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WAVEFIELD PREDICTION OF WATER-LAYER-MULTIPLES. Ruiqing He University of Utah Feb. 2004. Outline. Introduction Theory Synthetic experiments Application to Unocal data Conclusion. Introduction. Primary-preserving multiple removal demands

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Wavefield prediction of water layer multiples

WAVEFIELD PREDICTION OF WATER-LAYER-MULTIPLES

Ruiqing He

University of Utah

Feb. 2004


Outline
Outline

  • Introduction

  • Theory

  • Synthetic experiments

  • Application to Unocal data

  • Conclusion


Introduction
Introduction

  • Primary-preserving multiple removal demands

  • accurate wavefield prediction of multiples.

  • Other works:

  • - Delft

  • - Amundsen, Ikelle, Weglein, etc.

  • Water layer multiples


Outline1
Outline

  • Introduction

  • Theory

  • Synthetic experiments

  • Application to Unocal data

  • Conclusion


Berryhill and wiggins s methods

Kirchhoff Summation

Forward extrapolate traces

down to water bottom

Kirchhoff Summation

Filtered Subtraction

Forward extrapolate bottom

traces up to receivers

 Emulated Muliples

Multiple

attenuation

Berryhill and Wiggins’s Methods

Off-shore

seismic data

Water surface

Receiver line

Water bottom


The proposed method
The proposed method

Decomposition

of

receiver-side

ghosts

Wave forward

extrapolation

to the water bottom

FD

Off-shore

seismic data

FD

FD

Multiples

with last

round-trip

in water layer

Primary-

preserving

multiple

removal

Wave forward

extrapolation

to the receivers

DS

filtering

FD: Finite Difference

DS: Direct (simple) Subtraction

Other multiple

attenuation


Why finite difference
Why Finite Difference?

  • Advantage

  • - speed

  • - convenience

  • - capability: heterogeneous medium

  • Disadvantage

  • - dispersion?: reality, high-order FD


Types of water layer multiples
Types of Water-Layer-Multiples

  • LWLM: Multiples that have the last round-trip in the water layer.

  • Other WLM: other water-layer-multiples except LWLM.


Wavefield extrapolation of rsg
Wavefield Extrapolation of RSG

RSG

Mirror image of

the Receiver line

Water surface

Receiver line

U

RSG


Decomposition of rsg

RSG

f

+

+

U

DATA

Decomposition of RSG

Mirror image of

the Receiver line

Water surface

Receiver line


Outline2
Outline

  • Introduction

  • Theory

  • Synthetic experiments

  • Application to Unocal data

  • Conclusion


Synthetic model
Synthetic Model

0

water

BSR

Depth

(m)

Salt dome

Sandstone

1500

0

3250

Offset (m)


Synthetic seismic data
Synthetic seismic data

400

Time

(ms)

2500

0

3250

Offset (m)


Decomposed rsg
Decomposed RSG

400

Time

(ms)

2500

0

3250

Offset (m)


Predicted lwlm
Predicted LWLM

400

Time

(ms)

2500

0

3250

Offset (m)


Waveform comparison between data rsg
Waveform Comparisonbetween Data & RSG

Data

RSG

Amplitude

2400

600

Time (ms)


Waveform comparison between data lwlm
Waveform Comparisonbetween Data & LWLM

Data

LWLM

Amplitude

2400

600

Time (ms)


Waveform comparison between data rsg lwlm
Waveform Comparisonbetween Data & RSG+LWLM

Data

RSG + LWLM

Amplitude

2400

600

Time (ms)


Elimination of rsg lwlm
Elimination of RSG & LWLM

400

Time

(ms)

2500

0

3250

Offset (m)


Further multiple attenuation
Further Multiple Attenuation

400

Time

(ms)

2500

0

3250

Offset (m)


Outline3
Outline

  • Introduction

  • Theory

  • Synthetic experiments

  • Application to Unocal data

  • Conclusion


Unocal field data
Unocal field data

600

Time

(ms)

2400

0

3175

Offset (m)


Inadequate rsg decomposition
Inadequate RSG Decomposition

600

Time

(ms)

2400

0

3175

Offset (m)


Emulated lwlm
Emulated LWLM

600

Time

(ms)

2400

0

3175

Offset (m)


Waveform comparison between data emulated lwlm
Waveform comparisonbetween Data & Emulated LWLM

Data

LWLM

Amplitude

1400

Time (ms)

2400


Attenuation of wlm
Attenuation of WLM

600

Time

(ms)

2400

0

3175

Offset (m)



Attenuation of wlm2
Attenuation of WLM

600

Time

(ms)

2400

0

3175

Offset (m)



Subtracted wlm
Subtracted WLM

600

Time

(ms)

2400

0

3175

Offset (m)


Outline4
Outline

  • Introduction

  • Theory

  • Synthetic experiments

  • Application to Unocal data

  • Conclusion


Conclusion
Conclusion

  • Theoretically revives Berryhill and Wiggins

  • methods for primary-preserving removal of one

  • kind of water-layer-multiples.

  • Requirements are practically obtainable,

  • and can be derived from seismic data.

  • Applicable to field data with approximations.

  • Overcomes the Delft method by alleviating

  • acquisition requirements and the need to know

  • the source signature.


Future work
Future Work

  • Ghost decomposition for field data.

  • 3D to 2D seismic data conversion.

  • Multiple subtraction.


Reference
Reference

  • Berryhill J.R. and Kim Y.C., 1986, Deep-water pegleg and

  • multiples: emulation and suppression: Geophysics Vol. 51,

  • 2177-2184.

  • Wang Y., 1998, Comparison of multiple attenuation methods

  • with least-squares migration filtering: UTAM 1998 annual

  • report, 311-342.

  • Wiggins J.W., 1988, Attenuation of complex water-multiples

  • by wave-equation-based prediction and subtraction:

  • Geophysics Vol.53 No.12, 1527-1539.


Thanks
Thanks

  • 2003 members of UTAM for financial support.


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