AVO analysis and Impedance Inversion Okey Ileka 1

AVO analysis and Impedance
Inversion
Okey Ileka
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AVO Analysis
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Introduction
AVO Pre-processing
AVO modeling
AVO parameters
AVO crossplot analysis
AVO attributes
Some application of AVO
Probabilistic AVO analysis
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Impedance Inversion
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Post stack 1D Impedance Inversion
Far-offset elastic Impedance
Lambda-mu-rho estimation
P to S elastic Inversion
Anisotropic elastic Impedance
Interpretation of Rock physics template
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Introduction
• AVO is the amplitude variation with offset
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Introduction
Castagna lecture notes
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Introduction
Castagna lecture notes
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Simplified Shuey (1985) Form of
the Richards and Frazier (1976)
Approximation
R(θ ) ≈ A + B sin θ
2
A = Rp
B ≈ R p − 2 Rs
1 ⎛⎜ ΔV p Δρ ⎞⎟
A≈
+
⎜
2 ⎝ Vp
ρ ⎟⎠
Vs Δρ 1 ΔV p
Vs ΔVs
B ≈ −2 2
+
−4 2
Vp ρ 2 Vp
V p 7 Vs
2
2
Third Order Approximation
R(θ ) ≈ A + B sin θ + C sin θ tan θ
2
1 ⎛⎜ ΔV p Δρ ⎞⎟
A=
+
2 ⎜⎝ V p
ρ ⎟⎠
2
2
1 ΔV p
C≈
2 Vp
1 Δρ
A−C ≈
2 ρ
Castagna lecture note
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Hiltermann Approximation
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474
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2
2
R(θ ) ≈ A cos θ + 2.25Δσ sin θ
G
G = A+ B
Castagna lecture note
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AVO preprocessing
Castagna lecture notes
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Castagna lecture note
Factors that amplitudes
• Earth effects
• Acquisition related effects
• Noise
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Earth effects
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Spherical divergence
Absorption
Transmission losses
Interbed multiples
Converted phases
Tunning effect
Anisotropy
structure
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Acquisition-related effects and
noise
• Acquisition-related effects
• Source reciever arrays
• Reciever sensitivity
• Noise
• Source generated noise
• Coherent or random noise
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AVO Pre-processing
• Spiking deconvolution and wavelet
processing
• Spherical divergence correction
• Surface consistent amplitude balancing
• Multiple removal
• NMO correction
• DMO correction
• Pre-stack migration
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AVO preprocesing
Castagna lecture notes
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Castagna lecture notes
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AVO modeling
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Physical Interpretation
R (θ ) ≈ A + B sin θ
2
Castagna lecture notes
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(Russel, 1999)
AVO parameters
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Castagna lecture notes
AVO crossplot
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From Simm et al., 2000
Castagna lecture notes
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AVO attributes
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AVO Indicators/Attributes
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Intercept
Gradient
Near and far stacks
Curvature
CDP stack
Change in Poisson’s ratio
Fluid Factor
Castagna lecture notes
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Intercept minus Gradient
Intercept plus Gradient
Intercept times Gradient
Rp-Rs
P and S wave velocity
contrast
• Density Contrast
• Amoco Indicator F(F-N)
• Lamba-mu-rho
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Calculated AVO Attributes
A = intercept
B = gradient
r² = correlation
A×B
(A + B)/2 ~ Rp - Rs
(A – B)/2 ~ Rs
A = intercept
B = gradient
C = curvature
r² = correlation
A×B
(A + B)/2 ~ Rp - Rs
(A – B)/2 ~ Rs
A–C
NI = normal intercept
PR = Poisson reflectivity
r² = correlation
NI × PR
Castagna lecture notes
Shuey 2 Term
RC (θ) = A + B (sin²θ)
Shuey 3 Term
RC (θ) = A + B (sin²θ) + C (sin²θ)(tan²θ)
Verm-Hilterman
RC (θ) = NI(cos²θ) + PR(sin²θ)
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Roden, 2005
Some application of AVO
• Residual gas saturation (converted waves)
• Flat spot analysis
• Overpressure detection
• Density estimation
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Probabilistic AVO analysis
• In probabilistic AVO analysis the AVO
parameters and attributes are assigned
probability density function (PDF) or
cumulative density function (CDF)
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Impedance Inversion
• The goal of geophysical inversion is to
estimate model parameter from observed
data
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Impedance Inversion
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•
•
•
•
•
Post stack 1D Impedance Inversion
Far-offset elastic Impedance
Lambda-mu-rho estimation
P to S elastic Inversion
Anisotropic elastic Impedance
Interpretation of Rock physics template
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Poststack 1D impedance Inversion
• Inversion of near stack traces
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Acoustic Impedance
Inversion
Near
Angle Stack
Sonic,Density
Logs
tie
Wavelet
tie
Bandlimited
Inversion
Horizons
AI Earth
Model
Trend
Model
Merged
AI
Castagna lecture note
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Sena, 1997
Far offset elastic Impedance
• Inversion of far offset traces
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The Elastic Impedance
E = Vpα Vsβ ργ
α = 1/cos2θ
β = -8(Vs/Vp)2sin2θ
γ = 1 + β/2
Castagna lecture notes
Sena, 1997
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Elastic Impedance Inversion
Far
Angle Stack
Sonic,Shear Sonic
and Density Logs
tie
Wavelet
tie
Bandlimited
Inversion
Horizons
EI Earth
Model
Trend
Model
Merged
EI
Castagna lecture note
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Sena, 1997
Lambda Rho estimation
Hilterman’s lecture note
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P –to- S elastic Inversion
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Reflection Coefficients: Angle vs.
Offset
σ
σ
σ
σ
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Stewart and Gasier lecture note
P-S Reflection Coefficient
(Aki & Richards, 1980)
Rps
First Order
Relative S-velocity change
Stewart and Gasier lecture note
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Relative density change
Anisotropic elastic Inversion
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Anisotropy
Hilterman course notes
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Anisotropic Inversion
Hilterman course notes
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Interpretation of Rock Physics
Template
• The rock physics template is based on a
compiled catalog or atlas of RPT’s
calculated by a rock physics expert.
• The seismic interpreter can interpret
elastic inversion results without in-depth
knowledge about rock physics theory
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• Thank you
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