Casing Inspection - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 236

For practical results, this tool requires an unweighted fl uid in the hole. With
muds above 10 lb/gal, the signal is so attenuated as to give a useless log. Figure 13.18
illustrates the physical tool construction and modus operandi.
There are also wellbore inspection devices that use TV cameras and an
intense light source to record and transmit visual images of the borehole wall to
the surface. Figure 13.19 gives some examples of such images. Borehole televi-
sion cameras provide digital records that can be viewed in real time when an
immediate diagnosis is required as to the cause of obstructions in, or damage to,
the casing.
Fig. 13.18 Ultra sonic
imager (USI). Courtesy
Schlumberger