[PPT] - Wave-Equation Migration Velocity Analysis Paul Sava and Biondo Biondi PowerPoint Presentation

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Wave-Equation Migration Velocity Analysis

Paul Sava and Biondo Biondi* Stanford Exploration Project Stanford University EAGE 2004 Workshop on Velocity

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Deep-water subsalt imaging

1) Potentials of wavefield-continuation methods can be fulfilled only if we use MVA methods based on:

Wavefield-continuation migration
Salt-boundary picking
Below salt Common Image Gathers (CIG)
Wavefield-continuation velocity updating

2) We may need to go beyond downward-continuation migration methods and … be able to perform MVA

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Deep-water subsalt imaging - Velocity problem?

1) Potentials of wavefield-continuation methods can be fulfilled only if we use MVA methods based on:

Wavefield-continuation migration
Salt-boundary picking
Below salt Common Image Gathers (CIG)
Wavefield-continuation velocity updating

2) We may need to go beyond downward-continuation migration methods and … be able to perform MVA

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Deep-water subsalt imaging - Illumination?

1) Potentials of wavefield-continuation methods can be fulfilled only if we use MVA methods based on:

Wavefield-continuation migration
Salt-boundary picking
Below salt Common Image Gathers (CIG)
Wavefield-continuation velocity updating

2) We may need to go beyond downward-continuation migration methods and … be able to perform MVA

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“Simple” wavepath with f=126 Hz

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“Complex” wavepath with f=126 Hz

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“Messy” wavepath with f=126 Hz

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“Messy” wavepath with f=13 Hz

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“Messy” wavepath with f=15 Hz

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“Messy” wavepath with f=112 Hz

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“Messy” wavepath with f=116 Hz

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“Messy” wavepath with f=126 Hz

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Wavepaths in 3-D

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Wavepaths in 3-D – Banana or doughnuts?

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15 Brief history of velocity estimation with wavefield methods

Full waveform inversion (Tarantola, 1984, Pratt, today)
Diffraction tomography (Devaney and Oristaglio, 1984)
Wave-equation tomography (Woodward, 1990; Luo and Schuster 1991)
Differential Semblance Optimization (Symes and Carazzone, 1991)

Challenges of velocity estimation with wavefield methods

Limitations of the first-order Born linearization (“Born limitations”)
Problems with large (in extent and value) velocity errors
Dependent on accurate amplitudes both in the data and in the modeling
Computational and storage requirements of explicit use of wavepaths

Velocity Analysis and wavefield methods

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16 Receivers Sources

Depth

γ1

Vmig = Vtrue

γ1 γ2 γ3

γ2 γ3

α

Velocity information in ADCIGs - Correct velocity

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17 Receivers Sources

Depth

γ1

Vmig < Vtrue

γ1 γ2 γ3

γ2 γ3

α

Vmig < Vtrue

Δl1 < Δl2 < Δl3 Δl2 Δl1 Δl3

Velocity information in ADCIGs - Low velocity

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18 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into Δz

3)

Invert Δz into Δs by solving: where Lray is given by raytracing

Ray-tomography Migration Velocity Analysis

( )

2 ray Ä

Ä min s z

s

Δ − L W

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19 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into ΔI

3)

Invert ΔI into Δs by solving: where Lwave is given by first-order Born linearization of wavefield continuation

( )

2 wave Ä

Ä min s I

s

Δ − L W

Wave-Equation Migration Velocity Analysis

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20 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into ΔI

3)

Invert ΔI into Δs by solving: where Lwave is given by first-order Born linearization of wavefield continuation

( )

2 wave Ä

Ä min s I

s

Δ − L W

Sava and Biondi (2004) Important!

Wave-Equation Migration Velocity Analysis

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wave

L

Ray tomography MVA  Wave-Equation MVA

ray

L

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wave

L

Ray tomography MVA  Wave-Equation MVA

ray

L

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wave

L

Ray tomography MVA  Wave-Equation MVA

ray

L

ΔI Δz

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24 1) Potentials of wavefield-continuation methods can be fulfilled only if we use MVA methods based on:

Wavefield-continuation migration
Salt-boundary picking
Below salt Common Image Gathers (CIG)
Wavefield-continuation velocity updating

2) We may need to go beyond downward-continuation migration methods and … be able to perform MVA

Deep-water subsalt data

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Deep-water subsalt data - Initial velocity

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Deep-water subsalt data - Initial velocity

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27 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into ΔI

3)

Invert ΔI into Δs by solving:

( )

2 wave Ä

Ä min s I

s

Δ − L W

Deep-water subsalt data – WEMVA step 1)

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28 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into ΔI

3)

Invert ΔI into Δs by solving:

( )

2 wave Ä

Ä min s I

s

Δ − L W

Deep-water subsalt data – WEMVA step 1)

Δρ=ρ−1

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biondo@stanford.edu

29 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into ΔI

3)

Invert ΔI into Δs by solving:

( )

2 wave Ä

Ä min s I

s

Δ − L W

Deep-water subsalt data – WEMVA step 2)

ΔI

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biondo@stanford.edu

30 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into ΔI

3)

Invert ΔI into Δs by solving:

( )

2 wave Ä

Ä min s I

s

Δ − L W

Deep-water subsalt data – WEMVA step 2)

Δρ=ρ−1

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31 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into ΔI

3)

Invert ΔI into Δs by solving:

( )

2 wave Ä

Ä min s I

s

Δ − L W W

Deep-water subsalt data – WEMVA step 3)

ΔI W

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32 1)

Measure errors in ADCIGs by measuring curvature (ρ)

2)

Convert measured ρ into ΔI

3)

Invert ΔI into Δs by solving:

( )

2 wave Ä

Ä min s I

s

Δ − L W

s0+Δs s0

Deep-water subsalt data – WEMVA step 3)

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Deep-water subsalt data – Initial velocity

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Deep-water subsalt data – Velocity after 2 iterat.

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Deep-water subsalt data – Initial image Image

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Image Deep-water subsalt data – Image after 2 iterat.

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Deep-water subsalt data – Initial ADCIGs ADCIGs

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ADCIGs Deep-water subsalt data – ADCIGs after 2 iterat.

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Deep-water subsalt data – Initial ADCIGs ADCIGs

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ADCIGs Deep-water subsalt data – ADCIGs after 2 iterat.

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Δρ Δρ=ρ-1 White  flat ADCIGs Deep-water subsalt data – Initial Δρ Δρ=ρ-1

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Deep-water subsalt data – Δρ Δρ after 2 iterations Δρ Δρ=ρ-1 White  flat ADCIGs

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Deep-water subsalt data – W after 2 iterations Weights White  reliable ρ picks

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Ray-based Migration Velocity Analysis (MVA) methods

have been successful in complex structure, but they are challenged by subsalt velocity estimation.

Conclusions

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Ray-based Migration Velocity Analysis (MVA) methods

have been successful in complex structure, but they are challenged by subsalt velocity estimation.

Wave-equation MVA (WEMVA) can be accomplished while

preserving the work-flow of conventional ray-based MVA methods.

Conclusions

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Ray-based Migration Velocity Analysis (MVA) methods

have been successful in complex structure, but they are challenged by subsalt velocity estimation.

Wave-equation MVA (WEMVA) can be accomplished while

preserving the work-flow of conventional ray-based MVA methods.

The velocity function estimated by the use of our WEMVA

method results in flatter ADCIGS and more coherent reflectors, even if we started from a high-quality velocity function that was estimated with ray-based MVA.

Conclusions

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Ray-based Migration Velocity Analysis (MVA) methods

have been successful in complex structure, but they are challenged by subsalt velocity estimation.

Wave-equation MVA (WEMVA) can be accomplished while

preserving the work-flow of conventional ray-based MVA methods.

The velocity function estimated by the use of our WEMVA

method results in flatter ADCIGS and more coherent reflectors, even if we started from a high-quality velocity function that was estimated with ray-based MVA.

Poor illumination prevents the extraction of reliable velocity

information from ADCIGs at every location, and thus presents a challenge also for WEMVA.

Conclusions

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Acknowledgments

BP and ExxonMobil, and Frederic Billette at BP, for Deep Water GOM data. Total for North Sea data set. SMAART JV and J. Paffenholz (BHP) for the Sigsbee data set. SEP sponsors for financial support.

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