Page 368 - Acquisition and Processing of Marine Seismic Data

6.10 QC IN DECONVOLUTION 359

FIG. 6.44 An example marine shot gather (A) before, and (B) after surface consistent deconvolution. Decomposition is done
only for shot location.

can be done by use of the following analysis attenuation effects. In addition, random and
before and after deconvolution: coherent noise must be checked to ensure that
the noise amplitudes are not revived by decon-
i. Displaying the selected shot gathers
volution. Late arrivals of the shot and brute
ii. Preparing the common offset/brute stack
stacks are particularly important in terms of
sections
boosted noise amplitudes, since the reflection
iii. Analyzing the amplitude spectra of the
amplitudes at the deeper parts of the data are
selected shots
relatively low and the noise amplitudes may
iv. Analyzing the autocorrelograms of the
easily become dominant to genuine reflections
selected shots
at late arrivals. Phase and polarity of the output
Selected shot gathers (Fig. 6.47) as well as data may also be checked on the seabed reflec-
brute stacks (Fig. 6.48) or common offset sections tion to see if the correct phase information is pre-
(Fig. 6.49) before and after deconvolution appli- served after the deconvolution. If a zero phase
cation must be visually compared to analyze if conversion is aimed for, then the effectiveness
the resolution is improved after deconvolution. of the phase conversion can be analyzed by com-
The ringy character of the reflections must be paring the seabed reflections of input and
removed and the primary reflections should be output data.
clearer after deconvolution, especially at the In order to obtain the optimum Wiener
deeper parts of the data where the seismic reso- deconvolution output, several tests may be
lution is relatively low due to the severe needed to select the operator length and