|
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.