Unexpected failure of the Rotating Control Device bearing rubber during a Managed Pressure Drilling operation caused a loss of well control event

Note: Original alert wording from IOGP Member Company.

While the Bottom Hole Assembly (BHA) was being stripped to the casing shoe, a sudden and total failure of the MPD RCD bearing rubbers occurred thereby causing a rapid loss of the Surface Back Pressure (SBP). This resulted in a loss of the primary well control barrier (Fluid Hydrostatic Pressure + SBP). After approximately 20 minutes the drilling crew was able to reestablish well control by restoring the Equivalent Circulating Density (ECD) to an overbalance condition. The BHA was then pumped to the shoe and maintenance activities conducted to replace the RCD bearing and continue with normal operations.

The MPD system was installed with a statically underbalanced MW in hole.

The BHA was being pulled, stripping back to the shoe with surface back pressure against the MPD RCD prior to pumping 2.07sg tripping mud from the shoe to surface. A Surface Back Pressure of ~1000psi was applied.

At 4780m a sudden and total failure of the MPD RCD bearing rubbers occurred resulting in a loss of the SBP and as such a loss of the primary barrier (fluid+SBP) for ~20mins. The well was monitored on the active, while the failure was investigated, before re-establishing drilling ECD to restore overbalance.

Then the BHA was pumped back to the shoe to change the RCD bearing. No gain volume was recorded but two gas peaks of 8% and 5% were circulated.

What Went Wrong?:

• Mechanical failure of the RCD bearing.
• Delayed response due to previous experience of only partial failures (still able to hold SBP).
• Confusion as to the best course of action due to - No significant reservoir drilled, no flow from the well on the active, tool joint passing the bearing at time of failure, sticking concern.

Corrective Actions and Recommendations:

• Delayed response – clarify procedures for bearing failure, the expected reaction is to shut the well in on BOPs Enhance drills with the crews during fingerprinting to cover bearing failure.
• Sudden and total failure of the RCD bearing can occur, the elements are particularly vulnerable under higher pressure stripping.
• The contingency procedures within the MPD programme for a bearing leak scenario focused on a manageable leak (able to apply SBP) and did not include specific steps to take in case of total failure.
• The operations team had not experienced a similar failure and therefore time was required to establish what had occurred. Note: No previous experience of sudden and total bearing failure.
• In long and stable operations a shift of risk-ranking and priorities can occur subconsciously, e.g. being stuck vs. well control.
• Full technical investigation of RCD element mechanical failure required. No cause identified yet.

Figure 1: RCD Bearing damaged - view 1

Figure 2: RCD Bearing damaged - view 2

Figure 3: Simplified Cause Tree Analysis

safety alert number: 317
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