Seismic angle migration: an adaptive limitation of the operator aperture

1
Seismic angle migration an adaptive limitation
of the operator aperture

• Mathias Alerini
• Gemini kollokvium
• 28 02 2008

2
PostDoc work...

• With Pr. Bjørn Ursin
• Sponsored by NFR
• (grants 159117/I30 and 162612/S30 and the ROSE
  project)
• July 2005 to December 2007...
• in parallel to many other things...

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Seismic Data
Amplitude
time
4
Seismic Data
5
Imaging process
Seismic survey
Seismic processing
Subsurface
Data
6
Seismic migration

• From seismic trace to image position ( dynamic
  information)

x
Velocity of seismic waves
7
Seismic migration

• Kirchhoff type

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!
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Seismic migration

• Kirchhoff type

Recorded energy is somewhere along the curve!
Velocity
9
Seismic migration

• Common Image gather

offset
s
r
s
r
r
r
r
s
s
s
s
s
s
s
s
r
r
r
r
z0
x
z
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Seismic migration

• Common Image gather

angle
s
r
s
r
r
r
r
s
s
s
s
s
s
s
s
r
r
r
r
z0
x
z
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Angle Migration Advantages
Complex geological setting (Strong lateral
velocity variations)
Triplications 1 offset, 2 (e.g.) angles
Artifacts
AVO/AVA Reflection coefficients depends on the
angle and not the offset !
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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
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Limitation of the migration operator

• We just need this information.
• The rest
• increases the computation time
• adds noise

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

• at the image point

s
r
r
s
?
?
Difference in traveltime between the specular ray
and the migrated ray relation to the migration
operator aperture
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Limitation of the migration operator

• at the image point, looking at one side

isochrone same traveltime
??
but...
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Limitation of the migration operator

• sub-horizontal rays...

isochrone same traveltime
??
a small angles produces a large traveltime
difference
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Limitation of the migration operator

• sub-horizontal rays...

isochrone same traveltime
??
tangent to the isochrone
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Limitation of the migration operator

• sub-horizontal rays...

isochrone same traveltime
??
tangent to the isochrone
... it is equivalent to the Youngs experiment
Observed interferences
Signals in phase
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Limitation of the migration operator

• results 25m between srcs and recs

No LAM
LAM
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Limitation of the migration operator

• results 100m between srcs and 100m between recs

No LAM
LAM
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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 !

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... 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...

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... 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