Page 323 - Acquisition and Processing of Marine Seismic Data

314 6. DECONVOLUTION

FIG. 6.1 Effect of the bandwidth on the resolution of seismic data. (A) Wide band (4–140 Hz), and (B) narrow band (4–60 Hz)
seismic data.

because a wide spectral band always corre- Deconvolution broadens the band-limited spec-
sponds to a better temporal resolution. As an trum,andeventriestoconvertitintoawhitespec-
example, Fig. 6.1 compares small portions of trum consisting of a balanced amplitude
wide (4–140 Hz, Fig. 6.1A) and narrow band distribution for the whole available frequency
(4–60 Hz, Fig. 6.1B) seismic sections, where the band. The theoretical basis underlying the use of
resolution is much better in the case of wide deconvolution to achieve these goals is basically
bandwidth. That is, the dominant frequency of to remove (at least, to compress) the source wave-
broadband data is relatively higher, which ulti- let embedded in the seismic data. The time length
mately results in a smaller wavelength, increas- of the wavelet before deconvolution is much
ing the resolution of the seismic signal. largerthanthatofthewavelet afterdeconvolution
Deconvolution has a number of significant (Fig. 6.2).
effects on seismic data, as shown schematically Although deconvolution is generally applied
in Fig. 6.2. In ideal conditions, the deconvolution to preprocessed shot or common depth point
(CDP) gathers, it can also be applied to stack sec-
• improves temporal (vertical) resolution
tions, which is known as deconvolution after
• removes or compresses the seismic wavelet
stack (DAS). If applied to prestack data, the
from the data
shots or CDPs must be properly preconditioned
• removes the ringy character of the reflections
and the coherent and random noise components
• eliminates multiple reflections
must be removed as far as possible, since the
• whitens the amplitude spectrum to obtain
quality of deconvolution output is quite sensi-
broad-band data
tive to noise in the data. Figs. 6.3 and 6.4
The recorded seismic data is band limited at compare the preprocessed shots and stack sec-
both high- and low-frequency ends of the spec- tions before and after a spiking deconvolution,
trum because of the ghost reflection notches and respectively. The deconvolution is especially
the high swell noise amplitudes, respectively. effective on the early arrivals and removes the