Decommissioning the Ninian Northern platform

Project summary

PD&MS Group provided a range of decommissioning design and engineering services for the topside removal preparation of a 40-year-old oil platform.

The background

The Ninian Northern platform is an oil facility in the North Sea, located in the East Shetland Basin between the Shetland Islands and Norway. The Ninian Field contains three platforms: Ninian Northern, Ninian Central and Ninian Southern.

The Ninian Northern installation was a steel jacket platform located 3.2 miles north-west of Ninian Central in water 141 m deep. It was installed in June 1978 and was designed to operate as a satellite to Ninian Central, passing well fluids to it directly, although it was also equipped to partially process the well fluids.

RSK Group company PD&MS Group was contracted by Allseas to support the Ninian North Topsides Removal Preparation Project. The scope involved completing all necessary modifications to facilitate the topsides removal by the Allseas Pioneering Spirit heavy lift vessel and included the following activities:

• lift point installation – installation of 16 Allseas-supplied bearing blocks onto the jacket legs to engage with Pioneering Spirit horseshoes to perform the lift.
• K1 leg brace – additional scope identified late in project – this was required to strengthen the lift point due to concerns over the identified lift weight.
• removal of obstructions for single lift – the destruction and removal of escape-to-sea ladders and platforms adjacent to the jacket legs to accommodate Pioneering Spirit
  equipment sea fastening – securing loose items to prevent the potential for dropped objects during the lift.
• derrick sea fastening – securing the derrick in a centralised position prior to the topsides lift
• cutting and sea fastening of pipework – this involved a significant number of risers, j-tubes, conductor guide sleeves and caissons, some of which required the removal of internals prior to air-gapping underdeck, followed by partial removal again as required to facilitate the topsides lift.

The challenges

Project timescale

This fast-tracked project was kicked off in November 2017, with engineering and implementation completed by April 2018.

Weather conditions

Offshore implementation of the project was severely impacted owing to weather conditions from November 2017 to January 2018.

Additional work requirements

As the project unfolded, additional needs were identified, which increased the scope of work.

Safety concerns

When working with ageing infrastructure, additional safety concerns are likely to arise due to the age of the materials.

The solutions

The PD&MS team used an agile approach to the project and emphasised collaboration between the onshore and offshore teams. This meant that PD&MS was able to work around the different challenges while ensuring the work was completed on schedule.

There were in excess of 15,000 hours’ work completed with no lost time injuries.

The impact

Thanks to PD&MS’s agile working practices, it was possible to deliver the project on time and with an overall project saving of 40%.