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


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...


Seismic Data

time

Amplitude


Seismic Data


Imaging process

Seismic survey

Seismic processing

Subsurface Data


Seismic migration

From seismic trace to image position (& dynamic information)

x

+ Velocity of seismic waves


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


Seismic migration

Kirchhoff type

+ VelocityRecorded energy is somewhere along the curve!


Seismic migration

Common Image gather

s rs r r r r r r rrssssssss

x

z

z0

offset


Seismic migration

Common Image gather

s rs r r r r r r rrssssssss

x

z

z0

angle


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 !


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



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



The noise is not completely destroyed by the summation process

The noise is not completely destroyed by the summation process



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



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



at the image point, looking at one side

T

isochrone = same traveltime

but...



sub-horizontal rays...

T


a small angles produces a large traveltime difference




T


tangent to the isochrone




T


tangent to the isochrone

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

Signals in phase

Observed interferences



results: 25m between srcs and recs

No LAM LAM



results: 100m between srcs and 100m between recs

No LAM LAM


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 !


... 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...


... 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”

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

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