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TAU Migration and 
Velocity
Analysis: Application to Data from Midyan Region
of the Red Sea
By
Tariq A Alkhalifah1
(1) KACST, Riyadh, Saudi Arabia
Imaging the pre-salt reflections for data acquired from the coastal region
of the Red Sea is a task that requires prestack migration velocity analysis.
Conventional poststack time processing methods lacks the lateral-inhomogeneity
capability needed for such a problem. Prestack migration velocity analysis in
the vertical time domain reduces the velocity-depth ambiguity usually hampering
the performance of prestack depth-migration velocity analysis. In prestack TAU
migration velocity analysis, we keep the interval velocity model and the output
images in time. This allows us to avoid placing reflectors at erroneous depths
during the velocity analysis process, and, thus, avoid inaccurately altering the
shape of the velocity model, which, in turn, slows down its convergence to the
true model. Using a one-dimensional velocity update scheme, the prestack TAU
migration velocity analysis produces good images of data from the Midyan region
of the Red Sea. For the first seismic line from this region, only three prestack
TAU migration velocity analysis iterations were required to focus pre-salt
reflections in time. However, the other line, which crosses the first line, is
slightly more complicated, and thus, required five iterations to approach the
final, reasonably focused, time image. These results compared favorably with
images obtained for the same two lines using the Common-focus-point imaging
technique, developed recently at Delft University. After mapping both images to
depth using the final velocity
models, the placement of reflectors in the two
2-D lines were consistent at their crossing point. Some errors occurred due to
the influence of out-of-plane reflections on 2-D imaging. However, such errors
are identifiable and are generally small.