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

of seismically derived velocities. Vinton Dome has a long production history resulting in
an abundance of well control. Well data are often used to update a velocity model by
providing information regarding well ties because they provide values for vertical
velocities and as such are suitable for depth conversion (Schultz, 1999) but are regarded
by some as inappropriate for a velocity model. Issues of velocity differences between
well logs and seismic velocities typically preclude their exclusive use to build an initial
velocity model. In this survey I used eighteen sonic logs to build an initial sediment
velocity model. None of the wells were deviated and any borehole drift that may have
occurred was not great enough to be detected with the lower resolution seismic data.
Positioning of most of these wells was close to the flanks of the dome where the majority
of production is located.
I plotted wells to determine their spatial relationship to each other and to the salt.
Smoothing the log curves reduced the spurious effects of outliers caused by well bore
conditions such as washout. I generated a 1-D, V z , velocity gradient from the sonic logs
biasing the farthest log from the salt to derive the gradient. I weighted this log because I
regarded the velocities from it as reflecting the regional velocity trend (Figure 48).
I picked seven geologic horizons on PSTM data. To fill gaps created by the throw of
faults and to bridge the gap created by the salt I interpolated and smoothed the horizons.
Smoothing the horizons in this manner allowed me to create a reference that had a basis
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