Quantitative Corrosion Assessment with an EM Casing Inspection Tool

Abstract

Abstract A recently introduced electromagnetic (EM) casing-corrosion evaluation tool provides total metal thickness, tubular internal diameter, and defect imaging inside single and multiple casings. Quantitative assessment of ongoing corrosion enables timely mitigation strategies to prevent leaks, environmental damage, or catastrophic failures. This slim tool allows measurements through production tubing, eliminating the risk and saving the cost of tubing removal. It provides a high-resolution casing assessment. EM assessment uses magnetic fields from induced eddy currents to determine the casing thickness and the inner casing diameter. Receiver coils mounted along the tool axis receive these EM fields to give average metal loss; small pad sensors on 18 arms around the tool perimeter provide an image of local metal loss. The measurement resolution is determined by propagating laboratory-measured noise to uncertainty in the computed casing thickness. These calculations are verified with numerical simulation and field validation. Advanced signal processing converts the raw data to high-quality logs. Deghosting removes the double responses seen as a defect first passes by the receiver coils and later by the transmitter. Several field examples show the quantitative, high-resolution assessment of pipe condition. Log examples show detection of casing joints, multiple casings strings, and the presence of corrosion damage in the low- and high-frequency images.