OGJ Senior Staff Writer
HOUSTON, May 23 -- Norway’s Petroleum Safety Authority (PSA) gave Norske Shell AS until June 1 to outline plans to improve well intervention and well control procedures following an oil well maintenance error in Draugen field that risked an oil leak into the Norwegian North Sea last year.
PSA said the incident involved a wireline operation to replace a gas lift valve on well 6407/9-A-01 on Dec. 4, 2010. Shell was the well’s operator, while Seawell AS was the contractor for the wireline operation.
To replace the gas lift valve, the subsurface safety valve must first be extracted from the well. As the subsurface safety valve was pulled through the christmas tree, it became stuck and the upper master valve was blocked, meaning only one barrier remained against an oil leak.
Workers restored normal well barriers on Dec. 8, 2010. PSA said crews ran the subsurface safety valve back into the well and inserted two mechanical bridge plugs in the well above the subsurface safety valve. The other christmas tree valves were closed, pressure-tested, and accepted.
“The incident did not result in any injury to personnel,” PSA said. “The scope of material damage in the christmas tree was not known at the time of the incident, however, the incident involved major accident potential.”
Acknowledging it’s impossible to establish fail-safe methods for preventing things from getting stuck in the christmas tree during wireline operations, PSA said, “Correct understanding of the risk that may be expected can contribute to prevent the loss of well barriers if something gets stuck.”
Investigators identified several serious breaches of the regulations, saying nonconformities involved inadequacies in management, risk assessment, well barriers, well barrier sketches, well control, and daily reporting of drilling and well activities.
PSA issued Shell a notification of order and said Shell is to notify PSA when the order has been complied with regarding what PSA called “a serious well incident.”
PSA instructed Shell in a Mar. 29 letter outlining an investigation into the incident, “We also request that Norske Shell assess the appropriate involvement of Seawell AS in its follow-up of this case.”
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