An electromagnetic corrosion inspection tool was designed to accurately assess corrosion in as many as five nested pipes. This paper provides details of the principles of operations and the methodology of the algorithms used for data processing of this tool.

This tool uses the eddy current principle and includes two transmitters and eight receivers. It operates in continuous wave mode at multiple frequencies. Optimized transmitter-receiver spacing configurations and multifrequency operation provide sufficiently diverse information to help assess the metal loss in each individual pipe for a wide range of configurations.

The performance of the tool was validated with synthetic and actual data by using controlled tests and experiments. These tests demonstrated the accurate determination of the defect positions and metal loss in each individual pipe of a multiple configuration. To validate the wide operational range of the tool, synthetic tests were used that included challenging scenarios, such as the identification of defects with a total metal thickness of all casings of more than 2 in. or overlapping defects at the same axial position. Finally, the accuracy of the tool in practical scenarios was verified by using results from well tests. The electromagnetic corrosion inspection tool has delivered unprecedented accurate assessments of the fourth and fifth pipes, as well as an accurate assessment of the first, second, and third pipes.

The information provided by this tool can significantly improve decision-making for mature well operations, especially in areas with high corrosion rates, and could result in significant cost savings to the operator.

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