Reverse-Time Migration By A Variable Grid-Size And Time-Step Method Yue Wang University of Utah

Reverse-Time MigrationReverse-Time MigrationBy A Variable Grid-Size By A Variable Grid-Size And Time-Step MethodAnd Time-Step Method

Yue WangYue Wang

University of UtahUniversity of Utah

OutlineOutline

• BackgroundBackground

• Motivation & ObjectiveMotivation & Objective

• MethodologyMethodology

• Numerical ExamplesNumerical Examples

• ConclusionsConclusions

Forward ModelingForward Modeling

Distance (km)Distance (km)

Dep

th (

km

)D

epth

(k

m)

11

00

00 4.54.5

*

obsobs

SourceSource Geophone LineGeophone Line

Reverse Time MigrationReverse Time Migration


Dep

th (

km

)D

epth

(k

m)

11

00

00 4.54.5

obsobs

Extrapolated WavefieldExtrapolated Wavefieldobsobs

Reversed tracesReversed traces

Reverse-Time MigrationReverse-Time Migration

Extrapolated WavefieldExtrapolated Wavefield

Imaging ConditionImaging Condition

Migration SectionMigration Section

OutlineOutline






Ocean-Bottom SurveyOcean-Bottom Survey


Dep

th (

km

)D

epth

(k

m)

11

00

00 4.54.5

*SourceSource Geophone LineGeophone Line

ProblemProblem


Dep

th (

km

)D

epth

(k

m)

11

00

00 4.54.5

*Receiver-side MultiplesReceiver-side Multiples

Synthetic Shot GatherSynthetic Shot GatherT

ime

(s)

Tim

e (s

)


Receiver side multiplesReceiver side multiples

22

00

0.90.9 3.63.6

Field DataField DataT

ime

(s)

Tim

e (s

)

Distance (m)Distance (m)44

00

-80-80 19001900


Time MigrationTime MigrationT

ime

(s)

Tim

e (s

)

Distance (m)Distance (m)44

00

-80-80 19001900


ObjectiveObjective

• Using both primary and receiver Using both primary and receiver side multiple reflections for side multiple reflections for imaging by reverse-time migration.imaging by reverse-time migration.

• Fast Reverse-Time MigrationFast Reverse-Time Migration

• Elastic RT Migration for Land & Elastic RT Migration for Land & Ocean Bottom Multicomponent Ocean Bottom Multicomponent DataData

OutlineOutline






Ocean-Bottom SurveyOcean-Bottom Survey


Dep

th (

km

)D

epth

(k

m)

11

00

00

* PP VV

Up-goingUp-going

Multi-Component DataMulti-Component Data

Two RTM SchemesTwo RTM Schemes

•Migrate particle velocity only Migrate particle velocity only (conventional scheme)(conventional scheme)

•Migrate pressure and particle Migrate pressure and particle velocity simultaneouslyvelocity simultaneously

Key IdeaKey IdeaPrimary + Multiple Primary + Multiple

Correct Positions Correct Positions

P & V Scheme P & V Scheme

P & V SchemeP & V Scheme

Distance Distance

Dep

thD

epth

Correct PositionCorrect Position

Down-going wavesDown-going waves

Reversed TracesReversed TracesPP VV

Key IdeaKey IdeaPrimary + Multiple Primary + Multiple

Incorrect Positions Incorrect Positions

V-Only Scheme V-Only Scheme

Particle Velocity Only SchemeParticle Velocity Only Scheme

Distance Distance

Dep

th

Dep

th

IncorrectIncorrect

Reversed TracesReversed Traces

VV

Variable Grid-Size and Time-StepVariable Grid-Size and Time-Step

coarse grid, fine time stepcoarse grid, fine time step

coarse grid, coarse time stepcoarse grid, coarse time step

DistanceDistance

Dep

thD

epth

fine grid, fine time stepfine grid, fine time step

OutlineOutline






• Synthetic Marine DataSynthetic Marine Data

* 2D Elastic Salt Model* 2D Elastic Salt Model

* 3D Acoustic SEG/EAGE Model* 3D Acoustic SEG/EAGE Model

• 2D Land Data2D Land Data

Numerical ResultsNumerical Results

2-D Salt Model2-D Salt Model


Dep

th (

km

)D

epth

(k

m)

2.72.7

00

00 4.54.5

Shot GatherShot GatherPressurePressureVerticalVerticalHorizontalHorizontal

Tim

e (s

) T

ime

(s)

Distance (km)Distance (km)22

00

0.90.9 3.63.6 Distance (km)Distance (km)0.90.9 3.63.6 Distance (km)Distance (km)0.90.9 3.63.6

PSPS

PPPP

Kirchhoff MigrationKirchhoff Migration


Dep

th (

km

)D

epth

(k

m)

2.52.5

00

0.450.45 4.054.05



Dep

th (

km

)D

epth

(k

m)

2.52.5

00

0.450.45 4.054.05


Dep

th (

km

)D

epth

(k

m)

2.52.5

00

0.450.45 4.054.05

Particle-Velocity RT SchemeParticle-Velocity RT Scheme


Dep

th (

km

)D

epth

(k

m)

2.52.5

00

0.450.45 4.054.05

P & V RT SchemeP & V RT Scheme



Dep

th (

km

)D

epth

(k

m)

2.52.5

00

0.450.45 4.054.05






3-D SEG/EAGE Salt Model3-D SEG/EAGE Salt Model


Dep

th (

km

)D

epth

(k

m)

22

00

00 4.54.5

Ocean-BottomOcean-BottomGeophone LineGeophone Line

Exploding Exploding Reflector SourceReflector Source



Dep

th (

km

)D

epth

(k

m)

22

00

00 4.54.5



Dep

th (

km

)D

epth

(k

m)

22

00

00 4.54.5


Dep

th (

km

)D

epth

(k

m)

22

00

00 4.54.5



Dep

th (

km

)D

epth

(k

m)

22

00

00 4.54.5

P & V SchemeP & V Scheme



Dep

th (

km

)D

epth

(k

m)

22

00

00 4.54.5


Dep

th (

km

)D

epth

(k

m)

22

00

00 4.54.5







East Texas Land DataEast Texas Land Data

2.72.7

00Radial Component Radial Component Vertical Component Vertical Component

Tim

e (s

) T

ime

(s)

Trace NumberTrace Number Trace NumberTrace Number00 8080 00 8080

Weak Signal/Noise RatioWeak Signal/Noise Ratio

Reverse-Time Migration Reverse-Time Migration


Dep

th (

km

)D

epth

(k

m)

44

00

00 2727Distance (km)Distance (km)00 2727

Kirchhoff MigrationKirchhoff Migration(Vertical Component)(Vertical Component)

ConclusionsConclusions

• Uses primary and multiple reflections for imagingUses primary and multiple reflections for imaging

• Variable RTM Variable RTM 10 times faster10 times faster than standard RTM than standard RTM• Migrates land and marine multi-component dataMigrates land and marine multi-component data

AcknowledgementAcknowledgement

We are grateful to the 1999 sponsors We are grateful to the 1999 sponsors of the UTAM consortium for the of the UTAM consortium for the financial supportfinancial support

QuestionsQuestions

Please contact Yue Wang at:Please contact Yue Wang at:

[email protected]@mines.utah.edu

Documents

Reverse-Time Migration By A Variable Grid-Size And Time-Step Method Yue Wang University of Utah