| Summary: | In order to investigate the effect of borehole fluid viscosity on the attenuation and
dispersion of the guided waves present in full waveform acoustic logs, the problem of
wave propagation in a borehole containing a viscoelastic fluid surrounded by an infinite
elastic formation is solved using boundary layer theory. The results indicate that the
losses due to viscous drag along the borehole wall are a small component of the overall
guided wave attenuation for the frequencies of interest in full waveform acoustic logging
(2-15kHz) and for reasonable viscosity values (1-1000cP). These losses, however, can be
significant at low frequencies. In addition, the variations in viscosity have a negligible effect on the guided wave dispersion for this range of frequency and viscosity. These findings indicate that friction between grains in fluid suspension may be the dominant attenuation mechanism in the drilling fluids present in boreholes.
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