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Dropped object with potential for injury - riser release

Country: UK - Europe

Location: OFFSHORE : Mobile Drilling Unit

Incident Date: 1 July 2021   Time: 08:00

Type of Activity: Drilling, workover, well services

Cause: Dropped objects

Function: Drilling


Following running of the completion in a subsea well drilled from a Jack-up Mobile Offshore Drilling Unit (MODU), it was necessary as per the well programme to recover the 16" Riser. While recovering the 16" Riser to surface, a drill-pipe deployed anchor tool, which was set inside the riser, prematurely released at around 35K lbs overpull, rather than the 114K lbs rated overpull, dropping the Riser (45 ft) and causing damage to the Subsea Wellhead Housing (WHH) sealing face. The anchor tool had been pull tested to 40K lbs to confirm engagement prior to releasing the riser.

What Went Wrong?:

The load rating of the drill-pipe deployed anchor tool in operation was not as per advised value and subsequently failed when a relatively modest load was inadvertently applied.

Corrective Actions and Recommendations:

Damage to wellhead sealing face was sustained, which was subsequently addressed and confirmed satisfactory. It is recommended that during recovery of casing or riser, the slip mechanism of the anchor tool is energised constantly by applying pressure and that the shear pins and ratchet mechanism are not solely relied upon as a means to ensure tool engagement.

Figure 1: Drill-pipe deployed anchor

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Figure 2: Riser

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Safety Alert number: 334
IOGP Safety Alerts http://safetyzone.iogp.org/

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