PSA Investigates Well Kick on Valhall DP

Valhall Field, North Sea
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On December 10, 2003 a kick occurred in well 2/8-A-8 B on Valhall DP. Another such situation occurred in the same well one week later. The Petroleum Safety Authority Norway (PSA) has investigated these incidents. The investigation report was sent to BP Norge AS on September 16, 2004.

Well control was gradually regained during December 2003, after a period of worsening and pressure build-up in the well and annulus.

The wellbore path (A-8-B) was then plugged and prepared for a new sidetrack / new wellbore path (A-8-C).

Summary of the investigation report:

The investigation indicates several direct causes of the incident and the worsening situation before well control was regained.

The direct causes of the incident/worsening situation were:

1. Drilling in permeable hard formations in an area that was expected to be depressurized.

2. Loss of mud to the formation in greater volumes than experienced in other Valhall wells.

3. Worsening of the situation in connection with running the drill string in/out, as well as circulation of the well without closing the BOP.

4. Plugging of the drill string due to "gunk".

The investigation shows that the underlying causes of the kick are multiple and complex and cannot be linked to a common factor/system. This applies e.g. to the following:

  • Well design not sufficiently documented and potential problems with pressure classification of 13-3/8" casing not taken into account.
  • Circulation of well fluid for well control with open well for a long period of time without closing BOP.
  • Ambiguous mandate, responsibility and communication between land and offshore.
  • Insufficient manning at the beginning of the well control incident.
  • Insufficient understanding of the risk associated with permeable hard formations with free gas.
  • Contact between water and material for lost circulation "gunk" in the drill string.
  • Deviations from BP's internal procedures.
  • Lack of quality assurance in connection with the use of perforation equipment.
  • Lack of overview over where the well influx was coming from.

  • We would like to thank all of the involved parties in BP who have been very accommodating in connection with the investigation.

    We have asked BP for the company's evaluation of the proven deviations and observations by October 15, 2004.

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