www.heerema.com

Turning concepts into reality!

Successful engineering and fabrication of large and complex structures for the offshore oil and gas industry demands not only fabrication and facility operating expertise, but also a fabrication-driven engineering focus to ensure on-time delivery within budget. At our fabrication location Heerema Zwijndrecht we completed the largest offshore deck ever built in the Netherlands. The picture shows the 11,000 tons Integrated Production & Hotel Facility topsides for the BP Valhall Re-Development project during the load-out operation on a seagoing barge. Heerema’s Zwijndrecht facility has a capacity which ranks amongst the largest indoor facilities in Europe. At Heerema Fabrication Group we are turning concepts into commercial reality: from conceptual design to final fabrication and delivery.

Heerema Fabrication GroupNoordweg 83336 LH ZwijndrechtThe NetherlandsTel: +31 [0]78 - 625 04 25E-mail: info@hfg-heerema.com

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A HEEREMA COMPANY

CYAN MAGENTA YELLOW BLACK

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Dutch knowledge is called in when the going gets tough

Dutch contractorsinvest en masse

Modern customers want full-service provision

New semi-submersible Type O Super Vessel

Building excellencefor complex projects

F3-FA platform is a unique construction

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SpecificationsThe production time for the F3 gas field is estimated at eight years, but the platform itself must have a use-ful life of at least twenty years. The platform’s maximum production capacity is 3 million cubic metres of gas a day, 3,450 barrels of condensate and a maximum of 150 cubic metres of water. Two wells will be connected to the platform, with an option for a third. The gas will be discharged via a 10-inch diameter pipeline connected to the existing pipeline infrastructure in the F3 block. The extracted gas is brought ashore in the Netherlands, at Callantsoog. The platform offers accommodation on board, for a crew of 18. As well as local operation, the platform can also be controlled and monitored remotely, from Centrica Energy’s G6 production platform. Compared with the previously men-tioned Calder platform, the F3-FA platform has been designed far larger and heavier, is installed in deeper water and must handle far more difficult wind and sea conditions. The topsides is 50 metres long, 30 metres wide and 30 metres high, and weighs in at more than 4,000 tonnes. The footprint of the complete platform, with conven-tional and suction piles, measures 63 by 45 metres, and the structure reaches a total height of 133 metres. Each of the four suction piles weighs 440 tonnes, is 13 metres high, and has a diameter of 15 metres. According to HFG’s project manager Frank Slangen, in total, the complete platform weighs 8,800 tonnes and the design and fabrication took in excess of 1 million man hours.

The F3-FA gas production platform

installed offshore.

It was already widely known that the lead-up to the F3-FA project had involved a FEED (Front-End Engineering Design) study in the period April through to August 2008. During this study, it was determined whether the gas field in ques-tion in the F3 block of the Dutch sector of the North Sea could be developed on the basis of a SIP-2 concept. SIP stands for Self-Installing Platform, in other words a platform that can be installed offshore without needing to call upon the services of a large crane vessel and heavy pile-driving equipment, but simply using a transport barge, a lifting system of strandjacks and suction piles. In this case, however, far larger versions of each of these systems had to be used than employed in the two previous occasions on which self-installing platforms were deployed, including the installation of the platform in the Calder field in the Irish Sea, in 2002. On that occasion, the platform, weighing 680 tonnes, had to be installed in just 29 metres of water. Its topsides measured 20 metres long by 16 metres wide, and it was equipped as a marginal gas production platform.Shortly following completion of the FEED study, Centrica Energy decided that it would employ the SIP-2 concept. Against that background, an EPCI contract was signed in February 2009 with the Heerema Fabrication Group (HFG) as main contractor and fabricator, and with Iv-Oil & Gas and SPT Offshore as part-ners. Alongside the offshore installation using a transport barge, the platform had to fulfil one other key requirement: it had to be possible at a later stage to easily remove the platform from the field for subsequent redeployment in either the Dutch or the British sector of the Dutch Sea.

F3-FA platform is a unique construction

Project involving major technical challenges

A reusable platform supported on the bed of the North Sea with four large suction piles, on which the complete topsides is suspended from superbolts. This is the best description of the new F3-FA gas production platform operated by Centrica Energy. However, what at first glance appeared to be a simple upscaling of a previously employed self-installing offshore platform in fact turned into a true R&D project that really pushed the boundaries of what is today possible in terms of steel technology and mathematical computing. The relief when the platform was finally firmly anchored on the seabed of the F3 block at the start of September 2010 was correspondingly great. Nonetheless, this successful conclusion was preceded by a considerable volume of preparatory work.

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“To solve the node problem, we chose to remove them entirely from the deck for the time being, and to reinstall them once the fabrication of the top-sides was completed. The water depth restrictions meant that the clamping system for the deck had to be raised higher.” According to project engineer Fedor van Veen, the SACS programme was used for the static calculation, in combination with an ANSYS model. The results were tested by a work-ing group at the Delft University of Technology and by Lloyd’s as certify-ing body. “All in all we very much pushed at the boundaries of what is possible in terms of steel technology and mathematical computing.”

Superbolts One unique element of the design is the way in which the entire topsides is attached to the four legs. Wim Bal

continued: “On top of the legs, we produced a massive construction. A sort of yoke, with bolt holes. In these, 6 metre-long bolts with a diameter of 240 millimetres are suspended, each weighing 2 tonnes. These are known as superbolts. There are four such bolts on each leg. Each bolt is preten-sioned to 1200 tonnes. Even the nuts weigh 300 kg each. The entire topsides is therefore suspended on sixteen superbolts. Another unique element is the design of the clamp connections. These are sort of half shells that were put in place after the platform had been installed offshore. These clamps, attached to the main deck, were filled with specially-manufactured rubber blocks. 20 blocks, each weighing 250 kg, were placed in every clamp. The use of these rubber blocks prevents the moment loads applied to the legs being transmitted into the deck. The rubber simply absorbs the peak loads.

The site move of the F3-FA deck at

the HFG yard in Flushing.

The 6 metre-long superbolts from which the

complete topsides is suspended.

HeadachesWim Bal, managing director of Iv-Oil & Gas explained: “During the design stage, it rapidly became clear that this was more than a relatively simple up-scaling of the initial SIP concept. The process section was not the problem. That was based on a concept tried and tested on numerous occasions on the North Sea. The real headaches were reserved for the strength management for the platform construction.” Nor-mally speaking, the jacket of a plat-form consists of legs, strengthened by braces. The result is a relatively rigid structure. In the case of the F3-FA platform, the four legs without braces are subjected directly to the force of the waves, which in turn generate further forces on the topsides. “As a consequence, the normal methods for strength calculation were practi-cally useless – a situation that was in fact not discovered until well into the process. We then decided to try out an FEM analysis on the basis of which the entire platform could be modelled. As it turned out, in the deck alone there were just under one thousand connections, known as nodes. We then attempted to place these nodes into seven categories. After carry-ing out about 200 load cases on each of the points, a matrix emerged that had to be thoroughly calculated.” The initial problems the designers came up against involved the contradictions in static and dynamic loading. The static load problems could easily be solved by using more steel in the structure. But in this case, the dynamic loads were so great that in fact less steel had to be used. While the calculations went on, work on fabrication was started at the HFG yard in Flushing.

Drawing of the new F3-FA reusable

gas production platform operated

by Centrica Energy.

Fabrication of the four 13 metre-

high suction piles, each weighing

440 tonnes.

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Transport and installationThe partners also gave careful con-sideration to the transport operation. According to managing director Mark Riemers of SPT Offshore, respon-sible for transport and installation, a MOSES model was used for calculat-ing the transport forces. Model tests were also carried out in the towing tank at MARIN. For transport to the F3 field, considerable water depth was necessary because viewed from the top, the four 13 metre-high suction piles hung more than a metre down into the water. The operation therefore required a total draught of 14 metres and a total width of 63 metres. In-cluding grillage and securing devices, the total transport weight was 10,150 tonnes. “To secure the legs, extendable beams weighing 2,100 tonnes were fitted to absorb the vertical forces, in combination with an 1,850 tonne fork construction to absorb the horizon-tal forces. On 18 August of this year, the transport barge headed out to sea. The Boa Barge 35 was towed by the Norwegian tugs BB Worker and BB Server. On the outward journey to Flushing, these tugs had already installed an anchor pattern in the F3 block, to allow the barge to be moored immediately upon arrival on site. The journey out to the F3 block took almost four days. Once on site, however, conditions proved too stormy, and the barge had to return to shore. Because of the draught, the initial plan was to use Rotterdam as safe haven. How-ever, the authorities refused to allow the transport into the port. The storm strengthened to a force 9 gale, with waves of up to 6 metres in height.

After a 24-hour wait, we were eventually allowed to enter the port. Upon inspection, it fortunately emerged that the platform had suffered no damage whatsoever.”

Once the storm had died down, a second attempt was made. Because the two Norwegian tugs were assisted in this second operation by the far more powerful Bourbon Orca, the outward journey time was shortened by ten hours, representing a reduced weather risk. On 1 September, the transport arrived in the F3 block, for the second time. “Using the strandjacks, we lowered the legs in three hours and it took just another six hours to subse-quently simultaneously fix all four suction piles in position. The topsides was then released from the Boa Barge 35, and lifted up into position. When the barge was pulled away, the most precarious part of the operation in terms of weather risk was concluded. During the night of 2 to 3 September, at 1 a.m., precisely two days and four hours after arrival in the field, instal-lation work was concluded.”

Following commissioning, the drilling rig Noble Scott Marks drilled the first production well, and just after New Year, the first gas was produced from the field. The first gas delivery represents the successful conclusion for HFG, SPT Offshore and Iv-Oil & Gas of a challenging project that imposed severe demands on the partners, but at the same time generated considerable knowledge for future projects.

Pancake methodAs in numerous other construction projects, this topsides was also built using the pancake method – in other words, deck by deck. This work was undertaken by the HFG yard in Flush-ing. Overall project manager Frank Slangen explained: “The topsides was built in our construction hall. A start was made on the work in September 2009 and following the site move of the module on platform trailers to an outdoor location, the four 75 metre-long legs were installed, using a 1,300 tonne crane. At one point, we had ten cranes travelling around the yard to ensure that all the installa-tion work was completed on time. The 4,000 tonne deck was subsequently lifted using strandjacks to install the grillage on the underside, neces-sary to ensure solid support for the topsides on the transport barge. The grillage was 6.7 metres high, and in total weighed 800 tonnes.” It is also worth recording that the risers for the production wells travel through one leg, while the gas transport pipeline passes through another. The leg even includes a second pipeline for an optional additional connection.Frank Slangen went on: “Another unique feature was that the entire structure was first rolled over onto the H-541 barge operated by Heerema Marine Contractors, on platform trail-ers, and subsequently onto the Boa Barge 35. Measuring 31.5 metres wide, this transport and installation barge was of precisely the right width to allow the legs and suction piles with reinforcement frames to be suspended down both sides. This work involved the floating crane Matador 3.”

The load-out operation in Flushing.

Sail-away of the fully-assembled

platform on the Boa Barge 35.