SPWLA Glossary

A well log of the interval transit time: i.e., the time required for a compression wave to travel one foot in the formation (generally in microseconds per foot); the reciprocal of the compressional velocity. The borehole compensated sonic sonde carries two sets of transducers, one with its transmitter above its receiver pair and one with its transmitter below. The transmitters are pulsed alternately, and the alternate measurements are averaged. Spurious effects caused by borehole-size changes, and sonde tilt, which would affect a measurement with a single set of transducers, are thereby substantially reduced.