Page 424 - Acquisition and Processing of Marine Seismic Data

8.4 QC IN SORT AND BINNING 415

FIG. 8.10 Fold distribution for (A) no flex binning (static bin) and (B) flexed bin for 50% at near offsets and 150% at far
offsets. Bin size is 6.25 m 37.5 m for inline and crossline directions, respectively. After Mutter, J.C., Carbotte, S.M., Canales,
J.P., Nedimovic, M., 2008. A 3D MCS investigation of the magmatic-hydrothermal system at the East Pacific Rise 9° 50’N,
MGL0812 Cruise Report. http://www.marine-geo.org/link/data/field/Langseth/MGL0812/docs/MGL0812SciCruiseReport-102008.pdf.

8.4 QC IN SORT AND BINNING since the fold number may dramatically
decrease in these areas. Fig. 8.12 shows the effect
Quality control (QC) in the CDP sort and bin- of missed shots on the fold of 2D seismic data.
ning process is done by checking the database Fig. 8.12A illustrates the shot points between
parameters and CDP data. In the database, the shots 665 and 690 with several successive missed
most important parameter to check is the fold shots along a distance of 203 m, which has arisen
distribution along the line for 2D and the bin- from a time break signal issue in the gun control-
ning map over the whole bin grid for 3D ler during the acquisition; there were no shots
(Fig. 8.6). CDPs can be displayed and the num- between shot points 676 and 677 for a distance
ber of traces in the ensembles is controlled to of 203 m. The lack of seismic data in this zone
ensure that the trace numbers within the CDPs resulted in a data gap in the final stack section
decrease at both ends of the line. In the example after NMO stretch mute due to the lack of far off-
illustration in Fig. 8.11, the first and last 100 sets around CDP 2400 (Fig. 8.12B) where the
CDPs of a 2D seismic line are displayed with optimum fold decreases from 24 to 6
the fold distribution graph along the line. The (Fig. 8.12C and D). In seismic operations,
number of traces in the CDPs slightly increases decreasing the fold number under a certain
at the beginning of the line from 1 to the opti- threshold requires filling in the data gaps by
mum fold value of 48. However, the opposite sit- reshooting the areas of successive missed shots.
uation occurs at the end of the line: the fold After application of flex binning to 3D data,
decreases slightly from the optimum value of some QC tests are needed to ensure that the bin-
48 to 1. ning is performed properly. The objective of flex
Trace kill or missed shots result in variations binning is to obtain a fold distribution as uni-
in the optimum fold value. Especially the areas form as possible. After flexing, a more regular
of missed shots must be carefully examined, distribution of the fold value indicates that the