2015 workplan for “vvaz” analysis of prestack migrated data jie qi and kurt j. marfurt (the...
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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
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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
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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
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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
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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)
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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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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
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……
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
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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
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AASPI
Ellenburger
Marble Falls
Stratigraphic Cross Section
(Modified from Pollastro et al., 2009)
Unconformity
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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.
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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