Near Surface Geophysics > Acoustic logging and cementing

Acoustic logging is run, mainly to measure the velocities of the geological formations. In full wave form acoustic logging, monopole-type tools are the most commonly used. Sources and receivers are multidirectional.

In vertical wells, the monopole tools are used to record five propagation modes:

  • The refracted compression wave,
  • The refracted shear wave - only in fast formations,
  • The fluid wave,
  • Two dispersive guided modes: the pseudo Rayleigh waves (only in fast formations) and the Stoneley waves.

If the acoustic tool is run in a cased hole poorly cemented, we can observed some resonances due to the poor coupling of the casing to the formation introduced by a poor cementing. It is the case of the borehole drilled on the Vesdun experimental site.

The example shows the effects of a poor cementing on the acoustic data. In the example, you have used the procedure based on Singular Value Decomposition, described in the Poitiers integrated field case, to compute the acoustic logs.