Abstract: The curves of the dispersion and sensitivity for the mode waves in the borehole surrounded by a transversely isotropic elastic solid are numerically simulated. The results show that the flexural wave is sensitive to the velocity of the vertically propagating shear wave (v_SV), while the Stoneley wave is sensitive to the velocity of the horizontally propagating shear wave (v_SH). In the slow formation, the investigating depth of the Stoneley wave is about 1.5 radius of the borehole to the wall for the full calculating frequency range; the flexural wave exhibits frequencydependent characteristic of the radial depth of investigation, and the investigating depth is deep (about 4 radius of the borehole) with low wavenumbers and shallow (about 1.5 radius of the borehole) with high wavenumbers. In the fast formation, the sensitivity of the flexural wave to the v_SV diminishes slightly, but the sensitivity of the Stoneley wave to the v_SH diminishes significantly due to the influence of the fluid filled in the borehole.

Key words: transversely isotropic elastic formation, flexural wave, Stoneley wave, investigating depth, sensitivity