Which log is used to sense fluctuations in borehole diameter?

The caliper log is specifically designed to measure the diameter of the borehole as it is being drilled. This log provides crucial information about the shape and size of the wellbore, allowing for the detection of fluctuations in diameter caused by factors such as borehole instabilities, formation collapse, or the presence of cavities. By using arms or mechanical probes that extend against the walls of the borehole, the caliper log can accurately record variations in the borehole's width at different depths, which is essential for evaluating the integrity of the borehole and ensuring proper well completion.

In contrast, the acoustic log measures the velocity of sound waves through the formation, which can give insights into rock properties but does not measure borehole diameter. The drilling log documents the progress and details of drilling operations but doesn’t measure physical characteristics of the borehole itself. The gamma log detects natural radioactivity within formations to provide information about lithology and can help in identifying various rock types, but it also does not provide direct measurements of borehole diameter. These distinctions clarify why the caliper log is the appropriate tool for sensing fluctuations in borehole diameter.