Pulsed Eddy Current (PEC) based multi-casing corrosion evaluation can be classified into either multi-frequency non-collocated or time-domain collocated methods. Collocated sensors, having localized sensitivities, give a powerful time-to-depth (qualitative) corrosion distribution but suffer badly from eccentering and changing properties especially for late-time evaluation needed for three pipes and beyond [1]. Advanced processing [2-3] enables quantitative multi-casing evaluation using multiple spacings and multi-frequency non-collocated measurements but are challenged by casing and tool eccentering limiting maximum utilizable frequency for interpretation, and by ghosting effect (double indication of same heterogeneity) which limits its reliability near casing collars.In this work, using 3D finite-element modeling and advanced processing, we assess the performance of both measurement physics with a special emphasis on their sensitivities to casing properties (conductivities, permeabilities and thicknesses), pipe and tool eccentering, defect size, and vertically approaching heterogeneity in the context of evaluating four and more metallic pipes. In-house time-domain processing of collocated PEC measurements gives reliable inner two pipe thicknesses but cannot fully resolve the ambiguity in third pipe and beyond for arbitrarily corroded four and more centered casings. Processing the comparatively deeper non-collocated (multi-frequency) measurements gives excellent results for up to four centered pipes but a reliable quantitative evaluation requires advanced 3D modeling and processing workflows to fully disentangle the corrosion sensitivities from approaching heterogeneities and pipe eccentering—typically encountered while logging a multi-casing oil and gas well.&nbsp;References:1. Dutta, Sushant, Iqbal, Pervaiz, and Joseph Olaiya. "Multi-Sensor Time-Domain Electromagnetic Measurements for Quantitative Evaluation of Multi-Barrier Corrosion." Paper presented at the SPE Asia Pacific Oil &amp; Gas Conference and Exhibition, Virtual, November 2020. doi: https://doi.org/10.2118/202454-MS &nbsp;2. &nbsp;S. Omar and D. Omeragic, “Use of&nbsp;Apparent Thickness&nbsp;for Pre-processing of Low Frequency Electromagnetic Data in Inversion-based Multi-Barrier Evaluation Workflow”, the 44th Annual Review of Progress in Quantitative Nondestructive Evaluation, Jul. 2017.3. &nbsp;L. E. S. Martin, et. al., “New High-Definition Frequency Tool for Tubing and Multiple Casing Corrosion Detection”, Society of Petroleum Engineers, Nov. 2017. (SPE-188932-MS)

Comparative Analysis of Collocated and Non-Collocated Pulsed Eddy Current Sensing for Multi-Casing Evaluation

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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