1 Overview

Electro-magnetic Thickness Instrument is used to measure the thickness of downhole metal pipe, which can reflect the corrosion degree of casing. The sensor array of the instrument is composed of 16 (12) independent sensors. Every sensor can get a curve of casing thickness.

2 Operating Principle

The tool generates an alternating magnetic wave, which propagates out of the tool and permeates through the casing. Once outside the casing, the wave travels a short distance along the length of the pipe, before re-entering the well bore in order to complete its path. It is in this region, where the magnetic wave re-enters the well bore, that the sensor array is positioned. Each sensor then detects localized information about the magnetic wave that has traveled through the casing wall.

The velocity and amplitude of the emitted wave are affected by the thickness of metal through which it has traveled. Greater metal thickness results in slower wave propagation and greater attenuation. As a result a sensor that is adjacent to an area of thinner metal will receive a wave of greater amplitude some time before a sensor that is adjacent to an area of thicker metal. The differences can be used to locate and quantify variations in metal thickness along the tabular.    

3 Applications

Inspection of tubing and casing for internal & external metal loss.

Measures absolute wall thickness.

3D visualizations provide powerful qualitative images of well conditions

Detects pitting and gradual metal loss.