The objective of this document is to present the experienced gained by the industry in the
period 1998-2002 in a “state-of-art” review of the technical challenges and other assessment
issues considered in order to identify the best disposal option for disused offshore concrete
gravity substructures within the OSPAR Maritime Area.

The objective of this document is to present the experienced gained by the industry in the
period 1998¨C2002 in a ¡°state-of-art¡± review of the technical challenges and other assessment
issues considered in order to identify the best disposal option for disused offshore concrete
gravity substructures within the OSPAR Maritime Area.

OSPAR Decision 98/3 provides the regulatory framework for decommissioning all off-
shore structures. In respect of gravity based concrete structures the Decision states that
¡°The dumping, and the leaving wholly or partly in place, of disused offshore installations
within the maritime area is prohibited¡±, but adds that ¡°¡­if the competent authority of the
Contracting Party concerned is satisfied that an assessment ¡­shows that there are significant
reasons why an alternative disposal¡­is preferable to reuse or recycling or final disposal on
land, it may issue a permit for¡­a concrete installation…to be dumped or left wholly or partly
in place¡­¡±. The part of the concrete platform where such alternative disposal options may
be assessed would be the concrete substructure; ie the load bearing structure supporting the
topside facilities. No derogation possibility exists for the topside facilities.

There are altogether 27 concrete platforms located within the maritime area of the OSPAR
Convention, in Norwegian (12), British (12), Dutch (2) and Danish (1) sectors of the North Sea.

Between the adoption of Decision OSPAR 98/3 and July 2002, decommissioning of 4 concrete
platforms has been considered. Related studies have been carried out and completed
and they represent most of the knowledge gained by the industry since 1998.

The two North Sea operators who have presented decommissioning proposals on behalf of
the their co-ventures, have considered the following main disposal options for four disused offshore concrete platforms:

  • Removal for onshore disposal
  • Removal for deep water disposal
  • Partial removal (cut down the structure down to -55m to respect the IMO Guidelines)
  • Leave in place

This report highlights the main findings on the four key elements in the comparative assessment of each disposal option:

  • Technical feasibility
  • Safety for personnel
  • Environmental Impact
  • Cost

ªôis review identifies several uncertainties associated with the removal of both first and
second-generation concrete gravity structures such that a case-by-case evaluation will be
required to assess the specific circumstances for each installation. The first generation of
offshore concrete gravity platforms installed in the 1970s were not designed or constructed
for future removal operations. Although provisions for removal were incorporated into the
design of later, second-generation concrete platforms, these may not be fully effective because
the obstacles to and hazards associated with removal were not appreciated.

An important development over the period of this review has been the introduction of a
comprehensive programme of consultation involving a wide range of stakeholders, experts
and other users of the sea to view the question of decommissioning from as many angles as
possible. This consultation and engagement process has been pivotal in arriving at balanced
conclusions in respect of the major decommissioning activity that has taken place between 1998 and 2002.

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