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Providing assurance on effectiveness of annulus seal

The Challenge
A customer required valuable log data to demonstrate to legislative authorities that a cement plug was in good condition and providing an effective seal in the annulus prior to abandonment of a well.

The cement plug had previously been set in the well, covering both the tubing and annulus. The cement within the tubing had been removed by milling, with the intention of logging the cement remaining on the outside of the tubing, i.e. within the annulus, as required by local legislation.

These were challenging conditions for interpretation as the cement logged was contained between a tubing and a casing string, whereas such tools would usually be used to evaluate cement located between a casing string and the surrounding formation.

The Solution
Faced with this challenge, we ran a logging survey using the Radial Bond Tool (RBT).

The RBT survey was able to successfully detect cement within the annulus and we were able to pinpoint the depths at which the cement was detected.

The Results
The survey highlighted one area showing a very good bond between the tubing and cement, indicating that the plug had likely formed a hydraulic seal within the annulus at this point.

We were also able to provide our client with critical information regarding areas where cement to tubing bonding was poor, and other areas where the bonding was better.

The results and analysis provided the client with the knowledge that an acceptable interval of high quality cement existed within the tubing annulus, allowing them to demonstrate full compliance with local legislation and to proceed with the well abandonment.




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