Shallow gas formation leaks represent one of the greatest hazards in the industry, especially when they manifest in mature wells where aging is affecting their cement insulation and surface facilities. These formations are normally covered by multiple strings that make it difficult to diagnose and access them.

Distributed temperature sensing (DTS) technology enables permanently installed thermal monitoring of the well, which, in combination with surface well manipulation, can identify temperature anomalies that lead to leak identification.

One of the critical requirements, especially in mature wells where permanent DTS installations are not available, is that the diagnostics are performed efficiently and, in many cases, with the smallest footprint possible.

A fiber-optic DTS line deployed using a slickline unit provides the benefit of a smart completion continuous monitoring with the minimal foot-print and efficiency of a slickline setup. The system employs a modular unit that can be used to perform all the associated slickline operations to prepare the well and then convey the fiber-optic line to perform the survey.

Two examples from offshore Sabah (Malaysia) are presented where completion and casing integrity issues were identified in conditions that would have not been possible by other technologies.

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