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BP application for consent to continue using Valhall QP denied

The Petroleum Safety Authority Norway (PSA) has turned down an application from BP Norge AS for consent to extend the operating life of the quarters platform (QP) on the Valhall field.


BP currently has permission to use Valhall QP for accommodation until 31 December 2014, and applied to the PSA for consent to extend this date to 31 December 2017.

The PSA takes the view that uncertainties are present in the analyses used by BP as a basis for its application to extend the operating life of Valhall QP. It has accordingly refused consent for continued use of the facility for accommodation.

Background
Valhall QP was taken into use on the field in 1980. According to the plan for development and operation (PDO) of Valhall, the design life of this installation was 20 years.

In order to continue using an offshore facility beyond its original design life, the operator must apply to the PSA for consent to an extension. The operator must then assess whether the facility has and can maintain its technical and operational integrity for the period of extended use covered by the application.

BP has applied for consent to extend the operating life of Valhall QP as an accommodation facility on several previous occasions.

  • 2007. Consent was given to extend its operating life to 30 September 2010.
  • 2010. Consent was given to extend its operating life to 1 September 2012.
  • 2012. Consent was given to extend its operating life to 31 December 2014.

These applications were primarily justified by the need for accommodation capacity on the field until the new Valhall PH process and hotel platform became operational, and for preparing and executing well work on Valhall DP. The PH facility became operational in January 2013.

Subsidence
Many years of oil and gas production mean that the Valhall reservoir has become compressed and the seabed has subsided. This subsidence means that the base of the topside on Valhall QP is nearer the sea surface than before, and no longer satisfies the air-gap requirements.

Valhall QP fails to meet the requirements for surviving a 100-year wave in occupied condition. BP accordingly has procedures in place for demanning when high waves are forecast.

Current status
The present consent expires on 31 December 2014. BP has applied for consent to continue using Valhall QP as a quarters platform until 31 December 2017 and thereafter as an end platform for escape and evacuation until it goes out of service.

BP wants to continue operating the facility with a demanning procedure for high waves, and will also shut it down from 20 December to 15 February in order to avoid one of the months with the greatest probability of high waves, and which experience has shown to be when destaffing is most frequent.

Uncertainty
The PSA has commissioned a team of experts from Sintef, Marintek, the Norwegian University of Science and Technology (NTNU) and external technical specialists. The reports from this work have been passed to BP.

On the basis of this work, the PSA has made BP aware of uncertainties related to the analyses used by the company as a basis for its application to extend the use of Valhall QP.

In particular, the PSA has challenged the following.

  • 100-year wave – height of the wave crest. In the PSA’s view, BP underestimates the crest, which means in turn that wave loads are underestimated in BP’s analyses.
  • Load from steep waves. BP’s analyses assume that the wave forms are symmetrical. In reality, they are asymmetrical where their crests are displaced in the direction of wave motion. Taking this effect into account increases wave loads.
  • Acceptance limit for ultimate limit state. The PSA considers the analysis method used by BP to be inadequate (a combination of ulimate limit state (ULS) and accident limit state (ALS), where ULS loads are analysed in relation to the requirements for ALS.
  • Determination of destaffing level. The assessments made by BP also influence the determination of possible demanning criteria in connection with bad weather.

A technical dialogue has been conducted with BP on regulatory requirements, the latest knowledge, and uncertainties related particularly to these considerations. The company has expressed understanding for the PSA’s arguments, but has chosen not to include identified uncertainties in the basis for its consent application. It thereby stands by the conclusions from its original analyses. In the PSA’s view, these considerations must be taken into account in order to comply with the regulatory requirements for load-bearing structures.

Decision
“BP is denied consent for continued operation of Valhall QP as an accommodation facility.

"In its analyses, BP has failed to define realistic acceptance criteria for non-linear analyses. The PSA considers that BP has underestimated the wave crest heights and the loads from steep waves. When determining demanning criteria, BP has failed to take account of higher-order waves and area effects. The PSA cannot therefore see that the company has fulfilled the requirements for analyses and for taking account of new knowledge and uncertainty, as specified in sections 16 and 17 of the management regulations on general requirements for analyses and on risk analyses and emergency preparedness assessments respectively. 

“Based on the information provided by BP, the PSA cannot see that Valhall meets an acceptable level of safety which finds expression in the requirements for load-bearing structures as specified in section 56 of the facilities regulations on load-bearing structures and maritime systems, with guidelines, see also section 11 on load/actions, load/action effects and resistance, with guidelines.”

 

Øyvind Midttun, Press contact
Email: oyvind.midttun@ptil.no | +47 51 87 34 77