This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 194269, “An Advanced Technique for Simultaneous In-Situ Inspection of Multiple Metallic Tubulars,” by Yanxiang Yu, William Redfield, SPE, Nicholas Boggs, Kuang Qin, Marvin Rourke, SPE, and Jeff Olson, SPE, GOWell International, and Mosunmola Ekije, Fluor Federal Petroleum Operations, prepared for the 2019 SPE/ICoTA Well Intervention Conference and Exhibition, The Woodlands, Texas, USA, 26–27 March. The paper has not been peer reviewed.

A new pulsed-eddy-current (PEC) electromagnetic (EM)-based tool called an enhanced pipe-thickness-detection tool (ePDT) has been introduced for the corrosion inspection of multiple pipes. The tool can measure the metal wall thickness of five concentric pipes with a maximum outer diameter (OD) of up to 26 in. This capability, along with the tool’s unique configuration, provides an advanced downhole solution for tubular evaluations of production, injector, and storage wells.


As hydrocarbon production and storage wells age and new production and storage wells are exposed to elevated concentrations of corrosive fluids, well-integrity monitoring is gaining more attention. These factors have influenced well-performance, safety, and environmental concerns. Early, periodic monitoring of tubular corrosion and other defects can reduce the risks of serious leaks or well failures in a cost-effective way.

Historically, the continuous sinusoidal-signal-based far-field eddy-current (FFEC) technologies have been developed and deployed for multiple-concentric-pipe average-thickness measurements. However, FFEC is adversely influenced by the strong interference of direct excitation signal transmission coupling and the EM skin effect; this reduces the pipe response because of a decreasing signal-to-noise ratio (SNR) that does not allow quantitative evaluation of more than two concentric pipes.

In contrast, the PEC-excited EM signal contains wideband frequency components from kilo-Hertz to sub-Hertz range. The low-frequency EM signals penetrate concentric metal pipes effectively. The induced PEC on each tubular has different initial amplitude and decay rates because of a combination of OD, thickness, and EM parameters. After excitation, magnetic-field changes triggered by a combination of mutual inductive interactions among the pipes, eddy-current diffusion, and damping are picked up by the receiving coil during the acquisition window. Research and field applications have proved that the PEC method is more reliable for average thickness detection in multiple pipes. In previous studies by the authors, three pipes with up to 17-in. OD can be detected by magnetic tools. However, because of the combination of high signal dynamic range, inadequate SNR, extraneous tool motion, and troublesome interference of pipe magnetization, it has proved difficult for these tools to quantify thicknesses of outer pipes reliably in the presence of more than three concentric tubulars or at ODs greater than 17 in.

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