Well Integrity Technical Section

Good day Great WITS Members

What is the best way to calculate MAASP for cemented annulus between two perforated casings where both were perforated for SAP curing and then squeezed with cement till lock up pressure and then scab liner covered the internal casing and the perforation interval.

Regards,

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Mostafa
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That is a great question. Without having the benefit of any of the details the easy answer is the collapse rating of the scab liner is your MAACP between the two casing strings. If pressure were to make its way to the perforations that the scab liner is covering it will be exposed to that pressure as a collapse load. If the scab liner has no internal pressure back up it could collapse, but likely take more than 100% collapse rating, depending on the wall thickness of the scab liner. Some are extremely thin and extremely easy to collapse and or split from collapse loading.

Mike Chaffin
Valence Operating Company

Mostafa,

I think Michael, has described the problem perfectly.  The collapse of the Scab liner is often lower than the original casing ratings.  And cement squeeze of the perforations rarely provides 100% isolation through the squeeze perfs. 

So I would consider the original SCP in the casing annulus as worst case. If you think the cement squeeze was successful you can reduce the risk by some percentage. This means you could have a larger differential pressure across the liner.  You will need to consider that during P&A. 

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Dan Gibson
aka The Well Doctor
Completion & Well Integrity Advisor
Houston, Texas
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