As well integrity is of utmost importance for personnel safety and environmental interests there is an ever increasing need for tools and systems that verify and confirm the status of wells with suspect integrity. Recent near-surface, outer casing failures caused by external corrosion on relatively new wells in the Kuparuk Field of Alaska prompted research for a non-invasive predictive method to foresee failure and aid repair prioritization. There are a variety of tools and methods available to locate leak points and corrosion inside of tubulars, but very little literature exists concerning external corrosion and damage detection on outer and middle concentric strings of casing. The following method is a valuable qualitative approach used to determine existence and severity of shallow external surface casing corrosion before leaks occur. The technique uses a logging tool that analyzes the variations of metal thickness within three concentric sets of down-hole tubulars and identifies areas where metal loss exists. The metal loss combined with assumed or known internal tubing condition reveals the wells with the highest risk for shallow surface casing leaks. When a high risk area is discovered proactive excavation repair plans can be made before any safety or environmental problems occur. This paper summarizes the tool, technical approach and assumptions, limiting factors, and the remarkable comparison between the metal thickness logs and the actual external surface casing corrosion observed on 12 wells after excavating each up to 27 ft in the Greater Kuparuk Area. Future plans and strategy using the technique are also discussed in the paper.
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