Casing Collar Locator (CCL)

Definition - What does Casing Collar Locator (CCL) mean?

Casing Collar Locator is an electrical logging tool used in cased holes to identify, correlate, and confirm the depths of casing collars or tubing in the well with some known reference points on the casing string. This is mainly used for correlation purpose or to identify the short collars. Casing Collar Locators are available in different sizes and specifications to deal with different casing, tubing sizes, temperatures and pressure conditions.

Petropedia explains Casing Collar Locator (CCL)

The CCL tool is employed in almost every cased well because it provides vital information about the exact depths of the casing collars, number of short collars etc., which is essential for depth correlation, packer setting, perforations, extent of casing damage and other downhole operations.

Principle: CCL tool comprises a magnetic device that senses the increase in metal mass at casing or tubing collars.

Tool design: The tool comprises of a downhole amplifier, coil and magnet arrangements. The arrangement of the system is in such a way that the two similar facing magnetic poles are placed on either side of the coil and other arrangements are on either side of the magnet two coils as shown in the figure below. Coils are provided with thousands of turns to achieve strong currents which are enough to be identified at the surface. When, the tool passes through the collar joint it experiences increase in metallic mass. This causes a change in magnetic field around the coil inducing low frequency voltage. This signal is amplified and read out at surface in the form of spike known as collar kick or disturbance.

CCL is mostly run with wireline logging mode (conducting line) and sometimes run on slickline (Non-conducting line). This tool is usually run in combination with Gamma ray and termed as GR-CCL for accurate correlation.


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