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AVO Modeling for the Effects of Attenuation and Random Scattering Using Thin-Slab Propagator. *. Xian-Yun Wu & Ru-Shan Wu. Modeling and Imaging Lab. University of California, Santa Cruz. * Presently at URC, ExxonMobil. Outline. Introduction. Dual-domain one-way thin-slab propagator. - PowerPoint PPT Presentation
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AVO Modelingfor the Effects of Attenuation and Random
Scattering Using Thin-Slab Propagator
Xian-Yun Wu & Ru-Shan Wu
Modeling and Imaging Lab.University of California, Santa Cruz
Presently at URC, ExxonMobil
Outline
Introduction
Effects of scattering Effect of attenuation AVO in heterogeneous visco-elastic media Frequency-Dependent AVOs
Conclusions
Dual-domain one-way thin-slab propagator
Numerical examples
AVO analysis (elastic parameters and fluid contents)
Introduction
Significant effects of wave propagation on local true-amplitude (scattering, anelasticity, frequency-dependent, etc.)
Developing efficient AVO forward modeling tools (high efficiency, complicated models)
Dual-domain one-way thin-slab propagator and its applications
Dual-domain one-way propagator (thin-slab)
)(ku x0P
)(ku x0S
X-domain
K-domain
0S
Δzik ueSz
0P
Δzik uePz
Up
Us
0Pu
0Su
0Pu
0Su
0
0
0
elastic
0S
Δzik ueSz
0P
Δzik uePz Up
Us
+
+
updated fieldIncident
field
(x)u(x)u)( f
βfα
SPPPxik
ρ
xδρdxe x
:ˆˆ1
2
kkikμλ
xδλdxe PPxikx
(x)u
)( fα
(x)ε(x)ε
1
2
)(2 fβ
fα
SPPPxik
ikμλ
xδμdxe x
Scattered field (P wave):
Elastic thin-slab propagator
kx
dxe SSPSxikx ˆ(x)u(x)u)( f
βfα
(x)ε(x)ε
1
2
)(2 fβ
fα
SSPSxik
ik
xdxe x
Scattered field :
Elastic thin-slab propagator
Incorporate Q factors into the propagator
),2/1( , )2/1( Sp QiQi ),2/1( , )2/1( 0
000
00 SP QiQi
Complex velocities :
Elastic parameters :
0)()( xx; )()( 0 xx 0)()( xx
222 2 ; 2 2000
200
2000 2 ; 2
Perturbations :
Effects of scattering (heterogeneities)
Effect of attenuation (intrinsicity)
AVO in heterogeneous visco-elastic media
Frequency-dependent AVO
Numerical examples
Effects of scattering due to heterogeneities in elastic parameters
Type: exponential function Corrl. lengths: 100m in x and 40m in z.The rms: 2%
Plane P-wave
Homogeneous Random
Transmitted wavefront
Thin-slab
FD
Reflection amplitudes in random media
Exponential
Reflection amplitudes in random media
White-noise
Qp=Qs=50
Qp=Qs=500
Effects of attenuation
Reflection amplitudes in anelastic random media
Reflection amplitude in elastic random media
Reflection amplitudes in random media with Q
AVO in anelastic and random media
1/Q ~ frequency
Frequency-dependent AVO
shale
oil sand
*S R
Conclusions
Properties of target zones control the AVO trends; Qs mainly affect the absolute amplitudes of reflections; scatterings mainly increases local variations in reflected amplitudes.
Spatially correlated heterogeneities (even as weak as rms=1%) may produce significant effects on AVO.
In visco-elastic heterogeneous media, local reflections may be the result of interaction between Q and elastic parameters.
Table 1. Reservoir model
shale 3170 1668 2.36 0.31
gas 3350 2231 2.02 0.10Oil 3527 2131 2.22 0.21brine 3551 2109 2.27 0.23
Note: Parameters are taken from Simmons and Backus (1994).