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 Ratcliff et al. (1995). After applying prestack depth migration, the discontinuity of the reflector can be partially explained as an illumination problem Muerdter et al. (1996). 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 Wyatt et al. (1997), 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.