Flexural waves generated by a dipole source have been studied theoretically and used toestimate the shear parameters of a formation. The basic principles and main propertiesof flexural waves propagating in a borehole are reviewed in this paper. A mono/dipoletransducer made of a PZT piezoelectric tube is used for laboratory experiments inborehole models. The radiation pattern of the dipole source is measured in a watertank. In order to simulate the hard and soft formations, measurements are performedin borehole models made of aluminum and lucite, respectively. Experimental resultsare in good agreement with the theoretical dispersion characteristics. Measurementsare also performed with the transducers in an azimuthally anisotropic borehole modelmade of Phenolite XX-324. Both fast and slow flexural waves with different velocities aregenerated by a dipole source in the model. The flexural waves are related to the fast orslow shear waves in the anisotropic material. Experimental results show that the flexuralwave 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 aformation's anisotropy.
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