wavefield prediction of water-layer-multiples

WAVEFIELD PREDICTION OF WAVEFIELD PREDICTION OF WATER-LAYER-MULTIPLESWATER-LAYER-MULTIPLES

Ruiqing HeRuiqing He

University of UtahUniversity of Utah

Feb. 2004Feb. 2004

OutlineOutline

• IntroductionIntroduction

• TheoryTheory

• Synthetic experimentsSynthetic experiments

• Application to Unocal dataApplication to Unocal data

• ConclusionConclusion

IntroductionIntroduction

• Primary-preserving multiple removal demands Primary-preserving multiple removal demands

accurate wavefield prediction of multiples. accurate wavefield prediction of multiples. • Other works:Other works:

- Delft- Delft

- Amundsen, Ikelle, Weglein, etc.- Amundsen, Ikelle, Weglein, etc.

• Water layer multiplesWater layer multiples

OutlineOutline

• IntroductionIntroduction

• TheoryTheory

• Synthetic experimentsSynthetic experiments

• Application to Unocal dataApplication to Unocal data

• ConclusionConclusion

Berryhill and Wiggins’s MethodsBerryhill and Wiggins’s Methods

Off-shoreOff-shoreseismic dataseismic data

MultipleMultipleattenuationattenuation

Filtered SubtractionFiltered Subtraction

Water surface

Water bottom

Receiver line

Kirchhoff SummationKirchhoff SummationForward extrapolate tracesdown to water bottom

Kirchhoff SummationKirchhoff Summation

Forward extrapolate bottom traces up to receivers Emulated Muliples

The proposed methodThe proposed method

Off-shoreOff-shoreseismic dataseismic data

Wave forwardWave forwardextrapolation extrapolation

to the water bottomto the water bottom

Wave forwardWave forwardextrapolation extrapolation

to the receiversto the receivers

Other multipleOther multipleattenuationattenuation

filteringfiltering

Decomposition Decomposition of of

receiver-sidereceiver-sideghostsghosts

FDFD FDFD

FDFD

Multiples Multiples with last with last

round-trip round-trip in water layerin water layer

Primary-Primary-preservingpreserving

multiplemultipleremovalremoval

FD: Finite DifferenceFD: Finite Difference

DS: Direct (simple) SubtractionDS: Direct (simple) Subtraction

DSDS

Why Finite Difference?Why Finite Difference?

• AdvantageAdvantage

- speed- speed

- convenience- convenience

- capability: heterogeneous medium- capability: heterogeneous medium

• DisadvantageDisadvantage

- dispersion?: reality, high-order FD- dispersion?: reality, high-order FD

Types of Water-Layer-MultiplesTypes of Water-Layer-Multiples• LWLM: Multiples that have the last round-trip in the water layer.LWLM: Multiples that have the last round-trip in the water layer.• Other WLM: other water-layer-multiples except LWLM.Other WLM: other water-layer-multiples except LWLM.

Wavefield Extrapolation of RSGWavefield Extrapolation of RSG

Water surface

Receiver line

Mirror image ofthe Receiver line

UU RSGRSG

RSGRSG

i

iii

iii FttUr

txtRSG )*)((cos

1)(

iir

Decomposition of RSGDecomposition of RSG

UU

i

ii ttUftRSG ))(()(

RSGRSG

ff

++++ DATADATA

Water surface

Receiver line

Mirror image ofthe Receiver line

OutlineOutline

• IntroductionIntroduction

• TheoryTheory

• Synthetic experimentsSynthetic experiments

• Application to Unocal dataApplication to Unocal data

• ConclusionConclusion

Synthetic ModelSynthetic Model

DepthDepth (m)(m)

00

15001500

Offset (m)Offset (m)00 32503250

waterwater

SandstoneSandstone

Salt domeSalt dome

BSRBSR

Synthetic seismic dataSynthetic seismic data

TimeTime (ms)(ms)

400400

25002500

Offset (m)Offset (m)00 32503250

Decomposed RSGDecomposed RSG

TimeTime (ms)(ms)

400400

25002500

Offset (m)Offset (m)00 32503250

Predicted LWLMPredicted LWLM

TimeTime (ms)(ms)

400400

25002500

Offset (m)Offset (m)00 32503250

Waveform ComparisonWaveform Comparisonbetween Data & RSG between Data & RSG

Am

pli

tud

eA

mp

litu

de

Time (ms)Time (ms)600600 24002400

DataData

RSGRSG

Waveform ComparisonWaveform Comparisonbetween Data & LWLM between Data & LWLM

Am

pli

tud

eA

mp

litu

de

Time (ms)Time (ms)600600 24002400

DataData

LWLMLWLM

Waveform ComparisonWaveform Comparisonbetween Data & RSG+LWLM between Data & RSG+LWLM

Am

pli

tud

eA

mp

litu

de

Time (ms)Time (ms)600600 24002400

DataData

RSG + LWLMRSG + LWLM

Elimination of RSG & LWLMElimination of RSG & LWLM

TimeTime (ms)(ms)

400400

25002500

Offset (m)Offset (m)00 32503250

Further Multiple AttenuationFurther Multiple Attenuation

TimeTime (ms)(ms)

400400

25002500

Offset (m)Offset (m)00 32503250

OutlineOutline

• IntroductionIntroduction

• TheoryTheory

• Synthetic experimentsSynthetic experiments

• Application to Unocal dataApplication to Unocal data

• ConclusionConclusion

Unocal field dataUnocal field data

TimeTime (ms)(ms)

600600

24002400

Offset (m)Offset (m)00 31753175

Inadequate RSG DecompositionInadequate RSG Decomposition

TimeTime (ms)(ms)

600600

24002400

Offset (m)Offset (m)00 31753175

Emulated LWLMEmulated LWLM

TimeTime (ms)(ms)

600600

24002400

Offset (m)Offset (m)00 31753175

Waveform comparisonWaveform comparisonbetween Data & Emulated LWLMbetween Data & Emulated LWLM

Am

pli

tud

Am

pli

tud

ee

Time (ms)Time (ms)14001400 24002400

DataData

LWLMLWLM

Attenuation of WLMAttenuation of WLM

TimeTime (ms)(ms)

600600

24002400

Offset (m)Offset (m)00 31753175

Attenuation of WLMAttenuation of WLM

Attenuation of WLMAttenuation of WLM

TimeTime (ms)(ms)

600600

24002400

Offset (m)Offset (m)00 31753175

Attenuation of WLMAttenuation of WLM

Subtracted WLMSubtracted WLM

TimeTime (ms)(ms)

600600

24002400

Offset (m)Offset (m)00 31753175

OutlineOutline

• IntroductionIntroduction

• TheoryTheory

• Synthetic experimentsSynthetic experiments

• Application to Unocal dataApplication to Unocal data

• ConclusionConclusion

ConclusionConclusion• Theoretically revives Berryhill and Wiggins Theoretically revives Berryhill and Wiggins methods for primary-preserving removal of one methods for primary-preserving removal of one kind of water-layer-multiples.kind of water-layer-multiples.

• Requirements are practically obtainable,Requirements are practically obtainable, and can be derived from seismic data.and can be derived from seismic data.

• Applicable to field data with approximations.Applicable to field data with approximations.

• Overcomes the Delft method by alleviating Overcomes the Delft method by alleviating acquisition requirements and the need to knowacquisition requirements and the need to know the source signature.the source signature.

Future WorkFuture Work

• Ghost decomposition for field data.Ghost decomposition for field data.

• 3D to 2D seismic data conversion.3D to 2D seismic data conversion.

• Multiple subtraction.Multiple subtraction.

ReferenceReference

1.1. Berryhill J.R. and Kim Y.C., 1986, Deep-water pegleg and Berryhill J.R. and Kim Y.C., 1986, Deep-water pegleg and multiples: emulation and suppression: Geophysics Vol. 51, multiples: emulation and suppression: Geophysics Vol. 51, 2177-2184.2177-2184.2.2. Wang Y., 1998, Comparison of multiple attenuation methods Wang Y., 1998, Comparison of multiple attenuation methods with least-squares migration filtering: UTAM 1998 annual with least-squares migration filtering: UTAM 1998 annual report, 311-342. report, 311-342. 2.2. Wiggins J.W., 1988, Attenuation of complex water-multiples Wiggins J.W., 1988, Attenuation of complex water-multiples by wave-equation-based prediction and subtraction: by wave-equation-based prediction and subtraction: Geophysics Vol.53 No.12, 1527-1539.Geophysics Vol.53 No.12, 1527-1539.

ThanksThanks

• 2003 members of UTAM for financial 2003 members of UTAM for financial support.support.