Time-Domain Electromagnetic Measurements Aid Evaluation of Multibarrier Corrosion

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202454,“Multisensor Time-Domain Electromagnetic Measurements for Quantitative Evaluation of Multibarrier Corrosion,” by Sushant Dutta, Pervaiz Iqbal, SPE, and Joseph Olaiya, Baker Hughes. The paper has not been peer reviewed. A time-domain electromagnetic tool is presented that is capable of quantifying four barriers individually and inspecting a fifth barrier qualitatively. The new tool uses time-domain electromagnetic (TEM) or pulsed-eddy-current technology, which has become a recognized technique for individual quantitative tubular-corrosion evaluation in multiannular well systems (multiple concentric tubulars) in recent years. The novelty of the tool is its ability to exploit the information-rich wide-band-pulsed excitation using three sensors that enhance the sensitivity to multiple barriers. Physics of Time-Domain Measurements The TEM tool described in this paper belongs to the broad family of electromagnetic induction tools. Induction tools use a transmitter coil to generate a time-varying magnetic field that induces a time-varying electric field (and hence eddy currents) in the surrounding media. The secondary magnetic field generated by the eddy currents is proportional to the spatial electrical conductivity. A receiver coil measures the time derivative of the secondary magnetic field. Conventionally, induction tools often operate on a time-harmonic (continuous wave) excitation at one or more discrete frequencies.