Table T1. Overview of borehole acoustic modes.
Mode
Type
Features
Range of velocity
P and S head waves Partially reflected compressional and shear waves Governs compressional and shear head wave Vm = VP , Vm = VS
P and S normal modes Fully reflected compressional and shear waves Fully trapped, dispersive, dominate signal in far field Vm < VP , Vm < VS , velocity different from formation velocity
Stoneley wave Interface wave, fundamental mode Velocity and attenuation depend on formation permeability 0.75 VF < Vm < VF

Notes: Adapted from Hearst et al. (2001). VP = compressional acoustic velocity of the wave spreading in a medium, VS = shear velocity, VF = velocity of the waves in the borehole fluid, Vm = velocity of the particular mode.