Salt Flank Imaging by VSP Interferometry

1. Salt Flank Imaging by VSP Interferometry Ruiqing He University of Utah Feb., 2006

2. Outline • Introduction • VSP Interferometric Methods • A Synthetic Test • Existing Problems • Conclusion and Future Work

3. Outline • Introduction • VSP Interferometric Methods • A Synthetic Test • Existing Problems • Conclusion and Future Work

4. Horizontal Imaging Overburden Overburden VSP Interferometry Introduction Salt Proximity Survey Virtual source: Bakulin & Calvert

5. Outline • Introduction • VSP Interferometric Methods • A Synthetic Test • Existing Problems • Conclusion and Future Work

6. Crosscorrelation Migration Steps: 1, Crosscorrelate each WR & Ws, 2, The crosscorrealtion data as a virtual source data, with source at s’. 3. Migrate the virtual source data from s’ to g. s s’ Ws G g WR

7. Wave-equation Implementation Steps: 1, Forward extrapolate Ws, 2, Backward extrapolate WR, 3. Apply a reverse-time migration imaging condition. s s’ Ws G g WR

8. Outline • Introduction • VSP interferometric methods • A synthetic test • Existing problems • Conclusion and future work

9. A Synthetic Experiment 0 10 shots Depth (m) 94 geophones 5500 7000 0 Offset (m)

10. Synthetic Data by FD 0 Other incident waves and their reflections Direct wave Time (s) Reflected direct wave 3 27000 Depth (m) 5500

11. Target Velocity Model Real model Expanded sedimentary model

12. Result after X-correlation Migration 2700 Depth (m) 5500 0 Offset (m) 1700

13. Result after Wave-Equation Migration 2700 Depth (m) 5500 0 Offset (m) 1700

14. Outline • Introduction • VSP interferometric methods • A synthetic test • Existing problems • Conclusion and future work

15. Problem I: cross talk • Left-going source wavefield and right-going reflection wavefield not separated. • Suppression: • Deconvolution-based imaging condition. (Muijs et al, 2005)

16. 3D out-of-plane waves problem Problem: the recorded reflection is from an out-of-plane wave; and the recorded incident wave, after reflection by the salt flank, is not recorded ! To really enjoy the “free lunch” of bypassing overburden, controls of limiting out-of-plane waves should be applied.

17. Outline • Introduction • VSP interferometric methods • A synthetic test • Existing problems • Conclusion and future work

18. Conclusion & Future Work • Two methods are proposed for 2D VSP salt flank imaging that requires no information about the overburden. • Separation of the source wavefield and reflection wavefiled, or suppression of cross talk will help imaging. • Limiting 3D out-of-plane waves in a 2D survey is highly desirable.

19. Acknowledgement • Thanks to UTAM 2005 sponsors for financial support. • Thanks to BP for providing internship.