6. Drilling geophysics

As with logging, borehole geophysical techniques are implemented from a borehole.

• The objective is very different: drilling geophysical techniques aim to increase the radius of investigation of boreholes, to obtain information about the subsoil at greater depths than with surface methods, and with better resolution. It's an exploration of the ground in volume, rather than in points as with logging, where resolution is finer.

• Some methods use a single borehole.

  This is the case with the reflection-mode geological drilling radar, or the electric cylinder (registered by EDG – Européenne de Géophysique). The distance between the current electrode and the potential electrode is greater than the diameter of the hole (up to the length of the borehole), so that the...