2015 Workplan for “VVAz” Analysis of Prestack Migrated Data Jie Qi and Kurt J. Marfurt (The...

2015 Workplan for “VVAz” Analysis of Prestack Migrated Data

Jie Qi and Kurt J. Marfurt

(The University of Oklahoma)

AASPI

Outline

• Introduction• Motivation• Challenge

• Methodology • VVAz • AVAz• Azimuthal crosscorrelation

• Application• Geology background• Azimuthal attributes

• Conclusion

2

AASPI

Motivation

• Azimuthally limited or vector-tile gathers are part of the wide-azimuth processing workflow

• Can we implement interpretation tools to provide residual AVAz analysis capabilities?

• If the data were migrated using isotropic velocities, these residuals are a measure of VVAz

• The application of such a tool would increase vertical resolution and precondition the data for subsequent AVAz analysis

3

4

Horizontal Transverse Isotropy (HTI) medium

(Left): No HTI anisotropy results in equal travel time paths in all azimuths;

(Right): In an HTI anisotropic media with aligned vertical fractures the travel time is azimuth dependent and is not equal in all directions.

(Courtesy of Close et. al., 2010)

Shear wave spitting in anisotropic medium

5(Courtesy of Ed Garnero)

3-CReceiver

Fracture:

• A key factor in the optimization of reservoir production

• High natural fractures – high production

• Helps to identify sweet spots

• Anisotropic properties: intensity and orientation

• Anisotropy analysis: amplitude and velocity

6(Photos courtesy of Brian Cardott)

Woodford shale Marcellus Shale

Outline

• Introduction• Motivation• Challenge

• Methodology • VVAz • AVAz• Azimuthal crosscorrelation

• Application• Geology background• Azimuthal attributes

• Conclusion

7

AASPI

Velocity vs. Azimuth (VVAz)

• Advantages • Easy to generate azimuthally-binned data• Computation is fast and simple, providing a level of confidence• Requires phase- but not amplitude-preservation

• Disadvantages• Suffers from vertical resolution problems associated with Dix’s equation

8

Amplitude vs. Azimuth (AVAz)

• Advantages • Easy to generate azimuthally-binned data• Computation is fast and simple, providing a level of confidence • Computations are volumetric within the (properly registered) zone of interest

• Disadvantages• Requires amplitude-preserving processing and migration (AVAz)

Velocity variation with angle and azimuth (VVAZ)

9

Vint(φ)=V0+εcos[2(φ- φsym)]

θ

Nφ

Nφsym

If ε is zero, it becomes interval velocity.

φsym

Amplitude vs. Azimuth (AVAz)

(Rueger, 1996)

R(θ,φ)=A+{Biso+Banisocos[2(φ- φsym)]}sin2θ

θ

Nφ

Nφsym

Amplitude vs. Offset (AVO)R(θ,φ)=A+{Biso }sin2θ

Amplitude vs. Azimuth (AVAz)R(θ,φ)=A+{Biso+Banisocos[2(φ- φsym)]}sin2θ

Amplitude vs. Offset (AVO)R(θ,φ)=A+{Biso }sin2θ

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Workflows

Conventional VVAz:• Generate long-offset sectors or ’tiles’ at different azimuths φ (unmigrated)• At discrete picked horizons, compute VRMS as a function of azimuth, φ

• Compute interval velocities Vint(φ) using Dix’s equation

• Fit a sinusoidal curve to Vint(φ) to obtain the magnitude and azimuth of anisotropy

AVAz:• Generate long-offset sectors or ’tiles’ at different azimuths φ (migrated)• Pick discrete upper and lower horizons and generate either flattened or stratal

slices throughout the volumetric zone of interest• At every time or depth sample, fit a sinusoid to the amplitude as a function of

azimuth φ

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12

Residual “VVAz” Workflow

Shot gathers

PrestackTime

migration

Azim 1 gathers

Azim 8 gathers

……Azim 2 gathers

AVAz anisotropyBaniso, ψaniso

Migrated gathers

Dynamic alignment

VVAz Anisotropy

Structure oriented filter

Dynamic alignment

Dynamic alignment• Correlate adjacent azimuths

• Find ∆τ and value of highest correlation coefficient• Autocorrelate & crosscorrelate

13

……

Azim 1 Azim 2 Azim 8Time

(Modified from Roende et al., 2008) 14

Vint(φ)=V0+εcos[2(φ- φsym)]

Azimuth, φ

V 0+εc

os[2

(φ- φ

sym

)]

ε iso

ε anisoφsy

m

V0

V0 + ε

V0 - ε

Dynamic alignment

• Least-squares fit ∆τ to find εaniso and φsym

15

Isotropic Layer 1

Anisotropic Layer 2

Dynamic alignment

Dynamicalignment

Isotropic Layer 1

Anisotropic Layer 2

High anisotropy

Azimuthal data

Aligned data

• Stretch and squeeze data to provide flattened events

εaniso and φsym

Isotropic Layer 1

Anisotropic Layer 2

Outline

• Introduction• Motivation• Challenge

• Methodology • VVAz • AVAz• Azimuthal crosscorrelation

• Application• Geology background• Azimuthal attributes

• Conclusion

16

AASPI

Ellenburger

Marble Falls

Stratigraphic Cross Section

(Modified from Pollastro et al., 2009)

Unconformity

17

Stacked azimuth sector gathersAnisotropy indicators

Data aligned Data Misaligned(Roende et al., 2008)

CMP398

CMP399

CMP400

Tim

e (s

)

0.8

0.7

0.6

0.5

CMP no.

18

Amplitude as a function of azimuth (AVAz)

~3500 ft

0.6

0.8

~8 ms

Tim

e (s

)

0.7

stro

nge

r

weake

r

(Roende et al., 2008) 19

AVAz products

Low High 1 mile

Tim

e (s

)

0.4

1.0 Intercept, A

Isotropic gradient, Biso

Tim

e (s

)

0.4

1.0

Anisotropic gradient, Baniso

Tim

e (s

)

0.4

1.0

(Modified from Roende et al., 2008) 20

Top Marble Fall

Top Ellenburger

Outline

• Introduction• Motivation• Challenge

• Methodology • VVAz • AVAz• Azimuthal crosscorrelation

• Conclusion

21

AASPI

Anticipated Challenges

• Will there be a clear correlation between AVAz and VVAz?

• Can the residuals be computed gather by gather, or will layer-stripping become important?

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Acknowledgements

• Marathon Oil Co. for a license to their survey

• Sponsors of the AASPI consortium for financial support and

technical encouragement

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AASPI