Negative Cement LL with DNO

Canela (6507/7-16 S) – Surface section

What happened:

Cement slurry was changed to a gas-tigh slurry due to encountering shallow gas in pilot hole. Due to fracture margin and risk of losses only the lower part og the slurry was converted to a gas-tight slurry as not possible to convert lead slurry to gas-tight. Gas bubbles were observed at sea bed when cement started setting up. Most likely from interval where gas tight cement was not used.

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What was planned:

Cement the 20″ casing to seabed using regular G-cement slurry.

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What was learned:

A regular G-cement tail slurry required a lot of chemicals to make the lsurry gas tight vs. a light weight cement.

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What actions are required:

Evaluate to use a light weight cement slurry for cmenting the top holes to easier enable conversion to a gas tight slurry. If drilling in area with potential for shallow gas evaluate to plan holes with gas tight cement/foam cement.