Amplitude Vs. Offset Analysis in Finely Layered Media
Herbert W. Swan
In 1987, it was shown that amplitude vs. offset analysis (AVO) can be
sensitive to small residual velocity errors. However, even when the velocity is
perfectly determined, serious AVO distortions remain due to normal
moveout
stretch, thin-bed tuning, differential tuning as a function of offset, and event
time misestimation. This presentation shows that all of these effects are
closely related, and can be analyzed in a unified framework. If the analytic
form of the observed AVO slope distortion is expanded in a Taylor series, the
first term represents the residual velocity error term found by Spratt, and the
second term represents the remaining distortion effects mentioned. In practice,
either term can be larger than the underlying lithologic AVO slope term being
estimated. For example, errors caused by wavelet stretch lead to a peak slope
distortion which is 61% of the peak zero-offset reflectivity, even though the
velocity field is uniform and the data are
moveout
corrected with the perfect
velocity. These errors become particularly troublesome in a finely layered
target zone, and must be considered during the processing and i terpretation of
AVO data.
AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.