Converted-wave amplitude versus offset (AVO) behavior may be fit with
a cubic relationship between reflection coefficient and ray parameter.
Attributes extracted using this form can be directly related to elastic
parameters with low-contrast or high-contrast approximations to the
Zoeppritz equations. The high-contrast approximation has the advantage
of greater accuracy; the low-contrast approximation is analytically
simpler. The two coefficients of the low-contrast approximation are
a function of the average ratio of compressional-to-shear-wave velocity
(alpha/beta) and the fractional changes in S-wave velocity and density
(Deltabeta/beta and Deltarho/rho). Because of its simplicity, the
low-contrast approximation is subject to errors, particularly for
large positive contrasts in P-wave velocity associated with negative
contrasts in S-wave velocity. However, for incidence angles up to
40 deg and models confined to Deltabeta/beta < 0.25, the errors in
both coefficients are relatively small. Converted-wave AVO crossplotting
of the coefficients of the low-contrast approximation is a useful
interpretation technique. The background trend in this case has a
negative slope and an intercept proportional to the alpha/beta ratio
and the fractional change in S-wave velocity. For constant alpha/beta
ratio, an attribute trace formed by the weighted sum of the coefficients
of the low-contrast approximation provides useful estimates of the
fractional change in S-wave velocity and density. Using synthetic
examples, we investigate the sensitivity of these parameters to random
noise. Integrated P-wave and converted-wave analysis may improve
estimation of rock properties by combining extracted attributes to
yield fractional contrasts in P-wave and S-wave velocities and density.
Together, these parameters may provide improved direct hydrocarbon
indication and can potentially be used to identify anomalies caused
by low gas saturations.
%0 Journal Article
%1 ramos_castagna:2001
%A Ramos, Antonio C. B.
%A Castagna, John P.
%D 2001
%I SEG
%J Geophysics
%K geophysics seismics
%N 6
%P 1721--1734
%R 10.1190/1.1487114
%T Useful approximations for converted-wave AVO
%U http://dx.doi.org/10.1190/1.1487114
%V 66
%X Converted-wave amplitude versus offset (AVO) behavior may be fit with
a cubic relationship between reflection coefficient and ray parameter.
Attributes extracted using this form can be directly related to elastic
parameters with low-contrast or high-contrast approximations to the
Zoeppritz equations. The high-contrast approximation has the advantage
of greater accuracy; the low-contrast approximation is analytically
simpler. The two coefficients of the low-contrast approximation are
a function of the average ratio of compressional-to-shear-wave velocity
(alpha/beta) and the fractional changes in S-wave velocity and density
(Deltabeta/beta and Deltarho/rho). Because of its simplicity, the
low-contrast approximation is subject to errors, particularly for
large positive contrasts in P-wave velocity associated with negative
contrasts in S-wave velocity. However, for incidence angles up to
40 deg and models confined to Deltabeta/beta < 0.25, the errors in
both coefficients are relatively small. Converted-wave AVO crossplotting
of the coefficients of the low-contrast approximation is a useful
interpretation technique. The background trend in this case has a
negative slope and an intercept proportional to the alpha/beta ratio
and the fractional change in S-wave velocity. For constant alpha/beta
ratio, an attribute trace formed by the weighted sum of the coefficients
of the low-contrast approximation provides useful estimates of the
fractional change in S-wave velocity and density. Using synthetic
examples, we investigate the sensitivity of these parameters to random
noise. Integrated P-wave and converted-wave analysis may improve
estimation of rock properties by combining extracted attributes to
yield fractional contrasts in P-wave and S-wave velocities and density.
Together, these parameters may provide improved direct hydrocarbon
indication and can potentially be used to identify anomalies caused
by low gas saturations.
@article{ramos_castagna:2001,
abstract = {Converted-wave amplitude versus offset (AVO) behavior may be fit with
a cubic relationship between reflection coefficient and ray parameter.
Attributes extracted using this form can be directly related to elastic
parameters with low-contrast or high-contrast approximations to the
Zoeppritz equations. The high-contrast approximation has the advantage
of greater accuracy; the low-contrast approximation is analytically
simpler. The two coefficients of the low-contrast approximation are
a function of the average ratio of compressional-to-shear-wave velocity
(alpha/beta) and the fractional changes in S-wave velocity and density
(Deltabeta/beta and Deltarho/rho). Because of its simplicity, the
low-contrast approximation is subject to errors, particularly for
large positive contrasts in P-wave velocity associated with negative
contrasts in S-wave velocity. However, for incidence angles up to
40 deg and models confined to Deltabeta/beta < 0.25, the errors in
both coefficients are relatively small. Converted-wave AVO crossplotting
of the coefficients of the low-contrast approximation is a useful
interpretation technique. The background trend in this case has a
negative slope and an intercept proportional to the alpha/beta ratio
and the fractional change in S-wave velocity. For constant alpha/beta
ratio, an attribute trace formed by the weighted sum of the coefficients
of the low-contrast approximation provides useful estimates of the
fractional change in S-wave velocity and density. Using synthetic
examples, we investigate the sensitivity of these parameters to random
noise. Integrated P-wave and converted-wave analysis may improve
estimation of rock properties by combining extracted attributes to
yield fractional contrasts in P-wave and S-wave velocities and density.
Together, these parameters may provide improved direct hydrocarbon
indication and can potentially be used to identify anomalies caused
by low gas saturations.},
added-at = {2012-09-01T13:08:21.000+0200},
author = {Ramos, Antonio C. B. and Castagna, John P.},
biburl = {https://www.bibsonomy.org/bibtex/2d91391d899dfdedeed72bfb7a1148401/nilsma},
day = 1,
doi = {10.1190/1.1487114},
interhash = {2db8e81eee8dcd55001ad5dff1bfcd15},
intrahash = {d91391d899dfdedeed72bfb7a1148401},
journal = {Geophysics},
keywords = {geophysics seismics},
month = nov,
number = 6,
pages = {1721--1734},
publisher = {SEG},
timestamp = {2021-02-09T13:20:53.000+0100},
title = {Useful approximations for converted-wave AVO},
url = {http://dx.doi.org/10.1190/1.1487114},
volume = 66,
year = 2001
}