| Summary: | Flexural waves generated by a dipole source have been studied theoretically and used to
estimate the shear parameters of a formation. The basic principles and main properties
of flexural waves propagating in a borehole are reviewed in this paper. A mono/dipole
transducer made of a PZT piezoelectric tube is used for laboratory experiments in
borehole models. The radiation pattern of the dipole source is measured in a water
tank. In order to simulate the hard and soft formations, measurements are performed
in borehole models made of aluminum and lucite, respectively. Experimental results
are in good agreement with the theoretical dispersion characteristics. Measurements
are also performed with the transducers in an azimuthally anisotropic borehole model
made of Phenolite XX-324. Both fast and slow flexural waves with different velocities are
generated by a dipole source in the model. The flexural waves are related to the fast or
slow shear waves in the anisotropic material. Experimental results show that the flexural
wave splits into a fast and a slow component in an azimuthally anisotropic borehole;
therefore, dipole acoustic well logging could be an effective means for estimating a
formation's anisotropy.
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