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The PSA's investigation of the gas-blowout on Snorre

Summary report:
On 28 November 2004, an uncontrolled situation occurred during work in Well P-31A on the Snorre A facility (SNA). The work consisted of pulling pipes out of the well in preparation for drilling a sidetrack. During the course of the day, the situation developed into an uncontrolled gas blow-out on the seabed, resulting in gas under the facility. The Petroleum Safety Authority Norway (PSA) has completed the investigation report.

Personnel who were not involved in work to remedy the situation were evacuated by helicopter to nearby facilities.

The work to regain control over the well was complicated by the gas under the facility which, among other things, prevented supply vessels from approaching the facility to unload additional drilling mud.

After having mixed mud from the available well fluid chemicals, this was pumped into the well on 29 November 2004, and the well was stabilized.

With the well stabilized and the gas flow stopped, the work to secure the well with the necessary barriers could commence.

The PSA characterizes this incident as one of the most serious to occur on the Norwegian shelf.

This is because of the potential of the incident, as well as comprehensive failure of the barriers in planning, implementation and follow-up of the work on well P-31A. Only chance and fortunate circumstances prevented a major accident with the danger of loss of many lives, damage to the environment and additional loss of material assets.

The consequences of the incident are costs related to delayed production, comprehensive and time-consuming work to secure the well, normalization and start-up of the facility.

Surveys of the seabed after the incident revealed several large craters near the well template and near one of the fastening anchors for the Snorre A platform.

Three months after the incident, production of oil and injection of gas/water had still not returned to normal levels. There were no physical injuries in connection with the incident.

Snorre A (source: Statoil)

SNA (photo) is an integrated living quarters, drilling and production facility permanently anchored to the seabed with tension legs. Under the SNA is a well template with 42 wells with risers and several export lines. Total production from SNA is approx. 200,000 bbls/day.

Under slightly different circumstances, the incident could have resulted in (1) ignition of the gas and (2) buoyancy and stability problems, with resulting danger of the loss of many lives, damage to the environment and additional loss of material assets.

On 29 November 2004, the PSA appointed an investigation group to chart the course of the incident, identify potential breaches of the regulations, as well as propose use of policy instruments and recommendations for additional follow-up. The mandate included circumstances up to when the well pressures in P-31A were stabilized at 10:22 a.m. on 29 November 2004.

A task force was also designated to monitor the normalization work.

The investigation group has interviewed relevant personnel from the land organization and on the facility, evaluated the submitted documents and conducted an inspection on the facility. An MTO (man-technology-organization) diagram to map direct and underlying causes was prepared to assist in analyzing the incident.

The regulations require technical, operational and organizational barriers that both prevent serious incidents from occurring and that they escalate. Serious failures and deficiencies have been uncovered in all phases of Statoil's planning and implementation on well P-31A.

These relate to:

  • Failure to comply with controlling documentation
  • Deficient understanding and implementation of risk assessments
  • Deficient involvement of management
  • Breach of well barrier requirements.

The non-conformities relate to failure on the part of both individuals and groups in Statoil and with the drilling contractor. The non-conformities occurred at several levels in the organization on land and on the facility.

The investigation shows that the list of non-conformities and items that could be improved is extensive. Therefore, there is nothing to indicate that the incident was caused by chance circumstances.

The non-conformities found in the investigation would all have been intercepted and corrected if the barriers had functioned.

Individual barriers fail from time to time, but failure of so many barriers in different phases of an operation is extremely rare.

The PSA is critical of the fact that such an extensive failure of the established systems was not uncovered. We question why this was not discovered and corrected at an earlier point in time.

Contact in the PSA:
Inger Anda
Press spokesperson
Tel. +47 970 54 064