What we do

Challenge

DEME was appointed the Engineering, Preparation, Removal and Disposal (EPRD) contractor for the decommissioning of the damaged ‘Halfweg’ gas platform for Petrogas E & P Netherlands BV.

The normally unmanned Satellite Platform comprised a topside on four 54” O.D. legs that were secured into a concrete gravity-based foundation. Production at the facility ceased in June 2016 and plug and abandonment was completed in 2017. The platform subsequently suffered severe structural damage at the end of 2017 after being struck by a ship. Damage was caused to both the topside and the legs.

Solution

Our preparations for the removal involved visits to the platform to conduct detailed structural analysis to ensure that the topside could be lifted safely.

In mid-December 2018, the HLJV ‘Apollo’ was mobilised to the site. Once the HLJV was jacked-up next to the platform, “a making safe” operation was executed to enable the crew working safely on the platform. Prior to lift off of the topside, it was necessary to reinforce the topside first and then perform a procedure for separating the platform from the legs. For that purpose specially designed reinforcement beams were pre-fabricated and installed offshore.

Used technology

Offshore installation vessels

When we had completed the preparations, the topside was hooked-on to the HLJV 'Apollo' crane hook and separated from the legs by means of abrasive water jet cutting. Once the topside was safely on the deck of HLJV ‘Apollo’ and seafastened, the legs were cut one by one subsea above the foundation by means of a diamond wire cutting tool. During the cutting operation, the legs were suspended in the HLJV’s crane hook. Upon completion of the cutting operation, the legs were lifted on deck of the HLJV and down-ended and sea fastened on the deck for transportation to shore.

The topside and legs were transported on deck of the HLJV to the disposal yard in Flushing. Ultimately, an impressive 98% will be recycled.

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