Energy Partitioning and Attenuation of Guided Waves in a Radially Layered Borehole
Name
1985.3 Burns et al.pdf
Size
578.85 KB
Format
Adobe PDF
Checksum (MD5)
81088f2f0b1618c06c6164541ff6862b
Author(s)
Burns, D. R.
Cheng, C. H.
Toksoz, M. N.
Date Issued
1985
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1985-03
Abstract
Recently published results (Tubman et al., 1984; Baker,. 1984) indicate that
synthetic full waveform acoustic logs generated in cased or damaged boreholes
differ significantly from those generated in an open hole with the same formation
parameters. In particular, the guided waves appear to be the most affected by such
radial layering. In order to gain some understanding of these effects, the amplitude
response and energy distribution of the pseudo-Rayleigh and Stoneley waves are
studied for the cased and invaded borehole models. The expressions derived by
Cheng et al. (1 982) are used to calculate partition coefficients (partial derivatives
of phase velocity with respect to body wave velocities) for the guided wave modes.
The attenuation of the guided wave can then be represented by the sum of the layer
attenuation values weighted by their respective partition coefficients. The results
indicate that the attenuation of the Stoneley wave is dominated by the fluid
attenuation at all frequencies in fast formations, both in the open hole geometry and
in the presence of casing or invaded zones. In a slow formation, the Stoneley wave
attenuation becomes more sensitive to the shear wave attenuation of the formation
at higher frequencies in both the open and cased hole situations. For the pseudo-Rayleigh
wave, the introduction of casing reduces the effect of the fluid attenuation,
while the presence of an invaded zone reduces the effect of the formation shear
attenuation. Plots of the partition coefficients indicate that the casing and invasion
layers are most important over a limited frequency range which is related to the
thickness of the layer. Radial displacement curves illustrate the depth of penetration
of the various frequency components of the pseudo-Rayleigh wave.
Persistent DSpace Link
