Introduction - 3-D Seismic Interpretation - page 13

1.5 Road map

Chapter 2 is devoted to explaining how 3-D seismic data are acquired and processed.
The interpreter needs to have at least an outline knowledge of these topics, for two
reasons. One of them is the need to understand what the limitations of the data are.
Often, the interpreter is struggling to get as much information as possible out of a
seismic dataset, and has to decide how far his conclusions are robust, or whether there
is a chance that he is being misled by noise. The other reason is that the interpreter will
be asked, when his best efforts still leave him unsure about the subsurface picture, what
can be done to improve the data. He will then sometimes find himself in a dialogue with
acquisition and processing experts, and need to speak their language. Chapter 2 aims at
equipping him to do this. Although most space is given to the specific issues that arise
for 3-D, the methods that are no different from the 2-D case have been sketched in to
give a reasonably complete account.
Chapters 3 and 4 describe the basic interpretation process. The distinction between
structural and geological interpretation is an artificial one, in the sense that both are
going on simultaneously as the interpreter works through his data. However, many
interpreters spend much of their time making structural maps or planning well trajecto-
ries. Therefore, the basic mechanics of workstation interpretation are covered at some
length in chapter 3 . Chapter 4 considers some of the ways that 3-D seismic can lead
to enhanced geological understanding, and what some of the problems are, especially
because of the limited resolution of seismic data.
The availability of dense grids of data has revolutionised our ability to make useful
inferences from measuring seismic attributes, such as the detailed study of amplitudes of
individual seismic loops. This topic is therefore covered in detail in chapter 5 . Inversion
of seismic data to acoustic impedance is covered in chapter 6 ; this is an old idea that
has become much more useful with the availability of high-quality dense 3-D datasets.
It converts the standard seismic section, which emphasises the layer boundaries where
reflections occur, into a form that emphasises the properties of individual layers. This
can then be a starting-point for discussions with other disciplines, for example the
reservoir engineer.
An area of rapid progress at present is the use of more powerful computer worksta-
tions to give the interpreter a better appreciation of the 3-D nature of the subsurface,
viewing 3-D bodies directly rather than just seeing 2-D sections through them. This is
explained in chapter 7 .
There is increasing interest in using repeated surveys over producing fields to follow
changes in seismic response produced by changes in porefill (e.g. development of a
gas cap); this is another old idea that has become more feasible with the availability of
high-quality 3-D surveys. Such surveys, usually called 'time-lapse' or '4-D' seismic,