We investigated the phase-velocity dispersion and excitation intensity features of the Stoneley,flexural,and screw waves,respectively,for acoustic logging-while-drilling (LWD) in vertical wells surrounded by transversely isotropic formations.The sensitivity coefficients of those modes with respect to all elastic parameters are evaluated.And the comparisons between the LWD and conventional wireline logging are present.It is revealed that the monopole Stoneley waves at low frequencies can be applied for the inversion of the horizontal shear modulus (c66)using the LWD data because that parameter governs the velocities of low-frequency Stoneley modes.The propagation velocities of flexural modes do not tend to the shear velocities in the whole frequency range in a slow formation.The flexural-wave velocities,however,have a nearlylinear relation with the shear velocities in higher frequencies (e.g.,at 6 kHz).Thus we can indirectly estimate the shear velocity using a dipole sonic logging tool even in a slow formation.Similar to the wireline logging,the screw modes excited by a quadrupole can also be used for the effective measurement of shear velocity.