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New methodology for anisotropic PP-PS
migration-based velocity analysis
Constantin Gerea, STATOIL
Laurence Nicoletis, IFP
FORCE workshop, 6 feb 2002, NPD, Stavanger
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Outline
Sensitivity of C-wave residual moveout in the
prestack migrated domain
Methodology for joint PP-PS migration velocity
analysis in v(z) VTI media
Tests on 2-D elastic synthetic data sets
Applications on the 2D-4C OBC seismic data set
Mahogany experience.
Conclusions
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Imaging Equations
Residual moveout
(Liu and Bleistein, 1995)
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Sensitivity of C-wave reflection moveout
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CCP location of C- waves
Xs
Xr
CCP
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Methodology
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Outline
offset
offset
offset
0
0
0
t
t
t
SEG-EAGE SRW, October 2000, Boise, ID
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2-D Elastic Synthetic Model
- 2000
VP (m/s)
X(m)
Target Zone
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PS-wave stack after co-scaling
Using updated velocity model
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PS-wave post-migration stack
Using  true  velocity model
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Scan and update of VS/VP ratio
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Anisotropic velocity analysis
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- 3000
- 3000
3000
0
3000
0
- 3000
3000
0
0.2
Time (s)
2.2
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Updated velocity model
2.2
3.5
Km/s
1.2
1.0
0
0.12
-0.14
0
timePP
timePP
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Mahogany experience
Courtesy of Phillips, Anadarko, BP and
Schlumberger
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Time PP (s)
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2.4
Time PP (s)
3.0
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PP-wave Post-Stack Time Migration
514
1314
CDP
914
0.2
Time PP (s)
conventional
3.5
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PP-wave PreStack Time Migration
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PS-wave Post-Stack Time Migration
positive offsets
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PS-wave PreStack Time Migration
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Scan over Vp/Vs ratio
994
CDP
0.2
Time (s)
PP-wave
PS-wave
3.5
Vp/Vs
6.0
2.0
Time (s)
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Average Vp/Vs velocity ratio
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Final average velocity model
CDP
CDP
h
Vp2 m/s
Time PP
geff
Vc2 m/s
Time PP
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Conclusions
Only 2 velocity parameters are necessary and
sufficient to describe the C-wave residual
moveout in the prestack migrated domain
Vc2 governs the parabolic moveout and geff the
linear moveout.
Semblance analysis performed in the CIGs has been
used to optimize these 2 parameters.
In the presence of lateral velocity variations
the estimated geff parameter differs from the
vertical geff.
The MVA methodology was succesfully applied on
the 2D-4C OBC seismic data set, Mahogany field,
Gulf of Mexico.
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Acknowledgements
IFP and CGG Multicomponent Seismic Teams