The full acoustic wavetrain in a laboratory model os a borehole

Abstract

We have studied the characteristics of acoustic wave propagation in a fluid-filled borehole, using as a laboratory model a cement cylinder 2 ft in height and 2 ft in diameter with a 14 in. borehole at the center. We recorded a full wavetrain consisting of a refracted compressional (P) wave, a refracted shear (S) wave, a number of modal waves, and a Stoneley wave. Exploiting the dispersive properties of the modal waves and the source-receiver frequency characteristics, we were able to isolate the S wave, which has important applications in petroleum exploration, but which has not been widely used since it is difficult to extract from the full wavetrain in sonic logging. The observed Stoneley wave had a very high amplitude at low frequency and showed little dispersion. The Stoneley wave velocity is closely related to the S-wave velocity, and can be used as an indirect means to obtain the S-wave velocity. In general, the arrival time of each component wave agreed with theory, but the amplitudes of the component waves did not.