far trace time is:
on the geometry shown below, interval velocity between
any two points in the section is:
The apparent velocity, or stacking velocity (Vstk), is the velocity which yields the exact NMO from the NMO equation. Therefore, it could be derived from real seismic data with a T^2 - X^2 plot, an NMO analysis, or a computer velocity analysis (CVA). It is the only velocity which will yield the best stacked seismic section.
average velocity from a log analysis will yield very poor stacking
results unless the interval velocities are quite constant and
there is no dip on the reflections. The RMS velocity from log
analysis will yield adequate results, as long as dip is not extreme.
In horizontal bedding, we usually assume that Vstk from seismic
equals Vrms from log analysis. Thus NMO could be predicted from
well log data by using the appropriate arithmetic. Conversely,
stacking velocity can be transformed into interval velocity, which
will lead to correct time to depth conversion.
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