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

etween two closely spaced well bores. The well-based model on two perpendicular
traverses imaged the faults more sharply than did the prestack time migrated velocity
model PSDM. Differences in the depth of events indicate that the well-based model is
faster. The question is which is correct or has the higher fidelity. On the prestack time
migrated velocity model PSDM, the Anahuac horizon pick leads into what is likely salt,
and was interpreted as such on the PSTM. Another example of improved fidelity is in the
higher resolution of the well-based PSDM in the depth slice. Comparing depth slices
both faults and the salt have greater fidelity in the well-based PSDM based on the events
being better focused resulting in coherent events in the well-based volume. Generating
synthetic seismic was another method of tying the wells to the seismic. In these
examples the closest match of the synthetic was to the well-based velocity modeled
PSDM seismic.
Differences in the quality of the migrated volumes can be due to several reasons.
Generating velocities from time migrated common mid-point (CMP) gathers with
velocities that were not as accurate is one way to explain the differences in quality. This
is a reasonable explanation why the bright spot did not exist. Reduced accuracy of
velocities can result from problems that are inherent with 3-D land surveys such as poor
receiver coupling, background noise from cultural sources such as traffic and power lines,
and a variety of other known sources of noise. Affecting data quality may be differences
in the modeling. Transforming velocities from RMS to time interval velocities and then
to depth interval velocities is necessary with a prestack time migrated velocity model.
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