The current practices to monitor Tubing-Casing Annulus (TCA) integrity involves applying a sustained pressure with inhibited fluid in the annulus space. This is to allow for a positive indication of pipe integrity. In such cases where integrity is lost, it is challenging to diagnose or pinpoint the exact leak source. Because of the current limitations in the assessment procedures, inaccurate diagnostics can result, which can lead to expensive and time consuming operations and deferred production.
Well-A is a single string well drilled as a vertical oil producer. The well has undergone several work-over operations and was recompleted as a single string observer many years ago. After being healthy for a long period, it was reported in recently that this well was suffering loss of TCA integrity. In addition, the tubing was reported to have an obstruction above the packer, and the master valve was in a partial stuck-open position. Since diagnosing downhole problems will allow for a safe, optimized and long lasting remedy job, it was decided to run High Precision Temperature (HPT) and Spectral Noise Logging (SNL), to assess the integrity of the TCA, and identify the source of the leak. The investigation was carried out rig-less, prior to moving the rig, to reduce time and optimize cost.
The results showed that the loss of TCA integrity was due to a casing leak, and confirmed the packer and seals integrity. This useful information eliminated the necessity of securing the reservoir below the packer, reducing costs and saving one week of rig time. In addition, proving that no communication existed between the reservoir and the TCA prevented sidetracking the well, which would have resulted in incurring a significant cost and about 1.5 weeks of rig time.
The evaluation of well integrity envelopes throughout the life cycle of a well is essential to ensure a safe operation while maintaining optimum production without causing environmental damage such as aquifer contamination. Behind casing flow and loss of annuli integrity poses a challenge to operators, therefore regular evaluation would provide valuable information to monitor the asset's integrity and program required well interventions in a timely manner.
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