Finally the majority of the logs are very sensitive to the variations of the borehole diameter. It is thus essential to run a caliper log who records variations of the borehole diameter. Moreover variations of diameter can give indications on the zones under compacted or on the contrary on the existence of swollen clay zones for example.

Picture of the caliper

Various types of calipers

Variation depending on shape of the boreholes.

Essential to obtain quantitative values of density and porosity, the measurement of the diameter of the borehole can be done with more or less sophisticated tools. The tools with several arms make it possible to evaluate the ovalization of the borehole.