Geoscience Reference
In-Depth Information
The interpreter spends a large part of his or her working day looking closely at data on a screen
display. High-quality display screens are therefore important. As with any work involving sustained use
of a screen, mouse and keyboard, the physical design and siting of the units needs careful consideration
to avoid possible damage to health.
A1.2
Software
Decisions on which software should be made available on the system depend on consideration of
functionality and cost, and need to be assessed in detail for each individual installation. The main
problem from the point of view of the system administrator is usually the need to provide data transfer
between applications from different vendors. This can of course be reduced by restricting software
purchases to a single vendor, but even then there is likely to be a need to interface with proprietary
applications and databases. Where applications from several vendors are in use, system upgrades
(e.g. major updates to operating systems) can be very arduous, requiring updates to both software and
databases. Particularly when there is doubt about the reliability of hardware or software in the new
environment, it may be necessary to run both old and new environments in parallel, with a phased
transfer from one to the other; this needs careful liaison with interpreters and other users of seismic
data to avoid service interruptions at moments that are critically important to the business.
A1.3
Data management
Management of seismic trace data is for the most part not difficult, except for the huge volumes
involved. The data are organised in a very regular fashion, as values of amplitude (or other attribute)
on a regular 3-D grid. When data are retrieved, it is almost always along a plane or line or sub-cube
of the 3-D grid (e.g. as sections or traces). There is no requirement to identify individual samples
that satisfy complex selection criteria. This means that the data do not have to be held in a complex
database structure. Once the data have been loaded, usually from SEGY tapes, the files require little
further maintenance. Data loading is usually fairly easy for 3-D seismic traces. The main problem is the
specification of the spatial location of the traces, which is often done by manually typing in real-world
co-ordinates of particular points, e.g. of three corner points of the rectangular survey grid. This process
is potentially error-prone; small mistakes are difficult to spot once the data have been loaded but could
have disastrous consequences for accurate well positioning. Furthermore, there is scope for confusion
between different co-ordinate systems (projection, spheroid and datum). Sometimes position data are
supplied on one projection system and need to be transformed to another, to match against corporate
standards or to merge with another dataset. It is useful to have the services of a topographic surveyor
to ensure that the co-ordinate data as loaded are correct and in the desired projection system.
Loading seismic traces for a set of 2-D lines is much more difficult. The main problem is to work
out the relationship between trace number on tape and position data on a map; this can be quite simple
where the traces and positions are numbered sequentially along a line, but where a line has been
shot in several parts with discontinuities in numbering of traces and surface locations, it can be very
time-consuming to work out the relationships unless there is excellent paper documentation.
Management of seismic interpretation data (i.e. picked horizons and faults) is less simple. Because it
is easy to create new horizons, an interpreter at the end of a mapping project may have defined hundreds
of them. Most of them will be trial efforts to investigate different features of the data, perhaps over
very limited areas; usually a few dozen horizons will contain all the significant information. Cleaning
 
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