Gamma Ray / CCL Tool（GR‑CCL）

General Description

The Gamma Ray / CCL Tool is a combined depth‑reference instrument widely used in production logging. It integrates a gamma‑ray detector and a Casing Collar Locator (CCL) within one single tool housing. This combination provides depth correlation for all downhole logging measurements, and is routinely included in every PLT tool string.

Gamma‑Ray measurement detects natural gamma radiation emitted from formation rocks. Logged GR curves are matched against open‑hole gamma‑ray logs for formation correlation and depth calibration. The CCL utilises electromagnetic induction principle to identify metal casing collars. Distinct magnetic signal anomalies are generated when the tool passes casing joints, producing sharp deflection peaks on logging traces for casing depth marking.

Working Principle

Gamma‑Ray Section

Scintillation detector captures natural gamma rays from surrounding formations. Gamma‑ray intensity is converted into count‑rate pulses. The count rate reflects shale content of the penetrated formation. By correlating with original open‑hole gamma log, log depth can be anchored to known formation markers.

CCL Section

The CCL consists of transmitter and receiver coils. Alternating current energises the transmitting coil to build magnetic field. As the tool moves past casing collars, the change in casing metal thickness modifies magnetic flux, inducing voltage variation in the receiving coil. These characteristic voltage spikes represent casing joint positions for depth control.

Key Features

◆Dual‑function integrated design, provides both formation correlation and casing joint depth marking.

◆Reliable depth reference for production logging, injection profiling and downhole diagnostic surveys.

◆Enables depth matching between cased‑hole PLT data and historical open‑hole logs.

◆Compact outer diameter, easy to concatenate with flowmeter, pressure‑temperature and holdup tools.

◆Works in casing, tubing and sand‑screen completions, compatible with wireline, slickline operations.

Typical Applications

◆Depth calibration and depth anchoring for all production logging runs

◆Formation correlation between cased‑hole logs and open‑hole baseline logs

◆Locating casing collars, perforation intervals, packers and downhole completion hardware

◆Verifying tool position relative to perforations during PLT, injection profile logging

◆Monitoring depth shift caused by cable stretch during downhole operations

Typical Technical Specifications