1. Mathias Alerini Gemini kollokvium 28 02 2008
Seismic angle migration: an adaptive limitation of the operator aperture
Mathias Alerini
Gemini kollokvium

2. PostDoc work... With Pr. Bjørn Ursin Sponsored by NFR
(grants /I30 and /S30 and the ROSE project)
July 2005 to December
in parallel to many other things...

3. Seismic Data
Amplitude
time

4. Seismic Data

5. Imaging process
Seismic survey
Seismic processing
Subsurface
Data

6. + Velocity of seismic waves
Seismic migration
From seismic trace to image position (& dynamic information) x
+ Velocity of seismic waves

7. Seismic migration Kirchhoff type M s r T + Velocity
For all M points along the curve, the travel times T(s,M,r) are equal
Recorded energy comes from somewhere along the curve!

8. Seismic migration Kirchhoff type
Recorded energy is somewhere along the curve!
+ Velocity

9. Seismic migration Common Image gather offset s s s s s s s s s s r r rz0 x z

10. Seismic migration Common Image gather angle s s s s s s s s s s r r rz0 x z

11. Angle Migration: Advantages
Complex geological setting
(Strong lateral velocity variations) 1 2 h s r
Triplications:
1 offset, 2 (e.g.) angles
Artifacts
AVO/AVA:
Reflection coefficients depends on the angle and not the offset !

12. Limitation of the migration operator
The traveltime tells us that the recorded energy comes from somewhere along the curves but the migration result tells us the energy comes from the envelop

13. Limitation of the migration operator
We just need this information.
The rest :
increases the computation time
adds noise

14. Limitation of the migration operator
The noise is not completely destroyed by the summation process

15. Limitation of the migration operator
We want to keep only constructive interferences between the specular ray (respects Snell-Descartes) and the migrated ray s r
migrated ray vs
specular ray

16. Limitation of the migration operator
at the image point s s r r  
Difference in traveltime between the specular ray and the migrated ray
relation to the migration operator aperture

17. Limitation of the migration operator
at the image point, looking at one side
isochrone = same traveltime 
but...

18. Limitation of the migration operator
sub-horizontal rays...
isochrone = same traveltime 
a small angles produces a large traveltime difference

19. Limitation of the migration operator
sub-horizontal rays...
isochrone = same traveltime 
tangent to the isochrone

20. Limitation of the migration operator
sub-horizontal rays...
isochrone = same traveltime 
tangent to the isochrone
... it is equivalent to the Young’s experiment
Observed interferences
Signals in phase

21. Limitation of the migration operator
results: 25m between srcs and recs
No LAM
LAM

22. Limitation of the migration operator
results: 100m between srcs and 100m between recs
No LAM
LAM

23. Conclusion Our Limitation of the migration aperture is
easy to implement in an existing code
easy to use
can handle multi-orientations (faults)
can include easily a local error on the geological dip
gave very good results !

24. ... finally
codes have been written, rewritten in a coherent way with new tools and then ported to the cluster...
... or how to do 3 times the same work...

25. ... finally
codes have been written, rewritten in a coherent way with new tools and then ported to the cluster...
... or how to do 3 times the same work...
“Through continuous efforts we succeed eventually. Thus, the more it fails, the greater chance that it succeeds”