Abstract. As a method of exciting shear waves in acoustic logging, the phenomenon of SH wave propagation along cylindrical double-layered elastic media surrounding a fluid-filled borehole, excited by an annular shear stress source applied to the borehole wall, is studied. The dispersion equation and excitation characteristics of guided waves and critical refracted head waves described by vertical branch cut integrals are theoretically and numerically analysed. It is found that the dispersion behaviour of guided waves as borehole radius tends to infinity is the same as that of Love waves in a half-space model with horizontally double-layered elastic media, and that the lowest-order guided waves have non-zero low cut-off frequencies. The transient full waveforms of the SH wavefield are calculated and compared with the sum of the waveforms of the component waves. Both are in good agreement.

Keywords: SH wavefield, borehole, Love wave, guided wave, waveform

Print publication: Issue 2 (June 2005)
Received 21 January 2005, accepted for publication 19 April 2005
Published 20 May 2005