SPWLA Glossary

An elastic wave, seismic wave. A sound wave in which the disturbance propagated through a medium is an elastic deformation of the medium. The wave train which results from the emission of an acoustic pulse by a well logging device is detected by one or more detectors mounted on the sonde and various aspects of it are measured (see acoustic log). The wave train is a composite of various modes of energy transfer. The first arrival usually results from compressional waves traveling in the formation; the inverse of its velocity is measured by sonic tools. A second arrival is sometimes identified as shear waves traveling in the formation. The velocity of the compressional waves traveling through the mud is frequency dependent and has relatively high frequency content. On the other hand, surface waves of relatively low frequency travel along the borehole wall at lower velocities and are usually called tube waves or pseudo-Stoneley waves. See also wave train.