Sirgue, Laurent, 2003. Inversion de la forme d'onde dans le ...

Chapter 1
Introduction
Seismic exploration techniques are used to determine the geological structure of the subsurface
as a routine component in the search of hydrocarbon reservoirs. The seismic acquisition experiment
is triggered by a controlled source which in turns, initiates a propagating wave within
the earth that is ultimately recorded at the surface by receivers. The recorded signal is then
processed in order to determine a model representing the geological structure of the subsurface.
This model is most often characterised by the propagation velocities and is in practice, most
often decomposed by spatial scales: the low wavenumbers define the large scales of the model
while the high wavenumbers describe the fine details of the structure.
This decomposition by scale is an approach that is justified by the information content of
the experiment. Jannane et al. (1989) showed that typical near offset, seismic reflection data are
sensitive only to the very low and the very high wavenumbers; the intermediate wavenumbers
are invisible to the data. The standard approach in exploration imaging has, as a result, evolved
into a recovery of the low wavenumbers of the velocity field (macro-model) followed by the
reconstruction of the very high wavenumbers components. During the last decades, this decomposition
has been successfully applied to many areas of seismic exploration presenting simple
geological structure. More recently, seismic exploration targets have included geographical areas
in which the subsurface contains more complex features. Examples include areas with significant
salt flows (Ward et al., 1994), or significant amounts of volcanics (Planke et al., 1999),
both of which cause severe imaging problems. The strong heterogeneity as well as the 2D/3D
nature of the media significantly diminish the efficacy of standard imaging techniques. The
most widely used methods for imaging complex media are prestack depth migration. These approaches
however, are currently still applied within the standard approach, in which no attempt
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