Editing Wireline (cabling) (section)

====Cement bond tools====
A [[cement bond tool]], or CBT, is an [[acoustics|acoustic]] tool used to measure the quality of the cement behind the [[casing (borehole)|casing]].  Using a CBT, the bond between the casing and cement as well as the bond between cement and formation can be determined.  Using CBT data, a company can troubleshoot problems with the cement sheath if necessary.  This tool must be centralized in the well to function properly.

Two of the largest problems found in cement by CBT's are channeling and micro-annulus.  A micro annulus is the formation of microscopic cracks in the cement sheath.  Channeling is where large, contiguous voids in the cement sheath form, typically caused by poor centralization of the casing.  Both of these situations can, if necessary, be fixed by remedial electric line work.

A CBT makes its measurements by rapidly pulsing out [[compressional wave]]s across the well bore and into the pipe, cement, and formation.  The compressional pulse originates in a [[transmitter]] at the top of the tool, which, when powered up on surface sounds like a rapid clicking sound.  The tool typically has two receivers, one three feet away from the receiver, and another at five feet from the transmitter.  These receivers record the arrival time of the compressional waves. The information from these receivers are logged as travel times for the three- and five-foot receivers and as a micro-[[seismogram]].

Recent advances in logging technologies have allowed the receivers to measure 360 degrees of cement integrity and can be represented on a log as a radial cement map and as 6-8 individual sector arrival times.