NEWS: REL has presented a technical paper at the Nuclear Decommissioning Conference in Manchester on the 12th May 2010 CLICK HERE ---

Engineering/Planning

Data Review

The accuracy of the data supplied for review prior to the engineering and planning directly effects the results of the planning and cost estimation.

A thorough knowledge of the installations is required in order to enable the accurate planning and scheduling of the decommissioning activities. This includes information on design, construction, installation, sustained damage, equipment or structural modifications and operating history parameters. In order to achieve the required accuracy to the cost estimates, a substantial amount of preliminary and historical information is required.

Preparation for Disposal

This engineering phase includes all activities for preparing for the removal of the platforms. Activities here include installation surveys, re-instatement of lifting lugs and severing of connections.

Removal of Platform/Offshore Installation

This activity will assume that the platform or offshore installation has been left cold and will commence with the mobilisation of removal equipment to site. The removal/ dismantling operations will be examined on a case-by-case basis and will be undertaken by the safest and most cost effective method for that installation. Possible renoval method include :

suitable heavy lift vessel
piece small for topside removal
Buoyancy for jacket removal
New lifting technology i.e. Versatruss Bottom -Feeder, Pieter Schelte etc.
Toppling and placement for artifical reefs (Not Possible on OSPAR Region)

The scope of the removal operation will be as follows:

Hook-up and remove the decks
Internally cut the piles below the seabed using abrasive waterjet equipment or other suitable cutting system
Remove the jackets
Transport to shore

Marine Operations

All marine spread, personnel, marine support, subsea cutting, lifting, securing and transporting activities will be planned and estimated. This phase will deem to be complete once the installations arrive at quayside.

Marine operations planning and costing for offshore installation deommissioning have become more complex in recient years as new lifting/dismantling technologies have emerged.

The marine operations depend on the removal technology used to dismantle the platform/installation and each platform/installation is unique and should be considered on a case-by-case basis. Crane vessels are the most common method of removal of offshore platforms worldwide but there are other technologies and methodologies emerging. The use of these new technologies have lead to the development of specific marine operations. Current possible removal method include :

suitable heavy lift vessel (HLV)
piece small for topside removal
Buoyancy for jacket removal
New lifting technology i.e. Versatruss Bottom -Feeder, Pieter Schelte etc
Toppling and placement for artifical reefs (Not Possible on OSPAR Region)

All of the above new technologies withe the exception of the Pieter Schelte, (which is under detailed sesign at present) have been used to remove offshore installations. So now realistic verified cost estimates can be determined with confidence.

The general approach for the removal of the platform/installation can reflect use of these technologies. It is assumed that to optimise the cost of removal, through flexibility of the contractor’s removal schedule, that the number of contracts placed would be kept to a minimum. Typically for removal by SSCV the ‘window of opportunity’ that would be required to optimise cost would be at least a year. The envisaged sequence of facilities removal and disposal will be as follows:

• Following well abandonment and the production system being shut-down and made hydrocarbon-free. Phase 1 of the preparations for removal would be undertaken using a platform-based crew ahead of mobilisation of the removal spread.

• If platform removal is awarded to a HLV operator the removal would be undertaken in conjunction with the operations to remove the topsides structure by the HLV. If other removal methods are used the the appropiate engineering and planning would be prepared. For example if Versatruss was to be used, the vent tower would have to be removed, by say specialist proven climbers experts who have developed a removal system of dismantling in sections.

• Mobilisation of the removal spread and Phase 2 of the preparations for removal would be undertaken with the removal spread or a support vessel alongside the platform.

• Removal of topsides structure using SSCV or Versatruss or piece small etc. For removal by SSCV/HLV suitable vesselswould be identified capable of undertaking the specific removal. If for example, Versatruss was to be used two specially prepared cargo barges with the required number of booms per barge for this lift. Piece small operations may require a jack-up for installations with small reinforced deck area. The Pieter Schelte, when built, will also require the topsides to be prepared to use this technology.

• Removal of jacket structure, including piles cut at a target of up to 5m below seabed level (depending on local regulations), using a HLV or buoyancy or a combination of HLV and buoyancy or Versatruss or . Due to the nature of the lift, the maximum lift attempted would be approximately 80% of the rated lift capacity. For removal by SSCV there are four vessels identified capable of undertaking the removal, which are operated by two contractors, Heerema and Saipem. Smaller capacity crane vessels may also be able to undertake the work by sectioning the structure to suit the lower lift capacity. Alternatively the Versatruss jacket handling frame will be used or the Pieter Schelte, both will also require the topsides to be prepared differently to use their technology.

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