Wavelet Dispersion and Bright-Spot Detection
Peter C. Luh
Since Ostrander in 1984 showed that the variations in reflectivity as a
function of offset can be used for bright-spot validation, it has been known
that these variations are often sensitive to errors in acquisition and
processing of prestack seismic data. This presentation shows that even with
perfect measurements, the bright-spot signal will be altered because the wavelet
disperses as it propagates through an attenuating overburden. This in turn
affects the slope term of the amplitude vs. offset (AVO) variation. For any
single reflector, the dispersion of its propagated signal as a function of
offset can be decomposed into a product of the vertical and horizontal
dispersions. The vertical dispersion is the dispersion that a zero-offset
arrival suffers through its propag tion, and the horizontal dispersion is the
additional dispersion that a nonzero-offset arrival must suffer further because
of the residual normal moveout
time. Numerical examples using a
frequency-independent attenuation law show that even for a relatively high-Q or
low-loss overburden, the horizontal dispersion alone can distort the AVO signal.
This distortion cannot be taken care of by
velocity
analysis. A preferred method
to overcome the dispersion effect would be to apply Q compensation on prestack
seismic data before movement.
AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.