3-D seismic data acquisition and processing - 3-D Seismic Interpretation - page 35

surveys. Jack ( 1997 ) gives an excellent introduction to the subject, which is considered
in more detail in chapter 8 .

2.5 3-D data processing

As with the section on data acquisition, we do not aim to give here a complete overview
of seismic data processing. Rather, we will again concentrate on the differences between
2-D and 3-D. Yilmaz (1987) gives a detailed but very readable account covering all
aspects of data processing.
In most respects 3-D data processing is very similar to 2-D data processing. Indeed,
any process that treats traces individually, such as statistical deconvolution, gain recov-
ery, trace muting and frequency filtering, is applied in an identical manner in 3-D and
in 2-D. Some of the other processes are applied in a 2-D sense, along lines rather than
across the 3-D data volume.
There are three main processes that are different for 3-D data: binning, spatial fil-
tering, and any process that repositions data such as migration and dip moveout. In
addition several other applications, although generally run on selected lines from the
3-D volume, may benefit from the prior application of one of the above. An exam-
ple of such a process is velocity analysis, which is normally run on a regular grid
of 2-D lines but will improve in quality after 3-D migration. An important aspect of
3-D data processing is to ensure spatial consistency of parameters such as the velocity
field.
Figure 2.21 shows a typical processing sequence for 3-D data. We will briefly run
through all the steps, but those that are significantly different from 2-D processing are
highlighted in bold and will be discussed in more detail.
Modern commercial processing systems contain hundreds of algorithms. There are
often several ways to tackle any given problem and the processing analyst may have to
try several different techniques and parameters before being satisfied that any particular
step is optimised. It is not possible in this topic to even introduce all of the techniques
but the reader is referred to Yilmaz (1987) and Hatton et al. ( 1986 ) for more detailed
descriptions.

2.5.1 Reformat, designature, resampling and gain adjustment

The first step in fig. 2.21 is a reformatting operation. This just takes the data coming
from the receivers and puts them into trace order. Normally the data are written to
tape at this stage in one of the designated industry formats so that the raw records are
retained to form the basis of possible later reprocessing. If starting from field tapes,
reformatting includes converting the data from standard industry format into whatever
format the processing system uses. The second step, designature, takes the wavelet