An acoustic log. A well-logging record of the travel time (interval transit time) of the compression wave over a unit distance: and hence, a record of the reciprocal of the compressional wave velocity. The time for acoustic energy to travel a distance through the formation equal to the distance spanned by two receivers is the desired measurement. The units of such measurement are usually expressed in microseconds per foot. The interval transit time can be integrated to give the total travel time over the logged interval. For the borehole compensated sonic log, two transmitters (one above the receivers and one below) are pulsed alternately to produce an improved log; averaging the measurements tends to cancel errors due to sonde tilt or changes in hole size.
The sonic log is used in combination with other logs (e.g., density and neutron) for porosity, shaliness, and lithology interpretation. Integrated transit time is helpful in interpreting seismic records. See acoustic log.
