Page 390 - Acquisition and Processing of Marine Seismic Data

7.2 PREDICTIVE DECONVOLUTION 381

FIG. 7.16 (A) A high-resolution shallow seismic line with a first-order multiple (M 1 ), and (B) output of the predictive
deconvolution for n ¼ 160 ms with a water depth-dependent prediction lag. Autocorrelograms of the sections are given in
the bottom panels.

prediction lag of α ¼ 40 ms. The most suitable multiples and primaries interfere, become much
operator length for the shot in Fig. 7.15 is more distinct.
n ¼ 80 ms, which removes almost all of the mul- The theoretical foundation of predictive
tiple energy from autocorrelograms of the deconvolution is based on the periodicity of
deconvolution output. the multiples in shot gathers or CDPs. The peri-
Fig. 7.16A shows a shallow seismic line along odicity, however, is only completely preserved
which the water depth slightly changes. Uplift- in zero-offset sections, and therefore predictive
ing of the acoustic basement results in a trans- deconvolution may not be perfectly successful
parent and reflection-free zone at the center, in on nonzero offset data, such as shot or CDP
which the first-order multiple (M 1 ) is clearly vis- gathers. In some cases, predictive deconvolution
ible. Autocorrelograms of the input section indi- is applied to the stack sections. On the other
cate that the period of the multiple also changes hand, a suitable result may not be achieved since
as the water depth increases. Therefore, a pre- the stacking modifies the amplitude relations
diction lag varying from 240 to 340 ms depend- between the primaries and the multiples. In fact,
ing on the water depth is used with an operator the only domain where the periodicity and
length of 160 ms. The output of predictive amplitude relationships are preserved is the
deconvolution shows that most of the first-order slant stack (τ-p) domain, and the multiples can
multiple energy is suppressed (Fig. 7.16B), and be better suppressed by predictive deconvolu-
the primary reflections of the deeper parts of tion applied in the slant stack domain. In the fol-
the righthand side of the section, where the lowing section, the theory and practice of the