Negative Planning LL with Wellesley

Carmen (35/10-10S) – Reservoir section

What happened:

Drilled 8 1/2″ section with 5 7/8″ DP with 1400-1500 lpm and low ROP, saw ECD up to 18 points. MW was 1.72 and ECD measured to 1.88 sg.

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What was planned:

Use 5 7/8″ DP for the whole section drilling 8 1/2″ hole. Simulations drilling 8 1/2″ using 5 7/8″ DP with 1.85 sg with 1500 lpm flow rate and ROP of 20 m/hr gives ECD of 10 points to 1.948 sg.

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What was learned:

Higher than simulated/expected ECD observed that may cause fractures. Loss/gain situation for the deepend section in 8 1/2″ section (4050-4089 m MD).

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What actions are required:

Use of tapered DP string, using 5 7/8″ and 5″ will decrease ECD with some points. Has to be simulated to see difference. But just some few points decrease might have a big difference, may for example never experience loss/gain situations.