Casing Collar Locator (CCL)
Casing collar locator tools (CCL) are among the simplest and most essential in cased hole electric line. CCL’s are typically used for depth correlation and can be an indicator of line overspeed when logging in heavy fluids.
A CCL operates on Faraday’s Law of Induction. Two magnets are separated by a coil of copper wire. As the CCL passes by a casing joint, or collar, the difference in metal thickness across the two magnets induces a current spike in the coil. This current spike is sent uphole and logged as what’s called a collar kick on the cased hole log.
By counting how many collars the CCL have passed, we can calculate the exact depth of the tool.