Abstract

Well integrity monitoring is growing in importance as fields' mature, as oil and gas is exploited in evermore hostile and corrosive environments and due to stricter regulatory requirements. Over the lifetime of a typical well monitoring the completion integrity includes running logs such as cement bond evaluation, production flow logs and tubular inspection. Casing and tubing integrity monitoring often consist of a combination of mechanical multi-finger caliper logs, Electro-Magnetic (EM) pipe thickness logs, Ultrasonic casing inspection logs and down-hole video. These direct inspection logs can be used to monitor corrosion early and help mitigate serious leaks or well failures. When combined with other logs that can indicate abnormal flow conditions such as temperature logs, spinner profiling and passive noise detection logs can assist diagnosis of completion problem that would need intervention.

Electro-Magnetics 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 down-hole 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 a 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 innermost 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 forward analytical model tied to experimental data acquired with an actual logging instrument. The forward model is used to ensure optimum tool design and allow development of suitable algorithms to process field data. This is followed by a field case study which demonstrates how this PEC based slim tubing-casing inspection tool can be utilized in combination with other techniques such as multi-finger calipers. We conclude with some pointers to further development of the hardware and data processing techniques.

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