01 April

Decommissioning Project

Charter of DSV ‘Siem N-Sea’ for the provision of vessel based surface diving services.


N-Sea was contracted by the client to carry out a decommissioning project with additional IRM works.  There was a requirement to provide assistance to the rig with decommissioning preparation works on three subsea trees.  These works included but were not limited to cleaning, barrier testing and attaching required rig equipment.

Additional IRM works were scheduled and completed during decommissioning scope down time.



  • Late award of contract
  • Weather and tidal conditions in Southern Sector
  • Relatively deep diving depths for surface diving
  • Limited structure and tree information
  • Working with/alongside/under the rig
  • Addition of IRM scopes
  • Critical schedule restrictions



Appreciating a drive for cost reductions with our client, N-Sea offered a cost effective diving solution offering considerable advantages over the expensive saturation diving alternatives.  Utilising surface oxygen decompression techniques allowed N-Sea to reach required depths without the heavy cost burden of saturation diving and reduce the overall cost of the project significantly with limited impact to schedule.



  • Project was completed on time and within budget.
  • Cost effective approach maintained throughout project
  • Effective communication and working relationship between the SIEM N-Sea and the rig.
  • Positive feedback from HSE diving inspectors following offshore trip
  • N-Sea commended for adaptability, flexibility and drive to complete scope


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