The lifting of the 950 tonne Fram Vest process module is the heaviest lift to a loosely anchored, semi-submersible floating production platform on the North Sea that has been carried out. This complicated operation required meticulous planning, including specific module tests.
Fram Vest will come onstream in October next year. Two subsea frames at 360 meters depth will each have four wells that are linked to the Troll C platform 20 kilometers away. The daily production of 60,000 barrels of oil from Fram Vest will be processed in a separate module on Troll C.
The process module was lifted on board Troll C in May this year by means of the lifting vessel "Saipem 7000" which lay in dynamic positioning, while Troll C was loosely anchored. The module was placed with the highest level of accuracy on three supports over the winch house on the aft port column of the platform.
“We have been highly focused on ensuring that the lift would be carried out in a safe and controlled manner,” says Halfdan Knudsen, client’s representative for Fram Vest.
Not much model testing of North Sea lifting operations has been carried out in recent years. But as this lift was so unusual, and as both the lifting vessel and Troll C would be afloat, model tests had to be run.
Ståle Øvretveit, who is Hydro’s project manager for model testing at Marintek’s sea basin at Trondheim, explains that over 100 lifting and positioning attempts were made using different wave directions and heights.
Marintek also carried out computer simulations of module and vessel movements to document the forces at play during the lift.
An information video, including the model trials in Trondheim, was used to train the personnel taking part in this advanced lifting operation.