DECK ELEVATION PROJECT FOR OIL PLATFORM FIELD SUBSIDENCE

41,000 tonne lift across 6 platform complex.
Largest lift in the world at the time.

88 x 700 tonne jacks
18 x 180 tonne jaks
17 x 3000 litre HPUs
170 x 1500 litre HPUs
25 x 600 litre HPUs

Overview

The Ekofisk ‘Jack Up’ project was one of the most difficult and demanding offshore engineering operations ever attempted at the time. The platform discharged 200,000 barrels per day to the Phillips complex at Teesside, making this internationally significant project a local one for IMH.

Due to seabed subsidence, the Ekofisk complex in the North Sea was sinking by approximately 40cm per year. This had reduced the safety air gap between the platform decks and storm waves from 20m to 16.3m.

To compensate for the subsidence across six platforms, the ‘Jack Up’ project was developed to extend the platform legs and raise the decks by 6m, restoring the clearance required to accommodate a 23m, 100-year design wave.

The Offshore Platform Jacking Challenge

The scale of the project presented a significant engineering challenge. All six platforms needed to be raised simultaneously because of the existing bridges and pipelines connecting the complex.

The operation involved an oil platform lifting requirement of almost 41,000 tonnes, making it the largest lift in the world at the time. The overall project had a value of £400 million and represented one of the most challenging projects undertaken by IMH Commissioning Engineers at that time.

Careful coordination of the offshore platform jacking operation was essential to ensure the interconnected structures in the oil & gas sector could be elevated safely and simultaneously.

Hydraulic Platform Lifting System

The lifting method involved cutting the platform legs before powerful hydraulic jacks were clamped into position to raise almost 41,000 tonnes of platform structure.

The extensive hydraulic platform lifting system included 88 x 700 tonne jacks and 18 x 180 tonne jacks, supported by a substantial network of hydraulic power units. These comprised 17 x 3000 litre HPUs, 170 x 1500 litre HPUs and 25 x 600 litre HPUs.

Together, the hydraulic equipment enabled the six-platform complex to be lifted simultaneously while accounting for the bridges and pipelines connecting the individual structures.

Raising the Ekofisk Platform Complex

Once the platform structures had been hydraulically raised, 6m support spools were fitted into the resulting gaps in the platform legs.

This allowed the decks to be permanently elevated by 6m, restoring a safer degree of clearance between the platform complex and the sea below.

The operation addressed the reduction in safety air gap caused by ongoing seabed subsidence and provided the additional clearance required for the 23m design wave criteria.

Project Outcome

The Ekofisk ‘Jack Up’ project successfully delivered a 41,000 tonne lift across the six-platform complex, making it the largest lifting operation of its kind in the world at the time.

For IMH’s Commissioning Engineers, the project represented one of the most technically challenging and rewarding projects the team had undertaken, demonstrating the role that large-scale hydraulic systems can play in complex offshore platform lifting and elevation projects.

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