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Slot recovery explained: extending the life of your offshore operations

Lifecycle stage
Late-Life

 

BACKGROUND

Drilled in the 1980s, a MAERSK well in the Tyra East field had suffered a misfortune when a large piece of downhole equipment had become stuck in it, preventing the well from being completed.

This would require Claxton to remove the BHA before any recovery could begin – a more complex operation than originally planned.

This is how Claxton went about the complex campaign…

INSPECTION

Claxton’s team visited the well in May 2013 to assess the situation and develop a recovery plan.

The BHA stuck in the conductor pipe was about 15 m long and had a diameter of 8–9 in. About 6–9 m of it was protruding above the seabed.

ASSEMBLING AN EXPERT TEAM

After working closely with Maersk to fully understand the challenges posed by the recovery operation, Claxton brought in the multidisciplinary team needed to deliver the project.

This involved close integration and collaboration with specialist cutting companies and a dive support vessel from Royal Boskalis Westminster NV.

PROJECT PROGRAMME

The programme started by deploying a specialist casing cutting system to remove a section of the conductor and leave the stuck BHA intact but exposed.

This approach called for modification of the cutting equipment and the subsea application of a system that is normally used on the surface.

Once the conductor was cut and removed, Claxton prepared a bespoke lifting device using an air hoist on deck deployed through an A-frame while divers clamped the lifting gear to the BHA.

The BHA was too heavy to recover in one piece and it was decided it would have to be cut subsea.

Two sizes of diamond wire cutting machine were used to cut through both the remaining conductor stump and the BHA simultaneously.

Once the cutting machine had sliced through the conductor and BHA, Claxton was able to recover the top section.

After the mechanical removal of the old casing was completed in the well, the slot recovery was completed by drilling a sidetrack well.

ENABLING THROUGH EXPERIENCE

Because it was hard to ascertain the final orientation of the ‘stump’ and remains from the BHA during planning, Claxton needed to create a unique whipstock.

The Claxton design team delivered a novel solution: The whipstock was fitted with a slot beneath the landing plate that would enable it to capture the exposed part of the BHA securely in any orientation.

The top half of the whipstock would rotate on this base and enable the new well to be kicked off in any direction. Claxton’s experience and knowledge of whipstock design was the key to providing an effective engineered solution.

RESULTS

The integrated team led by Claxton delivered the full work scope in only three months, including designing, manufacturing and testing the bespoke equipment. The cooperation between all partners made it possible to deliver what was needed in a very tight timeframe: the project was completed 4 days ahead of schedule, despite time lost waiting on weather.

CLAXTON’S EXPERIENCE

Claxton has invested in a unique spread of proprietary cutting and recovery tooling and has developed a cutting and recovery methodology that is field proven (over 282 cutting projects and counting), cost-effective and safe.

Slot recovery case study pack
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Slot Recovery Case Study Pack

Discover how Claxton’s engineers, machinery and methods have assisted with slot recovery operations all around the world in our case study pack.

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