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Hydrocarbons are often trapped under the edges of salt bodies making
accurate imaging essential. The complex velocity structure associated
with the surrounding subsurface and the salt itself can mask deeper
reflectors making structural and stratigraphic interpretation difficult if
not impossible. It is a well established fact that prestack depth migration
is the most accurate approach for imaging laterally varying media
(). After applying prestack depth migration, the discontinuity
of the reflector can be partially explained as an illumination problem
(). This illumination problem can lead to apparent residual
curvature in the common reflector point domain. This apparent residual
curvature and migration artifacts cause problems with stacking and velocity
estimation (), ultimately deteriorating the quality of the final
image.
A 3-D dataset from the North Sea provided by Elf clearly shows a deep reflector
that, after migration, becomes discontinuous under the edge of a salt body.
Analysis of a 2-D synthetic model based on this real dataset leads to the
conclusion that in this case the complex velocity structure results in poor
illumination of the reflector of interest. This lack of energy causes the
reflector to disappear and gives incorrect amplitude results.
In this paper we identify the problem areas on the real and
synthetic dataset. We then analyze the anomaly using finite-difference
generated data and pre-stack Kirchhoff depth migration. Raytracing
techniques allow us to investigate the problem of illumination. Finally,
we propose possible solutions for this case.
Next: Background
Up: Rickett, et al.: STANFORD
Previous: Prucha, et al.: Anti-aliasing
Stanford Exploration Project
7/5/1998