Alert
  • Published: 10 Jun 2024

Seal Assembly Retrieval Incident

Seal Assembly Retrieval Incident
Seal Assembly Retrieval Incident

Cause & Consequence

  • Uncontrolled release of a flammable gas or liquid

Description of Incident

A drill string was in the wellbore with a recovery tool to pull the 18¾” seal assembly, which seals between the top of the 9⅝” casing and the 13⅜” casing in the subsea wellhead. Historically, on occasion, there has been difficulty engaging the seal assembly with the recovery tool due to debris on the top of or within the seal assembly. Hence, normal practice is to wash the recovery tool into place.

Due to a desire to avoid getting debris in the chokes, this is done with the BOP rams / Annulars open and after the recovery tool is latched and before the seal assembly lock ring is disengaged from the wellhead the BOP Annular to be closed, allowing the well monitoring and corrective actions. As the recovery tool was washed down and was being landed, prior to reaching the desired set-down weight, the seal assembly unlocked from the wellhead.

This resulted in a liberation of some gas which had accumulated below the seal assembly. As a result, sea water from the riser was displaced onto the rotary table and the gas detectors below the rotary table & at the header box and in the shaker room activated. No other gas detectors were activated, indicating that the gas was contained within the areas that the water flowed. The well was shut-in on the lower annular preventer and monitored to confirm there was no pressure build-up.

Findings:

To unseat the seal assembly, the design is such that a small upward movement is first required to unlock the lockdown ring.

No such movement was initiated by the personnel involved and weight was being applied in a downward movement at the time.

The procedure in place, and which was being followed, was consistent with the recommended OEM procedure, with normal industry practice and with previous operations by the well operator. However, with this old style of seal assembly it is easier to release the lockdown ring than with the newer versions.

Key Learnings:

Since the design of the seal assembly system in wells of this era is fixed and it may not be possible to eliminate upward movement due to rig heave, the recommendation is that the procedure is modified. With similar seal assembly systems being recovered from floating rigs the annular should be closed before engaging the seal assembly with the MPT. Discussion with the parties involved will take place to finalise the precise procedure.

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