1. 3D Wave-equation Interferometric Migration of VSP Free-surface Multiples Ruiqing He University of Utah Feb., 2006

2. Outline Introduction Wave-equation Interferometric Migration (WEIM) A Synthetic Test Application to A Field 3D VSP Data Set Conclusion

3. Outline Introduction Wave-equation Interferometric Migration (WEIM) A Synthetic Test Application to A Field 3D VSP Data Set Conclusion

4. Introduction Migration of VSP multiples has a larger imaging area than migration of primaries.

5. Mirror image Published Methods Mirror imaging condition: transfer to a migration of primaries imaging condition. Real model Crosscorrelation migration: transfer VSP Crosscorrelation migration: transfer VSP data to CDP data. data to CDP data.

6. Difficulties Crosscorrelation is not cheap. Kirchhoff migration is not cheap. Ray tracing. Ray tracing. Storage of time tables. Storage of time tables. 3D. 3D.

7. Outline Introduction Wave-equation Interferometric Migration (WEIM) A Synthetic Test Application to A Field 3D VSP Data Set Conclusion

8. WEIM Reciprocity

9. Line-source Ray tracing Known medium Unknown medium The picked time is imposed as an initial condition in ray tracing.

10. Advantages of WEIM Experience similar velocity estimation errors as migrating CDP primaries. For each receiver gather, only one line- source ray tracing, and one wavefield extrapolation is needed. In 3D VSP, the saving of ray tracing and timetable storage is enormous.

11. Outline Introduction Wave-equation Interferometric Migration (WEIM) A Synthetic Test Application to A Field 3D VSP Data Set Conclusion

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

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

14. Outline Introduction Wave-equation Interferometric Migration (WEIM) A Synthetic Test Application to A Field 3D VSP Data Set Conclusion

15. Acquisition Geometry 12 geophones at an interval of 15.25 m. ~ 11 km ~ 4.5 km deep

16. 2D WEIM Result Offset (km) 011 0 7.5 Depth (m)

17. 3D WEIM Result Migration of only one receiver gather

18. Slice Movie Migration of only one receiver gather

19. Outline Introduction Wave-equation Interferometric Migration (WEIM) A Synthetic Test Application to A Field 3D VSP Data Set Conclusion

20. Conclusion Proposed 3D WEIM, which is very efficient for migrating 3D VSP multiples. Migration of 3D VSP free-surface multiples provides an imaging area comparable to a conventional 3D CDP survey, yet the data processing cost is much reduced.

21. Acknowledgement Thanks to UTAM 2005 sponsors for financial support.