1. Mitigation of RTM Artifacts with Migration Kernel Decomposition Ge Zhan* and Gerard T. Schuster King Abdullah University of Science and Technology June 7, 2012

2. Outline Introduction Method Examples  Two-layer model  BP salt model Conclusions 025 12.5 0 X (km) Depth (km) 08 4 0 X (km) Depth (km) 2 km/s 3 km/s

3. Outline Introduction Method Examples  Two-layer model  BP salt model Conclusions

4. Introduction --- Reverse-time migration (RTM) Benefits : Images any dipping structure; Accounts for multiple arrivals; and etc. Problems: intensive computational costssevere migration artifacts

5. Introduction --- RTM artifacts RTM artifacts usually present as strong-amplitude, low-frequency noises in the migration image. artifacts contaminate image Various remedies have been proposed to suppress RTM artifacts:  Smooth the velocity model before migration ( Loewenthal et al., 1987 );  Low-cut filtering on migrated images ( Mulder and Plessix, 2003 );  Directional damping to non-reflection wave equation ( Fletcher et al., 2005 );  Least-squares migration ( Nemeth et al., 1999; Guitton et al., 2006 );  Migration deconvolution ( Hu et al., 2001; Yu et al., 2006 );  Poynting-vector imaging condition ( Yoon and Marfurt, 2006 );  Wavefield decomposition using Hilbert transform ( Liu et al., 2007; 2011 ).

6. Outline Introduction Method Examples  Two-layer model  BP salt model Conclusions

7. Method --- Seismic Survey

8. Method --- Seismic Modeling Recorded seismic data

9. Method --- Reverse Time Migration (RTM) Migration of seismic data

10. Method --- Reverse Time Migration (RTM) Migration of seismic data

11. Method --- Reverse Time Migration (RTM) Migration of seismic data

12. Method --- Reverse Time Migration (RTM) Migration of seismic data

13. Method --- Reverse Time Migration (RTM) Migration of seismic data

14. Method --- Reverse Time Migration (RTM) Migration of seismic data

15. Method --- Generalized Diffraction Migration (GDM) Migration of seismic data

16. Method --- GDM Workflow 1.Compute & save Green’s functions for a given migration velocity; 2.Filter the Green’s functions into downgoing and upgoing components in F-K domain; 3.Convolve the appropriate components of filtered Green’s function to form the migration kernel; 4.Dot product of the migration kernel with the recorded seismic data to get the migration image. T x shotgather T x Migration Kernel

17. Outline Introduction Method Examples  Two-layer model  BP salt model Conclusions

18. 08 4 0 X (km) Depth (km) GDM 08 4 0 X (km) Depth (km) 2 km/s 3 km/s 08 4 0 X (km) Depth (km) 08 4 0 X (km) Depth (km) 08 4 0 X (km) Depth (km) RT M Examples --- two-layer model

19. Outline Introduction Method Examples  Two-layer model  BP salt model Conclusions

20. Examples --- BP salt model 025 12.5 0 X (km) Depth (km) 1.5 4.5 km/s Vp 025 12.5 0 X (km) Depth (km) 1-shot RTM image 025 12.5 0 X (km) Depth (km) Stacked RTM image 025 12.5 0 X (km) Depth (km) High-pass-filtered RTM image

21. Examples --- BP salt model 025 12.5 0 X (km) Depth (km) Standard RTM w/ filtering 025 12.5 0 X (km) Depth (km) Horizontal GDM image 025 12.5 0 X (km) Depth (km) Vertical GDM image 025 12.5 0 X (km) Depth (km) Stacked GDM image 025 12.5 0 X (km) Depth (km)

22. Outline Introduction Method Examples  Two-layer model  BP salt model Conclusions

23. 1). The kernel of RTM imaging operator is decomposed into products of downgoing and upgoing Green’s functions. 2). This decomposition leads to an imaging algorithm with fewer artifacts and a higher-quality RTM image. 3). Advantage: deterministic filtering of RTM kernel can be directly applied to reduce migration artifacts, mitigate multiples and eliminate aliasing artifacts. 4). Drawback: significantly more storage capacity and I/O time than standard RTM. Conclusions 5). There are still some residual artifacts, which can be further eliminated by least-squares migration.

24. We thank the sponsors of the Center for Subsurface Imaging and Fluid Modeling (CSIM) at KAUST for their support. Acknowledgments We also thank BP for making the BP 2007 salt model available.

25. Question or Suggestion? Thank you for your attention!