Abstract

Tubular inspection can be split between direct measurements such as caliper logs or downhole video observation and Electromagnetic (EM) methods that measure properties sensitive to pipe thickness, with wall thinning associated with corrosion and other pipe defects. Various EM methods have been reported over the years often initially for pipeline inspection and then adapted for downhole well monitoring. These methods include Magnetic Flux Leakage (MFL) and Eddy Current (EC) measurements. Early EM methods were single frequency but later developments include multi-frequency. In this paper we report an emerging technique called Pulsed Eddy Current (PEC) which is inherently multi-frequency and in time domain is radially sensitive which enables inspection of multiple tubular thicknesses. Most inspection techniques including some EM methods are only capable of inspecting the inner most tubular or only the total thickness of multiple tubulars. However, a PEC tool can measure separate thicknesses of both inner and a second tubular. This allows quantitative corrosion evaluation of casing without removing the completion tubing.

The paper covers a theoretical review of the PEC technique and development of a fast forward analytical model tied to experimental data acquired with an actual logging instrument. The fast forward model is used to ensure optimum tool design and allows development of an inverse model which realises quantitative evaluation of the corrosion within multiple tubulars from field data.

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