The Miller field in the central North Sea was operational for 15 years (1992 to 2007), during which time it produced some 345 million barrels of oil equivalent. The Platforms final decommissioning in 2018, has been an innovative and successful project, with the safe preparation and removal of the topside modules (circa 28,000 t) and a derogated jacket (circa 12,000 t).
This paper focuses on the removal of one of the Miller topsides modules using the innovative "Extended Lift" method, which utilised the Saipem S7000 crane vessel to carry the structure to the disposal yard in Norway (see Figure 1) for direct offload to the quayside. The challenges and key issues covered in this paper are listed below.
First extended lift (circa 60 hours transit) of a large structure in air (circa 5000 t)
Module was lifted with the vertical flare boom in place
Tank tests (1:50 scale models of S7000 and module) were carried out to verify the dynamic clearances to vessel cranes and to establish operability limits (wave heights and periods)
Correlation of the model test results with analytical parameters
"Go or No-go" Decision Criteria
Vessel operations and contingency planning
Motions Monitoring System employed for the duration of the lift and transit
As part of the conclusion of the paper, we will present why Saipem considers the "Extended Lift" as the safe and cost effective method of choice for both platform modules and substructures.
The Miller topsides module in question comprised:
M5 Wellbay module (~4920t)
M8 Flare attached to M5 (~380t, 163m above sea level - was the tallest structure in the North Sea)
Following the removal from the Miller platform offshore, the module was delivered to the specialist facility in Stord, Norway for final deconstruction and disposal. The main reasons for adopting the "Extended Lift" method are explained below.
Firstly from a safety point of view, the separate removal of the Flare would entail access onto the tall structure to inspect, prepare and rig the lifting gear. Such access would expose personnel to the associated risks of having to work at great height on an aging structure.
Secondly the removal of this flare represented very weather sensitive operations, which would significantly impact the critical path schedule for the heavy lift vessel offshore. Both this time impact and the above personnel risk were eliminated by the controlled "toppling" of the flare at the disposal yard (Figure 1.1).
