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We implemented an AVO inversion algorithm in V(x,z) media.
Our approach is a two-step inversion scheme:
- 2.5-D Kirchhoff inversion;
- AVO coefficient estimation.
Since the velocity model used in AVO analysis is relatively smooth, the
finite-difference forward modeling result is accurate enough in Kirchhoff
inversion. Both the synthetic and field data example can verify the accuracy
of the finite-difference scheme.
On the basis of (), we proposed another
pair of Kirchhoff inversion operators that have a more obvious physical
meaning. One is the specular reflection coefficient R, and the
other is R multiplied by the cosine of half of the specular incident angle,
. The reflection coefficient R, organized into
common-image gathers, is not only necessary in estimating the AVO intercept
A and slope B, but also essential to update the velocity model.
Through checking common-image gathers, we can update the velocity model and
produce a more accurate image. This feature will also prevent the velocity
error from propagating into the final AVO coefficients.
One of the fundamental differences between Kirchhoff inversion and Kirchhoff
depth migration is that Kirchhoff inversion has an extra weighting function
varying along the integral curves. We investigated the relationship between
the weighting function and double-square-root (DSR) equation in the
homogeneous medium. It is interesting to see that the weighting function
has double peaks in the common-offset configuration. This observation
tells us that the largest contribution to the image is not from the middle
of the integral curve, but from the two flanks. Therefore, it is very
important to include the locations of the two peaks in order to recover a
true-amplitude image.
We applied our algorithm to both synthetic and field datasets.
The synthetic example shows that this new scheme is very accurate in
calculating the reflection coefficient and the specular incident angle.
When applying our approach to the Mobil AVO dataset, we updated the velocity
model according to the common-image gathers.
Furthermore, we estimated the AVO coefficients, intercept A and
slope B, and then created a fluid-line expression of Vp/Vs anomaly.
Our result shows that there is a strong Vp/Vs anomaly in the middle
section that suggests a potential hydrocarbon indicator.
Next: Berryman: REFERENCESRocks as poroelastic
Up: Rickett, et al.: STANFORD
Previous: THE MOBIL AVO DATA
Stanford Exploration Project
7/5/1998