Salt-flank reflections

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Seismic Data Analysis
Series Investigations in Geophysics
Author Öz Yilmaz
ISBN ISBN 978-1-56080-094-1
Store SEG Online Store

Consider the stacked section in Figure 5.0-1a. While picking velocities in favor of the flat reflections, the steep flank of the diffraction hyperbola off the tip of the salt dome and the steeply dipping reflection off the flank of the salt dome are not stacked with sufficient strength. This inadequate definition of the diffraction and the steeply dipping reflection then causes migration after stack to respond somewhat poorly (Figure 5.0-1b). The stack with dip-moveout correction preserves the diffraction and the steeply dipping reflection as well as the flat reflections (Figure 5.0-1c). As a result, migration yields an image of the salt diapir that stands out clearly in contrast with the surrounding strata (Figure 5.0-1d).

Figure 5.0-1  Conflicting dips associated with salt flanks: (a) CMP stack without dip-moveout correction; (b) time migration of the stack in (a); (c) the stack with dip-moveout correction; (d) time migration of the stack in (c).

It is important to evaluate the two migrated sections (Figures 5.0-1b and d) from the viewpoint of an interpreter. Surely, by using the termination points of the nearly flat events in Figure 5.0-1b, one can trace the salt boundary without the need for proper stacking and imaging the reflection off the flank. However, by preserving this reflection on the stacked section and migrating it properly (Figure 5.0-1d), we attain a clue to migration velocity errors. Specifically, if the steeply dipping event that defines the salt boundary and the surrounding flat events cross over each other, we know that overmigration has occurred, and as a result, the salt diapir has not been delineated accurately.

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Salt-flank reflections
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