01 August

Bleo Holm and Arbroath Diving Nitrox Campaign

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Scope of work

Charter of DSV ‘Siem N-Sea’ for the provision of vessel and daughter craft based nitrox diving services and WROV at Bleo Holm FPSO and Arbroath Platform.


N-Sea was contracted on behalf of Talisman Sinopec Energy UK Ltd to provide air diving services to the Bleo Holm FPSO and Arbroath Process Platform.


At the Bleo Holm FPSO N-Sea were required to fit a blanking plate and cofferdam arrangement to facilitate internal valve repairs. N-Sea also installed a bend restrictor to the Blake umbilical, this was a requirement due to the existing bend stiffener having slipped several meters.


At the Arbroath Platform N-Sea were required to carry out HP Water Jetting and Grit Blasting in preparation for then carrying out Non Destructive Testing on 4 x caisson guides.  Nylon wedges were installed at these caisson guides with dimensional checks being undertaken on 2 x conductors and their guides to determine a suitable course of action for designing and installing shims at a later date.


One of N-Sea’s Daughter Craft, Aberlour, was utilised for the diving at the Bleo Holm and was moored alongside the FPSO with the Siem N-Sea serving as a mother vessel. Diving works at Arbroath made use of the vessel based system onboard the Siem N-Sea using extended umbilical (Golden Gate) techniques with the contingency of Daughter Craft Diving when required.



  • Diving within congested Turret Location amongst Risers and Mooring Chains and working with differential pressures.
  • Varying Depths of works
  • SIMOPS with Heading Control Tug
  • Large umbilical excursion distance from vessel stand off to Arbroath platform centre.


  • Exemplary attitude to safety shown by project teams and client representatives, with all safety tools used to good effect to ensure works were completed without accident or incident.
  • Experienced on site management and supervision ensured that the air /nitrox mix selection provided safe efficiencies and also that gas transfers of the various air / nitrox mixes were conducted and controlled as per N-Sea procedure.

  • Good clear concise communications and understanding between all interfaces – FPSO, Daughter Craft, Heading Control Tug and Siem Stork with detailed bridging documentation.

  • The Siem N-Sea’s impressive extended umbilical diving capabilities permitted access beyond the platform centre from the east face meaning all diving works could be undertaken by the vessel system removing any need for daughter craft intervention.


N-Sea completed all original scopes as well as additional on location requests without accident or incident, on time, within budget and to the satisfaction of all stakeholders.

The performance of the offshore project teams and N-Sea’s vessel’s and equipment received commendations from TSE UK subsea project team.


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