The acoustic velocity anomalies have several origins:
The refracted acoustic wave can propagate in the washed or invaded zone of the formation due to the invasion phenomenon and not in the virgin zone. The seismic wave (VSP) emitted at the surface propagates mainly in the virgin formation. In order to obtain acoustic velocities in the uncontaminated zone, it is necessary to correct or calibrate the acoustic velocity log on measurements of the propagation time in a virgin zone provided by the VSP.
The acoustic logs are measured in depth. The velocity log can be used to obtain a time-depth law by integrating the acoustic transit time as a function of depth. The integrated transit time can be used to convert a log in depth into a log in time. The logs in time can be inserted on the seismic sections for calibration in time.
We describe: