the importance of prestack seismic massive · pdf fileforce seminar - 06/02/02. prestack data....

FORCE seminar - 06/02/02. Prestack Data. NPD Stavanger.

Philippe JULIEN - Massive modelling and AVO

FORCE: Prestack Data - The key to modern interpretation

THE IMPORTANCE OF PRESTACK SEISMIC

MASSIVE MODELLING FOR A.V.O. CALIBRATION AND

SEISMIC RESERVOIR CHARACTERIZATION

Authors: Ph. Julien (speaker), F. Pivot Acknowledgements: A. Douillard, J. Marrauld, C. Borghi



INTRODUCTION

* Seismic reservoir characterization more andmore uses prestack data.

* We will focus on the A.V.O. (Amplitude VersusOffset) calibration & prediction.



Now

ComputeComputeseismicseismic

attributesattributes

ComputeComputeseismicseismic

attributesattributes

CalibrationCalibration??

3Dseismic data

3Dreservoir prop.

nDseismic data

3Dreservoir prop.

Before...

The calibration problem in seismic reservoir characterizationThe calibration problem in seismic reservoir characterization

CalibrationCalibration?????????????? 3D

uncertainties.



OVERVIEW of QUESTIONS in the frame of the LITHOSEISMIC project

SEISMIC WORLDSEISMIC WORLD

GEOLOGICAL WORLDGEOLOGICAL WORLD

* What is the sensitivity of the seismic* What is the sensitivity of the seismicresponse for a given geological variation?response for a given geological variation?

* Which geological property can be * Which geological property can be mapped with seismic (and which onemapped with seismic (and which one can not) ? can not) ?

* Which seismic attributes for* Which seismic attributes for solving a geological problem? solving a geological problem? * Which geological constraints must be* Which geological constraints must beadded?added? * Is the seismic response unique?* Is the seismic response unique?

* Which uncertainties* Which uncertainties??

(tectonics, sedimentology, petrophysics)

==>3 steps approach



WHY SO MANY AVO FAILURES?

A.V.O is an efficient method for fluidscharacterization… but too many failures in the past.

1) AVO depends on fluids (and their saturations).





2) But AVO also depends on:

* lithology Ex.: - coal layers; - Vclay.





2) But AVO also depends on:

* lithology: Ex.: - coal layers; - Vclay.

* reservoir thickness: Ideally, AVO is reliable forreservoirs with a thickness larger than the tuningthickness.

Note: Amplitudes depend on porosity.



IMPLICATIONS

* AVO inversion does not lead (in general) to a uniquesolution.



IMPLICATIONS

* AVO inversion does not lead (in general) to a uniquesolution.

* Usually, some seismic modelling (~ 10 modellingexperiments) is carried out to understand the AVOphenomenom.

* This is not enough: hundreds of seismic modellingexperiments are mandatory to begin understandingthe seismic response…



AVO analysis with massive seismic AVO analysis with massive seismic modellingmodellingEXAMPLE OF APPLICATIONEXAMPLE OF APPLICATION Example : Post-Mortem StudyExample : Post-Mortem Study

All models with phi below 20%,No tuning (overburden shale layer and reservoir >150 m)

Gas(Sw20/60%)

Brine

• Fluid discrimination difficult as brine case (phi=10%) is very similar to gas response (phi=15%). May be possible on long offsets.

Impact of fluid content on AVO effectImpact of fluid content on AVO effect



MASSIVE SEISMIC MODELLING: a mandatory step

* Hundreds of seismic modelling experiments aremandatory to begin understanding the seismicresponse…

* References: - O. Youn (Unocal) & H. Zhou (Exxon), SEG 98; - F. Pivot et al. (TotalFinaElf), EAGE 99; - F. Pivot & O. Balz (TotalFinaElf), EAGE 00; - Y. El Ouair & F. Pivot (TotalFinaElf), SEG 01.

* Such calibration & modelling stages will have an impact onseismic acquisition, processing and interpretation.



OVERVIEW OF THE PRESENTATION

I) A few recalls: Petro-elastic modelling, amplitudecalibration and 1D seismic massive modelling.

II) Application: A real data example: impact onacquisition, processing and interpretation.

III) 2D or 3D perturbations: Real examples; impacts onthe interpretation.



A.V.O. CALIBRATION: the general processA.V.O. CALIBRATION: the general process

GoalCalibration: to find a relationship between well and seismic data.Prediction: to extrapolate this relationship to the whole seismic cubes.

PETRO-ELASTIC MODELLING, AMPLITUDE CALIBRATIONand MASSIVE PRESTACK MODELLING.

Petrophysical measurements

Elastic measurements/logs

1:Petro-elastic modellingSurface seismics

Well seismics

2: Amplitude calibration

(Massive) prestack models

2/3:Seismic modelling 4:Impacts



Synergy for calibration: the petro-elastic model (1st step)AmplitudesAmplitudes

DensityDensityP SonicP Sonic

AVOAVO

S SonicS Sonic

CoresCores

LogsLogs

SedimentologySedimentology

PetroPetro-elastic-elasticModelModel

PETROPHYSICAL PARAM.E

LA

STIC

PA

RA

M.



Second step: AVO CALIBRATIONMULTI-TIE & AVA TIE

NEAR FARw

ater

gas

IP POISSON GR Log VSP Seis south east north west Walkaway

Log Seis south east north west Walkaway

MU

LTI-T

IEA

VA T

IE

Surface seismic coherentwith walkaway

AM

PLIT

UD

E

ANGLE (°)

ANALYSIS AT 2132 ms

logsurface seismic

walkaway southwalkaway northwalkaway eastwalkaway west



GENERALGENERAL CONCEPT OF MASSIVE MODELLING (3rd step)CONCEPT OF MASSIVE MODELLING (3rd step)

Petro & Structuralperturbations

Inputmodel

ρρρρ,Vp,Vs Pert. blockymodels

(ρρρρ,Vp,Vs)new triplets

Seismicprestack PP or PS

modelling

Seismic CMPgathers



THE MODELLING TECHNIQUESTHE MODELLING TECHNIQUES

Details on the 3 modelling algorithms

Reflectivity calculation + Zoeppritz: fast and easy.Can not deal with tuning.Can not deal with internal multiples, complex interference patterns, attenuation.

Ray tracing + Zoeppritz:fast and more precise.Can deal with tuning.Can not deal with internal multiples , complex interference patterns, attenuation.

Wave-equation:Slow but more preciseCan deal with tuningCan deal with internal multiples, wave conversion modes, Q attenuation,...




I) A few recalls: Petro-elastic modelling, amplitudecalibration and seismic massive modelling approach.


III) 2D extension: the approach, a real case, impact onthe interpretation.



1

2

5

9

13

Ocean water

Background

Transition zone

Transition zone

Transition zone

Sand A

Sand B

Sand C

Surrounding shale

General geometry of the reservoir model

Perturbations:For each sand separately

PHI: 10% -> 30% step 5%Sw: 20% to 100% step 40%Vclay: 5% to 35% step 10%thick: 5m to 40m step 5m

choosing only models such asPHI / (1-Vclay) <=0.4 (petrophy. condition)

TOTAL for each sand: 792 models

TOTAL number of models:2376

AVO ANALYSIS OF POSSIBLE RESERVOIRS



Impact of parameters on AVO response of sands

Water saturation increasing

Porosity increasing

« Vclay increasing »

Near

Far

Near

Farthickness

increasing

Water line

SUMMARY OF THE STUDY

A geological input is necessary.

Arrows indicate impact of modfying eachparameter on the AVO near-far response.

Porosity has a huge impact on amplitudes.Sw and Vclay have an impact on AVO.

Modifying (PHI and Sw) can leadto the same seismic responseas modifying Vclay.



elastic 1

elas

tic 2

2

PetrophyPetrophy. X. XSeismic att. 1

Seis

mic

att.

2PetrophyPetrophy. X. X

Seismic att. 1

Seis

mic

att.

2

PetrophyPetrophy. X. X

UPSCALING

3rd action: seismic

2nd action: model

1st action: well INCREASE OF UNCERTAINTIES

Main methodology for Seismic Reservoir Characterization



IMPORTANCE OF STATISTICAL CALIBRATION

AVO calibration & seismic modelling have an impact on: 1) Seismic acquisition: * maximum offset ==> de-multiple techniques,

* necessary seismic resolution (i.e. freq. content), * acquisition foot-print reduction,…



AVO analysis with massive seismic AVO analysis with massive seismic modellingmodellingEXAMPLE OF APPLICATIONEXAMPLE OF APPLICATION Example : Post-Mortem StudyExample : Post-Mortem Study

All models with phi below 20%,No tuning (overburden shale layer and reservoir >150 m)

Gas(Sw20/60%)

Brine

• Fluid discrimination difficult as brine case (phi=10%) is very similar to gas response (phi=15%). May be possible on long offsets.

Impact of fluid contentImpact of fluid content




AVO calibration & modelling have an impact on: 1) Seismic acquisition: * maximum offset ==> de-multiple techniques,

* necessary seismic resolution (i.e. freq. content), * foot-print reduction,…

2) Seismic processing: * choice of the useful offset ranges, * reliability of amplitudes and Signal/Noise ratio

improvement, * full-wave modelling shows how seismic wave

propagation (multiples, converted waves, refractions,…)does [not] disturb amplitude analysis.




AVO calibration & modelling have an impact on: 1) Seismic acquisition: * maximum offset ==> multiple removal,

* necessary seismic resolution (i.e. freq. content), * acquisition foot-print reduction,… 2) Seismic processing: * choice of the useful offset ranges, * reliability of amplitudes and Signal/Noise ratio improvement,… * impact on amplitudes of seismic wave propagation.

3) Seismic interpretation: * ranking of petrophysical parameters, * building a list of possible AVO cases (==> What are

the best seismic attributes?), * quantitative interp. & uncertainties eval. & reduction, * seismic monitoring: impact of pressure &

saturation,...




I) A few recalls: Petro-elastic modelling, AVO calibration,and 1D seismic massive modelling approach.


III) 2D or 3D (1.5 D) perturbations: the approach andexemples: impact on the interpretation.



SIMPLE APPLICATION ON A REAL DATA EXAMPLE

Create prestack synthetic images from geological facies interpretation

Two possible fluid scenarii:- water- light oil



SIMPLE APPLICATION ON A REAL DATA EXAMPLE - Synthetic versus real : analyse differences and similarities

LIGHT OIL CASE



SIMPLE APPLICATION ON A REAL DATA EXAMPLE

Synthetic versus real : analyse differences and similarities

WATER CASE



MODELING OF PERTURBED PETROPHYSICAL AND STRUCTURAL SCENARII MODELING OF PERTURBED PETROPHYSICAL AND STRUCTURAL SCENARII Description of the initial model and perturbations from X wells.

Water

Overburden

Layer A

ReservoirLayer BLayer C

Basement

Sw: 25 - 55 % dSW: 10 %Porosity: 18 -30 % dpor: 4%Structure:

✔ Overburden: constant (fromseabottom)

✔ Layer A(shale): 5-20 m delta 5m✔ Reservoir (Gas): 9 m -29 m delta:

5m✔ Layer C.: 0.2 - 50.2 m delta: 25 m

960 perturbations

Application on dataset

Seismic modeling of synthetic CMP gathers...Seismic modeling of synthetic CMP gathers...



Classification of real seismic data using post-stack synthetic wavelets.

Gas ThicknessGas Thickness Porosity MapPorosity Map




Well 1Well 1

Gas: Gas: measured: 14 m measured: 14 m predicted: 13.2 m predicted: 13.2 m

Porosity: Porosity: measured: 24%-29% measured: 24%-29% predicted: 29.5% predicted: 29.5%

Well 2Well 2


Porosity: Porosity: measured: 23%-28% measured: 23%-28% predicted: 26.1 % predicted: 26.1 %

Well 3Well 3


Porosity: Porosity: measured: 28%-30% measured: 28%-30% predicted: 26.0 % predicted: 26.0 %

PREDICTION OF RESERVOIR PROPERTIES AT WELL LOCATIONSPREDICTION OF RESERVOIR PROPERTIES AT WELL LOCATIONS




CONCLUSION

1) For many years, structural calibration has beenmainly highlighted. AVO calibration is a mandatoryprocess.

2) The AVO phenomenom is very complex: the solutionis generally not unique.AVO calibration (including petro-elastic modelling &massive seismic modelling) allows to understand whyso many dry wells have been drilled, using AVO.



CONCLUSION

3) We propose a methodology which goes beyond theconventional calibration:

- to identify the seismic response of a geologicalhypothesis: to be more predictive,

- to test different scenarii ==> uncertainties reduction, - to look at the impact on acquisition, processing and

interpretation.

4) We already knew that seismic calibration was onemeeting point between geologists & geophysicists.

Amplitudes calibration (broadly speaking) is ameeting point in geosciences

the importance of prestack seismic massive · pdf fileforce seminar - 06/02/02. prestack data....

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