Carrying the load - Part One

In its hunt for ever more hydrocarbons, the offshore upstream industry has continued to push boundaries few in the early days of the industry would ever think could be pushed.

One such development is floating LNG (FLNG) – the production of remote natural gas fields, deep beneath the sea, using subsea production equipment on the seabed, tied into floating production vessels, which also serve as LNG production units for offtake using tankers to international markets.

While the concept has been around since the 1970s, few have been able to make it happen, until now. Shell has been leading the charge with its Prelude FLNG, vessel, which will be stationed offshore Australia, and is due on stream in 2017. Malaysian national oil firm Petronas is nipping at Shell’s heels to be the first FLNG operator with its own smaller vessel, to be used offshore Malaysia. Others are following suit, including Australia’s Woodside, which just went into front end engineering and design (FEED) on its Browse Basin project, with plans for three FLNG units, based on a similar design to Prelude.

These mighty ships, often converted tankers stripped of their engines to make way for process and storage facilities, will, however, need at some point to be moved. As the upstream offshore oil and gas industry makes its first enormous step into FLNG, heavy transport vessel operator Dockwise has made its first steps into transporting ship-shaped FPSOs in a move that will pave the wave for transporting both more FPSOs as well as the fledgling FLNG fleet, giving the designers of these assets options they have not had in the past.

Case study

The Dockwise Vanguard, the largest heavy transport vessel in the world, arrived in Southeast Asia with its first ship-shaped floating production storage and offloading (FPSO) cargo, Bumi Armada’s Armada Intrepid.

This is a groundbreaking job for a vessel that had only just completed the transportation of ENI Norge’s 107 m dia., 64 000 t, Goliat Sevan-design cylindrical floating production and storage unit from Hyundai Heavy Industry’s (HHI) shipyard in South Korea to Hammerfest in Norway.

The 110 000 t capacity Dockwise Vanguard’s next major job will be Total’s 85 000 t, 250 m long x 60 m wide Moho Nord floating production unit (FPU), which will be transported from HHI’s yard in Ulsan, South Korea to West Africa in early 2016.

Being able to transport FPSOs using a heavy transport vessel offers FPSO operators and owners a faster and safer alternative to the current industry norm – wet tows using tugs.

The Armada Intrepid FPSO onboard the Dockwise Vanguard.

Safe loading

The Armada Intrepid, previously known as the Schiehallion FPSO while it was working for BP, west of the Shetland Islands, UK, was safely and successfully loaded onto the Dockwise Vanguard in Rotterdam’s Caland Canal on 8 May, just eight days after the heavy transport vessel’s arrival in port.

The job of loading and transporting the Armada Intrepid posed some interesting and unique challenges, due to the dimensions of the cargo. This was the first ship-shaped FPSO to be transported on the Dockwise Vanguard. Weighing 60 000 t (42 000 t plus ballast), it is one of the top three heaviest cargoes ever transported. That, in combination with its ship-shape, makes this project interesting.

Unlike normal loads, which are positioned on the Dockwise Vanguard’s 275 m x 70 m deck by ballasting the vessel beneath the water line and floating the load across its beam, the Armada Intrepid, which is too long to float across the beam, had to be floated over the deck via the Dockwise Vanguard’s stern, carefully slotting between the two aft casings, with just 2.5 - 3 m leeway either side.

Removing one of the aft casings could have been an option, however due to the time and costs involved in carrying this out, and the ability to take the Armada Intrepid through the stern, the team opted for the latter method.

This loading configuration required more handling (tugger and tow lines) compared to normal jobs, due to the careful manoeuvering involved. Getting the water depth and tidal window right was key, making loading location and timing crucial.

Part two of this article is available here: 'Carrying the load - part two'

Written by Taco Terpstra and Hans C. Leerdam, Boskalis, the Netherlands. Edited by Callum O'Reilly

Read the article online at: https://www.lngindustry.com/liquid-natural-gas/24082015/carrying-the-load-1185/