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Optimization Of Subsalt ImagingNormal access

Authors: Uwe Albertin, S. Kapoor, Wenfong Chang, Nigel Purnell and Tom Leary
Event name: 6th International Congress of the Brazilian Geophysical Society
Session: Deep Water, Subsalt and Overthrust
Publication date: 15 August 1999
Organisations: SBGf
Language: English
Info: Extended abstract, PDF ( 419.36Kb )

Successful subsalt imaging in the Gulf of Mexico depends critically on three aspects of the imaging
process; the building of an accurate sediment velocity model, defining the geometry of the salt body or
bodies, and successful application of 3D poststack and prestack depth migration algorithms. Even if the
target subsalt dips are moderate, steep dip imaging is often necessary for defining the geometry of the
salt bodies, parts of which may have significant dip. In addition, even though energy that propagates
through salt may be dip-limited because of the sharp velocity contrast between sediment and salt, energy
that propagates laterally from outside salt may also contribute to the flanks of subsalt reflectors with
steep dip. In such areas careful processing to preserve dips is necessary, with the ultimate goal being a
subsalt image that is as interpretable subsalt as it is outboard of salt. Here we discuss several
techniques for optimizing steep-dip salt and subsalt imaging, including iterative prestack depth migration
and velocity updating for sediment velocities, iterative prestack and poststack depth migrations for salt
boundary definition, proper interpretation of the salt boundary, and optimal application of a Kirchhoff
algorithm for final imaging. These techniques are illustrated with examples from an area of significant
complexity in the Gulf of Mexico.

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