Statoil completes report on Gullfaks C incident

Guntis Moritis
OGJ Production Editor

HOUSTON, Nov. 5 -- Statoil handed over to Norway’s Petroleum Safety Authority a report on the incident that occurred on May 19 during the drilling of Well 34/10-C-06 AT5 on the Gullfaks C platform off Norway.

Statoil said the incident was caused by a leak in the 13 3/8-in. casing that reduced the number of barriers in the well and resulted in a 2-month shut down of the production from the platform while the barriers were restored. The incident did not involve any injuries to personnel or environmental damage, but the company estimates that the event caused a loss or delay of production with a value of 1,084 million kroner and other financial losses of 677 million kroner.

Statoil used managed pressure drilling to drill Well C06 to a 4,800-m measured TD. The report indicated a hole developed in the 13 3/8-in. casing during the final circulation and wellbore cleaning of the reservoir section, leading to a subsequent loss of drilling fluid to the formation. This loss of back pressure then led to fluid influx from the reservoirs until solids or cuttings packed off the well at the 9 5/8-in. liner shoe. The pack-off limited further influx of hydrocarbons into the well.

The report said the hole in the 13 3/8-in. casing resulted from insufficient technical integrity of the casing as well as from inadequate monitoring of the pressure in the C annulus between the 13 3/8-in. casing and the 20-in. casing that allowed a leak in the 13 3/8-in. casing to develop into a hole. This pressure had increased during the weeks before the incident but was not noticed, the report said.

The report also noted that a contributing factor in the length of time to restore the barriers in the well was that the managed pressured drilling operation had an insufficient margin between the pore and fracture pressures.

The investigation team recommended that for Gullfaks operations Statoil should:

• Develop new acceptance criteria for managed pressure drilling.

• Review the conditions for managed pressure drilling.

• Coordinate requirements and best practice for managed pressure drilling.

• Update pressure prognoses.

• Document that the shear ram is capable of cutting the drillstring.

• Change the shift relief plan for drilling supervisor and toolpusher.

• Review the procedures for communication and mustering with the second-line emergency preparedness organization.

• Verify requirements related to managed pressure drilling in procedures for work process management and implement changes as required.

• Clarify requirements related to risk management in the well construction process.

• Clarify requirements related to involvement of Statoil expert and support environments.

Contact Guntis Moritis at guntism@ogjonline.com.

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