This paper presents the results obtained from the application of high-fidelity distributed measurements and station logs for well integrity assessment in a gas producer. Historical well data suggested the presence of sustained annular pressures attributed to the migration of gas across a leak point on the tubing. The primary objective of this survey was the assessment of the upper completion interval to identify potential leak sources and investigate any defect on the casing and tubing.

A joint well integrity survey was done via a retrievable, hybrid fibre-optic sensing-based service deployed through the tubing together with a Multi-Finger Caliper (MFC) and Electro-Magnetic Defectoscope (EMDS) to evaluate the tubing profile and integrity of the Wireline Entry Guide. Given its adaptability to third-party wireline and electromechanical tools, the hybrid fibre optic cable was deployed in the well, alongside the MFC and EMDS, with zero interference effects. Real-time data analytics were performed onsite, thus informing key decisions during the survey.

The leak detection program originally designed for this survey included two main monitoring periods; the baseline period to serve as a reference and a period of annular venting to create a higher-pressure differential across the tubing to stimulate the leak. However, shortly after the well was shut-in, there was a sharp decline in the annulus pressure, even before the annular wing valve was opened. A decision was made to cancel the annular bleed-off, as zero psi was recorded. Acoustic signals detected across the tubing during this period were related to cable and fluid movement during well stabilization. This conclusion was further corroborated by the MFC and EMDS log as the tubing section was found to be in a relatively good condition from top to bottom with very light corrosion across all joint (within the maximum penetration range from 0% to 30%). The Wireline Entry Guide was also found to be in a good condition without any significant damage and visible vertical crack. The temperature and acoustic responses detected across the reservoir interval were, however, indicative of ongoing crossflow during the shut-in period. It appeared that the middle reservoir zone was acting as a source, dumping gas into the bottom zone.

The unique data solution provided by the fibre-optic sensing technology allowed for continuous and wide coverage logging of the well. Real-time data displays of the entire wellbore, together with the point sensor measurements, led to a more comprehensive well diagnostics outcome.

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