Migration Velocity Analysis Using Seismic Diffractions

Speaker: Via Ramadlona

 

Abstract

Diffraction events containing information about small geologic features in the subsurface such as faults, channels, pinchouts, etc. Typically, the energy retained by diffraction events have one or two orders of magnitude weaker than the one retained by the reflections. These fact as a reason that diffraction analysis be a challenging problem. Correct identification and use of diffraction events is important also for velocity estimation and can be carried out in the prestack as well as in the post-stack domain. Using synthetic and real data examples, we present the influence of velocity on the appearance of the migrated diffractions and conclude with a few remarks on the possibility to separate diffractions from reflections after migration. In order to use diffractions for velocity analysis, a domain in which migrated diffractions will show high sensitivity to velocity variations used the dipangle common-image gathers. The post-migration dip-angle domain discovered significant distinction between diffractions and reflections. In this domain after migration with the correct velocity reflections appear as concave-shaped events while diffractions are flat. The separation can be used to eliminate the migrated reflections from the common-image gathers and will improve the identification and analyis of the relatively weak diffractions.

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