration (WEIM): consideration IVSP • Kirchhoff Migration Costs: • Crosscorrelation • Ray tracing • Storage for traveltime tables • For Example: • To obtain 85 x 87 x 1400 migration • cube, ~300 GB disk is required.

18. WEIM: theory IVSP • WEIM costs for one gather: • One wavefield extrapolation • One ray tracing • One traveltime table

19. The picked time is imposed as an initial condition in ray tracing. It is as efficient as conventional point-source ray tracing. Ray Tracing Unknown medium Known medium

20. 3D WEIM of VSP Multiples

21. 2D Synthetic Test Synthetic model Synthetic data 600 shots 0 0 Time (s) 12 geophpnes Depth (m) Multiples 5 4000 0 Offset (m) 0 6000 Offset (m) 6000

22. Migration Comparison Migration of primaries Migration of multiples 0 0 Depth (m) Depth (m) 4000 4000 0 Offset (m) 0 6000 Offset (m) 6000

23. Field Data Application

24. Survey Geometry ~ 11 km ~ 11 km 3 similar spirals, each corresponding to an offset-ed geophone group. Each geophone group has 12 geophones. ~ 5 km deep

25. 3D WEIM Result Migration of only one receiver gather

26. Slice Movie Migration of only one receiver gather

27. Slice of 3D Migration Cube 0 Depth (m) 6500 Offset (m) 11000 0

28. Common Image Gather 0 Depth (m) 6500 1 Offset (m) 36

29. 120 shots ? 98 geophones VSP Salt Flank Imaging Overburden

30. Interferometric Migration Result

31. A Synthetic Experiment 10 shots Overburden 94 geophones

32. A Shot Gather

33. WEIM Result (one shot) 2700 Depth (m) Artifacts 5500 0 1700 Offset (m)

34. WEIM Result (ten shots) 2700 Depth (m) 5500 0 1700 Offset (m)

35. Outline • Acknowledgements • Introduction of Seismic Interferometry • Wave-equation Interferometric Migration • 3D Migration of VSP Multiples • Salt Flank Imaging • Conclusion & Technical Contributions

36. Conclusion • Seismic interferometry is a robust imaging tool, and has a variety of applications. • However, the relatively weak energy waves and low fold imaging in some applications could result in the low S/N ratio of the image.

37. Technical Contributions (I) • Wave-equation interferometric migration is proposed for efficient 3D migration of VSP multiples. • It is as robust to velocity estimation errors as surface seismic imaging. • It is much more cost efficient than surface seismic surveys in obtaining a 3D subsurface image volume. • It might be also useful for time-lapse (4D) seismic monitoring for some oil fields.

38. Technical Contributions (II) • Apply interferometric migration to salt flank imaging with VSP data: • A huge chunk of overburden is ignored, so that the imaging is not only efficient, but also robust to velocity estimation errors. • Other vertical structures, such as faults that are difficult to image by surface seismic surveys could also be imaged.

39. The End Thank you.