Design and Research of Differential Probe for Oil Casing

Abstract

Pulsed Eddy Current (PEC) testing is a vital non-destructive technique for assessing corrosion in oil casings, yet its practical application is often hindered by severe interference from lift-off variations and limited detection sensitivity in complex downhole environments. To address these challenges, this study proposes an optimized differential PEC probe system integrated with high-permeability Ni-Zn ferrite cores. A three-dimensional transient magnetic field model was established to investigate the detection mechanism and optimize key structural parameters. Simulation results demonstrate that the proposed differential structure effectively suppresses common-mode noise induced by dynamic lift-off fluctuations, achieving a signal-to-noise ratio improvement of over 22 dB compared to traditional absolute probes. Furthermore, through collaborative optimization of the magnetic core dimensions and coil geometry, the probe’s sensitivity to defect signals was enhanced by approximately 2.2 times. The study also reveals a robust monotonic non-linear relationship between the differential signal peak and defect depth, with a fitting accuracy exceeding 0.98, confirming the system’s potential for precise quantitative evaluation of corrosion severity. These findings provide a solid theoretical foundation and design framework for developing high-performance downhole inspection tools, significantly advancing the reliability and accuracy of oil casing integrity assessment.