34 Well seismic surveying and acoustic logging too much noise can make it difficult to identify the start of the wave, which is the case particularly with the signal in the most distant borehole. 1.2.3.2.1 Sources To maximize the energy of shear waves, it is recommended that a source that is mechanical (hammer-anvil) or electromechanical (similar to the sources of the PS Suspension Logging (PSSL) tool) should be anchored to the wall (Figure 1.20). Figure 1.20 Illustration of a mechanical (Ballard anvil hammer) and an electrodynamic (SolGeo, mass moved up or down by an electromagnet) S source. 1.2.3.2.2 Receivers For P-waves, energy is distributed over the horizontal components, which can generate difficulties in picking the first arrivals and requires a mathematical polarization operation to project the energy in the source-receiver direction. Some receivers can be oriented in a given direction. However, the most simple and robust method is to use hydrophones to measure the P arrivals. It should be noted that some hydrophones are directly equipped with an amplification system to optimize recording dynamics. For S-wave analysis, only a single 1-component receiver is needed. However, having a 3-component receiver associated with the mechanical source makes it possible, if required, to verify P measurements with the sparker-hydrophone combination (Figure 1.21).
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