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Local Reverse Time Migration with VSP Green’s Functions

PhD Defense. Local Reverse Time Migration with VSP Green’s Functions. Xiang Xiao UTAM, Univ. of Utah May 1, 2008. 99 pages. Outline. Introduction and overview SSP  VSP  SWP interferometric transform Local reverse time migration: horizontal reflector imaging

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Local Reverse Time Migration with VSP Green’s Functions

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  1. PhD Defense Local Reverse Time Migration with VSP Green’s Functions Xiang Xiao UTAM, Univ. of Utah May 1, 2008 99 pages

  2. Outline • Introduction and overview • SSP VSP  SWP interferometric transform • Local reverse time migration: horizontal reflector imaging • Local reverse time migration: salt flank imaging with transmitted P-to-S waves • Summary Overview Local RTM Local RTM PS Summary SSPVSP

  3. Outline • Introduction and overview • SSP VSP  SWP interferometric transform • Local reverse time migration: horizontal reflector imaging • Local reverse time migration: salt flank imaging with transmitted P-to-S waves • Summary Overview Local RTM Local RTM PS Summary SSPVSP

  4. Model Data Time Depth Offset Offset Forward modelling r(x) D(g|s) Migration Image Inverse Migration m(x) Low subsalt resolution, Defocusing! Overview Local RTM Local RTM PS Summary SSPVSP

  5. Model- based Model- based * m(x) ~ ~ G(x|s) G(x|g)* ds s Subsalt Imaging D(g|s)dg g s D(g|s) g G(x|s) G(x|g) x Overview Local RTM Local RTM PS Summary SSPVSP

  6. Forward direct Backward reflection m(x) ~ ~ G(x|s) G(x|g)* D(g|s)dg g Subsalt Imaging * ds s s Errors in the overburden and salt body velocity model D(g|s) g G(x|s) G(x|g) x Defocusing Overview Local RTM Local RTM PS Summary SSPVSP

  7. Data- based G(x|s) Interferometric Imaging Model- based * m(x) ~ ~ G(x|g)* D(g|s)dg ds s g s g G(x|s) G(x|g) x Overview Local RTM Local RTM PS Summary SSPVSP

  8. Local Reverse Time Migration Backward Direct wave G(x|s)= G(x|g’)* D(g’|s)dg’ g’ Local VSP Green’s function s g G(x|s) G(x|g) x g’ Overview Local RTM Local RTM PS Summary SSPVSP

  9. Backward approx Backward reflection m(x) ~ ~ G(x|s) G(x|g)* D(g|s)dg g Local Reverse Time Migration * ds s s s g G(x|s) G(x|g) x g’ Overview Local RTM Local RTM PS Summary SSPVSP

  10. Outline • Introduction and overview • SSP VSP  SWP interferometric transform • Local reverse time migration: horizontal reflector imaging • Local reverse time migration: salt flank imaging by transmitted P-to-S waves • Summary Overview Local RTM Local RTM PS Summary SSPVSP

  11. Outline • SSP VSP  SWP interferometric transform • Motivation • Theory • Numerical Tests • SEG/EAGE salt model • Double datuming • Conclusions Overview Local RTM Local RTM PS Summary SSPVSP

  12. I. Why we need more VSP? SSP VSP • Surface related statics • Twice Once Seabed • Overburden velocity error • Twice Once • Raypath Salt • Longer Shorter • Attenuation • More Less • Frequency Target • Lower Higher • Resolution • Lower Higher Motivation SSPVSP Theory Numerical Tests Conclusions

  13. VSP RVSP SSP x B x B x B S2 S2 S2 A A A S1 S1 S1 RVSP VSP SSP G(B|A) ~ G(A|x)* G(B|x) How to get more VSP? dx ~ S2 Motivation SSPVSP Theory Numerical Tests Conclusions

  14. 3D Application 3DSSP 3D VSP Low fold Naturally datuming ! High fold ! SSP + VSP RVSP! 3D RVSP Motivation SSPVSP Theory Numerical Tests Conclusions

  15. Receiver coverage Shot coverage S Seabed Salt SSP/RVSP aperture Target X g VSP aperture Motivation SSPVSP Theory Numerical Tests Conclusions

  16. SSP, VSP Well log High folds ! Salt SSP + VSP RVSP! 3D RVSP Use it, or lost it… Better Geologic interpretation ! Better image under the salt ! Motivation SSPVSP Theory Numerical Tests Conclusions

  17. What is the benefit ? SSP + VSP  RVSP • Sources are closer to the target; • Higher fold virtual RVSP data are obtained; • No velocity model is needed; • Multi-arrival are considered; Salt Motivation SSPVSP Theory Numerical Tests Conclusions

  18. VSP VSP Virtual Source Gather s s s g’ g’ g’ g g g VSP VSP SWP G(g’|s)* G(g|s) G(g|g’) ~ How to skip overburden? No velocity model is needed ! dx ~ S Motivation SSPVSP Theory Numerical Tests Conclusions

  19. Virtual Source Gather s g’ g Application Application of VSPSWP transform: • Salt flank imaging • P and S wave checkshot • Sediment imaging • Multiple/teleseismic imaging • 4D Reservoir monitoring • Shear wave splitting and crack orientation • Seismic while drilling • …… Motivation SSPVSP Theory Numerical Tests Conclusions

  20. Outline • SSP VSP  SWP interferometric transform • Motivation • Theory • Numerical Tests • SEG/EAGE model • Double datuming • Conclusions Overview Local RTM Local RTM PS Summary SSPVSP

  21. SEG/EAGE Salt Model P-wave velocity model Velocity (m/s) 0 4500 Depth (m) 3600 1500 -7850 Offset (m) 7850 Motivation SSPVSP Theory Numerical Tests Conclusions

  22. P-wave velocity model Velocity (m/s) 0 4500 Depth (m) 3600 1500 -7850 Offset (m) 7850 SSP Data Geometry… SSP Motivation SSPVSP Theory Numerical Tests Conclusions

  23. Synthetic SSP CSG 0 Time (s) 6 -2000 2000 Offset (m) Data Motivation SSPVSP Theory Numerical Tests Conclusions

  24. P-wave velocity model Velocity (m/s) 0 4500 Depth (m) 3600 1500 -7850 Offset (m) 7850 VSP Geometry… Motivation SSPVSP Theory Numerical Tests Conclusions

  25. Synthetic SSP CSG Synthetic VSP CRG 0 0 Time (s) 6 6 -7850 7850 -7850 7850 Offset (m) Offset (m) Data Time (s) Motivation SSPVSP Theory Numerical Tests Conclusions

  26. Synthetic RVSP CSG 0 Time (s) 6 Redatumed RVSP 0 Traces comparisons Zoom area Amplitude Time (s) 2 Time (s) 6 6 -7850 7850 Offset (m) 1.4 kmComparison

  27. Zoom View of Traces Direct waves are cut Redatumed RVSP trace poor data folds Normalized Amplitude 3 Time (s) 5.5 Motivation SSPVSP Theory Numerical Tests Conclusions

  28. P-wave velocity model Velocity (m/s) 0 4500 Depth (m) 3600 1500 -7850 Offset (m) 7850 Another Datuming Results Motivation SSPVSP Theory Numerical Tests Conclusions

  29. Synthetic RVSP CSG 0 Time (s) 6 Redatumed RVSP 0 Time (s) 6 -2000 2000 Offset (m) 2.4 kmComparison Traces comparisons Amplitude 2 Time (s) 6

  30. Zoom view Direct waves are cut Redatumed RVSP trace poor data folds Normalized Amplitude 2.5 6 Time (s) Motivation SSPVSP Theory Numerical Tests Conclusions

  31. SEG/EAGE Salt Model P-wave velocity model Velocity (m/s) 0 4500 Depth (m) 3600 1500 -7850 Offset (m) 7850 Motivation SSPVSP Theory Numerical Tests Conclusions

  32. Shot 320 SSP primary WEM 20 Hz 1.5 Depth (km) 3.5 Shot 320 RVSP WEM 20 Hz 1.5 Depth (km) 3.5 -4 4 Offset (km)

  33. 33 shots SSP WEM 20 Hz SEG/EAGE salt model 0 Depth (km) 3.6 33shots VSP WEM 20 Hz 0 Depth (km) 3.6 -4 4 Offset (km) 33 RVSP+VSP WEM 20 Hz -4 4 Offset (km)

  34. s g s g s’ s’ s’ SSPVSPSWP Transform g g g’ s’ g’ s’ g’ Motivation SSPVSP Theory Numerical Tests Conclusions

  35. 1% error in migration model 645 shots SSP WEM 0 Depth (km) 3.6 2% error in migration model 3% error in migration model 0 Depth (km) 3.6 -8 8 -8 8 Offset (km) Offset (km)

  36. 1% error in migration model 33 shots VSP WEM 0 Depth (km) 3.6 2% error in migration model 3% error in migration model 0 Depth (km) 3.6 -8 8 -8 8 Offset (km) Offset (km)

  37. 645 shots SSP primary WEM 20 Hz 0 Depth (km) 3.5 Shot 320 BSSP WEM 20 Hz 1.5 Depth (km) 3.5 -8 8 Offset (km)

  38. 645 shots SSP primary WEM 20 Hz 0 Depth (km) 3.5 Shot 320 BSSP WEM 20 Hz 1.5 Depth (km) 3.5 -8 8 Offset (km)

  39. Conclusions • Natural datuming, no velocity model is needed ! • Higher fold virtual VSP data are obtained ! • Source are closer to the target, less approximation. • Better resolution. Motivation SSPVSP Theory Numerical Tests Conclusions

  40. Outline • Introduction and overview • SSP VSP  SWP interferometric transform • Local reverse time migration: horizontal reflector imaging • Local reverse time migration: salt flank imaging with transmitted P-to-S waves • Summary Overview Local RTM Local RTM PS Summary SSPVSP

  41. Outline • Local reverse time migration: horizontal reflector imaging • Motivation • Theory • Numerical Tests • Sigsbee VSP Data Set • GOM VSP Data Set • Conclusions Motivation Local RTM Theory Numerical Tests Conclusions

  42. VSP Forward Modeling s VSP data g D(g|s) x Motivation Local RTM Theory Numerical Tests Conclusions

  43. Reverse Time Migration s VSP data g D(g|s) x Motivation Local RTM Theory Numerical Tests Conclusions

  44. Forward direct Backward data G(x|s) G(x|g)* D(g|s)dg g Reverse Time Migration * m(x) ~ ~ ds s s G(x|g) G(x|s) g Backward D(g|s) Forward direct x Motivation Local RTM Theory Numerical Tests Conclusions

  45. Reverse Time Migration (RTM) • Forward direct: • Salt velocity model is required, but hard to build. 2) Errors due to imperfect velocity models. 3) Need to estimate statics, anisotropy, etc. s G(x|g) G(x|s) g Backward D(g,s) Forward direct x Motivation Local RTM Theory Numerical Tests Conclusions

  46. VSPSWP Interferometry s g x Migrate virtual source gather D(g|g’) g’ Limitations 1) s and x are at different sides of the well 2) Image near vertical structures Motivation Local RTM Theory Numerical Tests Conclusions

  47. Outline • Local reverse time migration: horizontal reflector imaging • Motivation • Theory • Numerical Tests • Sigsbee VSP Data Set • GOM VSP Data Set • Conclusions Motivation Local RTM Theory Numerical Tests Conclusions

  48. Key Idea of Local RTM (a) VSP data: P(g|s)=T(g|s)+R(g|s) s g Reflection R(g|s) x Transmission T(g|s) Motivation Local RTM Theory Numerical Tests Conclusions

  49. (a) VSP data: P(g|s)=T(g|s)+R(g|s) s g R(g|s) x (b) Backward reflection (c) Backward transmission T(g|s) s R(x|s)= G(x|g)*R(g|s) T(x|s)= G(x|g)*T(g|s) g g g R(g|s) x x x T(g|s) R(g|s) (d) Crosscorrelation m(x)= R(x|s)*T(x|s) g s g Key Idea of Local RTM s Local VSP Green’s function Motivation Local RTM Theory Numerical Tests Conclusions

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