A Deterministic Evaluation of eismic Fidelity using Velocity Modeling ...

ased data, indicating higher fidelity because seismic events are in their proper x, y, and z
space. A section perpendicular to the traverse in Figure 65 also images fault planes that
are more coherent in the well-based section. Another interesting observation is the event
that intersects the Anahuac well pick when followed eastward merges into an event that is
salt on the PSTM (Figure 65). Observing the depth sections of both velocity models also
provides differences in the data set for comparison (Figure 66). Imaging of faults and
the salt are more coherent in the depth slice from the well-based PSDM than from that of
the prestack time migrated velocity model PSDM.
Another illustration of the improved fidelity provided by the PSDM is from the drilling of
a bright spot interpreted with the PSTM (Figure 67) near the salt flank. A comparison of
the PSDM from both the well-based velocity model and the prestack time migrated
velocity model show that there is no bright spot. Analysis of the PSDM shows that there
is salt at that location, although the impedance contrast is not as great as it is shallower
(Figure 68). There are two issues in the differences of the PSTM and the PSDM that
further demonstrate the improvements in imaging provided by the well-based PSDM.
The first is the bright spot that appears in the PSTM but is not in the PSDM. An
explanation for this is that incorrect modeling of velocities close to the salt flank resulted
in constructive interference of noise. This explanation is appealing because of the close
proximity to the salt and the inherent difficulty of imaging salt flanks with PSTM. Both
of the PSDM seismic volumes do not image a bright spot demonstrating the ability of
PSDM to image in areas of strong lateral velocity changes. The second issue is the
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