Borehole flexural modes in anisotropic formations

A perturbation method of solution is an efficient way of analyzing elastic wave propagation along a borehole in anisotropic formations. The perturbation model allows us to calculate changes in the modal dispersion curves caused by the differences in elastic constants between the anisotropic formation of interest and a reference, or unperturbed, isotropic formation. The equivalent isotropic constants in the reference formation are obtained from the appropriate compressional and shear-wave velocities for the selected propagation and polarization directions of the flexural model. The flexural wave excitation function is a measure of the energy that a source converts to flexural motion. An expression is deduced for the flexural wave excitation and show that its band limited characteristic is influenced by both the borehole diameter and formation parameters. -from Authors