sintef petroleum research 1 seismic angle migration: an adaptive limitation of the operator aperture...

1SINTEF Petroleum Research

Seismic angle migration: an adaptive limitation of the operator aperture

Mathias Alerini

Gemini kollokvium

28 02 2008

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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

time

Amplitude

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Seismic Data

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Imaging process

Seismic survey

Seismic processing

Subsurface Data

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Seismic migration

From seismic trace to image position (& dynamic information)

x

+ Velocity of seismic waves

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Seismic migration

Kirchhoff type

+ Velocity

Recorded energy comes from somewhere along the curve!

For all M points along the curve, the travel times T(s,M,r) are equal

M

s r

T

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Seismic migration

Kirchhoff type

+ VelocityRecorded energy is somewhere along the curve!

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Seismic migration

Common Image gather

s rs r r r r r r rrssssssss

x

z

z0

offset

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Seismic migration

Common Image gather

s rs r r r r r r rrssssssss

x

z

z0

angle

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Angle Migration: Advantages

Complex geological setting (Strong lateral velocity variations)

Triplications: 1 offset, 2 (e.g.) angles

Artifacts

1

2

hs r

AVO/AVA:Reflection coefficients depends on the angle and not the offset !

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

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

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

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

migrated ray vs

specular ray

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Limitation of the migration operator

at the image point

s rrs

Difference in traveltime between the specular ray and the migrated ray

relation to the migration operator aperture

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

T

isochrone = same traveltime

but...

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Limitation of the migration operator

sub-horizontal rays...

T

isochrone = same traveltime

a small angles produces a large traveltime difference

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Limitation of the migration operator

sub-horizontal rays...

T

isochrone = same traveltime

tangent to the isochrone

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Limitation of the migration operator

sub-horizontal rays...

T

isochrone = same traveltime

tangent to the isochrone

... it is equivalent to the Young’s experiment

Signals in phase

Observed interferences

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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”