An innovative electromagnetic tool is presented which utilizes transient or pulsed eddy current measurements to provide individual quantitative evaluation of downhole corrosion in up to four concentric pipes. Case studies from dual string completions are presented that compare the results from passes logged through short string (SS) and long string (LS) tubing. The novel instrument utilizes transient electromagnetics or pulse eddy current technology and contains three sensors that achieve a trade-off between high-resolution measurements of the inner barrier and high radial depth of investigation for up to five barriers. Each sensor induces coaxial outward-diffusing rings of eddy currents in multiple concentric tubulars and measures the consequent time-varying response. The full transient responses from multiple sensors are then interpreted to obtain individual tubular thickness profiles. Case studies are presented where the thickness profiles of outer barriers are obtained with the new tool. Logging was carried out in two passes; one pass was logged through SS tubing and the second pass was recorded through LS tubing. The comparisons show that the new electromagnetic instrument provides accurate corrosion evaluation while logging through tubing, even in the presence of a second tubing string. This feature of the electromagnetic tool is important for proactive well integrity management because electrochemical external corrosion, which is the primary corrosion mechanism in these wells, causes the outermost casing to fail first and then continues to penetrate inwards. Therefore, the new electromagnetic tool allows early identification of the outer tubulars with potential weak zones in the completion string without the need or cost of pulling completions for this purpose. This paper describes the advantages and limitations of state-of-the-art multi-sensor pulsed eddy current measurements for individual barrier evaluation of up to five concentric strings even in the presence of dual tubing strings. The presented case studies in dual completions support these conclusions, with additional evidence from other diagnostic tools.

The concept of the well double barrier envelope is a common industry practice and main philosophy of well integrity discipline. This is well-described in some of the international standards: API RP90 (1 & 2), Norsok D10, ISO 16530 (1 & 2). This double barrier policy applies to wells with positive pressure at surface capable to flow naturally. Primary barrier envelope consists of well equipment which is continuously under pressure and in direct contact with hydrocarbon. In case primary barrier element fails, secondary barrier envelope will be the one exposed to well media and holding the pressure. This content of this paper is related to such kind of wells that can flow naturally and should comply to the double barrier policy. Any failure in the primary barrier envelope (means - completion) normally is addressed during workover by simply re-completing the well with new completion (after retrieval of the old one). This can be done almost unlimited number of times, as long as there is a place to set the packer. Failure in the secondary barrier envelope (means - casing) can be repaired as well, but not that easy and very limited amount of time. In some cases, especially for onshore wells it might be economically more reasonable to drill the new well rather than to deal with complicated workover. Depending on the Company policy, casing integrity can be restored in sections using casing patches or the entire length can renewed by running and cementing casing of smaller diameter. Obviously, in both cases it impacts the size of the completion, further well objectives and cannot be done multiple times.