Downhole detection tool

A method of detecting a downhole cable or control line running along an external wall of a well casing, comprising the steps of:

• providing an eddy current sensor and locating the eddy current sensor in proximity to an internal wall of the well casing,
• wherein the eddy current sensor includes a receiver coil and a transmitter coil, where the receiver coil and the transmitter coil are configured in a nested arrangement,
• sending a pulse of current to the eddy current sensor, thereby generating a magnetic field, and creating eddy currents in the well casing,
• measuring, using the eddy current sensor, the magnetic field generated by the eddy currents induced within the downhole cable or control line,
• moving the eddy current sensor around the circumference of the internal wall of the well casing,
• repeating the generating and measuring steps,
• analysing the measurement results of the eddy current sensor, including:
• processing the readings taken by the eddy current sensor,
• monitoring a decay of the magnetic field induced by the eddy currents generated by the electrical pulse,
• analysing a tail end of the magnetic field response curve of the eddy current sensor readings during the decay, wherein the analysis identifies any readings which present a profile suggestive of the downhole cable or control line;
• and
• providing an indication of where the downhole cable or control lines are detected at an outer wall of the well casing on the basis of the decay of the magnetic field created by the eddy currents, and
• recording the location corresponding to any such indications of where the downhole cable or control lines are detected.