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The inspection of wellbore casings has been extensively investigated owing to the increasing concern for safety in oil and gas production. However, efficient techniques for inspecting asymmetry defects have not been achieved. In this study, we developed a uniform circular array (UCA) to address the problem of borehole pulsed eddy current (PEC) techniques for asymmetry defect inspection in downhole casings. Based on the borehole PEC system model, the UCA developed with multiple independent probes was designed to achieve asymmetry defect inspection, and the three-dimensional magnetic field data of borehole depths, circumferential azimuths, and sampling times could be obtained. Furthermore, a multichannel data acquisition circuit, which guarantees downhole operation at 150 °C, was developed for the synthesized UCA. Using azimuth dimension information from the synthesized UCA at a certain borehole depth, we obtained an inspection approach for the width and penetration depth of asymmetry defects in the circumferential and radial directions, respectively. Simulations and field experiments were conducted, and the results demonstrate the effectiveness of the proposed method in inspecting asymmetry defects.

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Pulsed eddy current (PEC) is a widely utilized technology for the nondestructive inspection of industrial tubes and pipes due to its rapid and accurate results. To improve the longitudinal resolution of PEC, multiple transmitting coils (MTCs) are used to realize magnetic focusing. However, this approach is difficult to apply to narrow downhole environments because of the complex transmitting array and electrical circuits. To address this issue, we present a synthesized transmitting coil (STC) that combines MTCs into a single coil with multiple connected sections using different winding directions and number of turns to adjust the magnetic field distribution. A theoretical derivation was presented for the analysis and interpretation of the magnetic field, and a figure of merit (FoM) was constructed to optimize the STC parameters. Numerical simulations and experiments were performed to validate the proposed STC for downhole casing inspection, and the experimental results showed good agreement with the simulation results.

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