Finn Harald Sandberg, Norwegian Petroleum Museum
Stavanger’s Rosenberg Verft yard won the job of assembling the Draugen topsides in early 1990. This massive jigsaw formed an integrated structure, with components and equipment packages put together at the construction site.
— The construction of Draugen topside takes place at the Aker Rosenberg Shipyard at Buøy in Stavanger. Photo: A/S Norske Shell/Norwegian Petroleum Museum
The topsides were originally intended for a floating production platform, which meant they were much lighter than a traditional complex used on a fixed installation.
That in turn proved appropriate for a concrete gravity base structure (GBS) with a single support shaft, since it would keep stability during towout within safety requirements.
The topsides were 79 metres long, 59 metres wide and 15 metres high (figure 1). Their quarters section was almost 23 metres tall and contained 130 berths.
During earlier projects, the Rosenberg yard – part of the Moss Rosenberg Verft (MRV) company – had used four specially built concrete cylinders to support the topsides structure.[REMOVE]Fotnote: Statfjord industrial heritage – Building the Statfjord B topside
Standing in the water alongside the dock, these pillars were intended to imitate the shafts of the GBS which the topsides would rest on – as with the Statfjord and Gullfaks structures.
However, the Draugen platform only had one shaft. In addition, the top of this monotower was larger than earlier points of contact and virtually square.
That presented a challenge which had to be overcome before assembly work could begin. The answer proposed was a kind of both-one-thing-and-another solution.
To accommodate barges to float the completed topsides to nearby Vats for mating with the GBS, two of the four concrete cylinders had to be placed at the seaward edge of the structure.
These stood immediately beneath the quarters section, and were supplemented by smaller concrete blocks supported by steel tubes and positioned on the seabed to imitate the top of the monotower.
Similar blocks were also spaced along the edge of the support frame to distribute the topside weight and thereby avoid damage. They could easily be removed to let the barges in (figure 2).
The detail engineering job for the Draugen topsides had been awarded in 1989 to Kværner Engineering. Like MRV, this company was a member of the Kværner fabrication group.
Covering the drawings used in tendering for and building the topsides, this contract was signed by project director Mahdi Hasan for Shell and senior executive Hans Jørgen Frank for Kværner.[REMOVE]Fotnote: Interview with project director Mahdi Hasan, 11 August 2018.
This pair also put their names to the construction and outfitting assignment for the topsides when it was awarded to MRV in early 1990.
Since both design and construction were to be carried out by companies in the same family, the prospects for a positive outcome looked promising.
Computers at the engineering and fabrication firms talked the same language, allowing them to communicate. With such intimate collaboration, the job should have presented no problems.
Nevertheless, this proved yet another offshore development where the design drawings were less than perfect – as had been the case in several projects off Norway during the 1980s.
The latter had experienced major cost overruns, in part because of variation orders (VOs) during the construction phase. On Draugen, the flow of these amendments seemed endless.
The yard faced problems dealing with all the changes to the drawings, with disruptions and discontinuities affecting assembly. Both time and costs became difficult to control.[REMOVE]Fotnote: Nerheim, Gunnar, Jøssang, Lars Gaule and Utne, Bjørn Saxe (1995). I vekst og forandring – Rosenberg Verft 100 år: 442-443.
In fact, awarding these two contracts to companies in the same group may have contributed to the disagreements which arose during the construction period.[REMOVE]Fotnote: Interview with Sigbjørn Ellingsen, production vice president, Rosenberg Verft, 19 January 2017.
The topside was originally costed at NOK 1.1 billion, but the bill had almost doubled to NOK 2.1 billion when Shell took delivery at the towout in February 1993.[REMOVE]Fotnote:Stavanger Aftenblad, 13 January 1996, “Pinlig for Shell, verst for Kværner”.
MRV’s contract was a pure construction job. This meant that all proposals for variations from the design drawing – from minor improvements to major conversions – had to be approved by Shell.
The Rosenberg yard accordingly sent such suggestions to the client, who then had to pass them to the engineering company for redrafting.
However, Shell’s project team took the view that these proposals should go directly to Kværner Engineering and be sorted out between the two group companies.
That approach would have been similar to the one used in the integrated engineering, procurement and construction (EPC) assignments which had become common in Norway’s offshore sector.
This was precisely what Shell had envisaged and hoped would happen when it awarded both contracts to two companies in the same group.
These two different interpretations of the contractual relationship meant that VOs piled up without being dealt with, and work at the yard was delayed by the absence of a response.
Although this bottleneck was eventually resolved, a lot of critical time had been lost and it became important to speed up the remaining work.
But disagreement over the contract persisted, and the final bill had to be settled by arbitration. This process dragged out, and took three years to bring to an end on 11 January 1996.[REMOVE]Fotnote:Stavanger Aftenblad, 13 January 1996, “Pinlig for Shell, verst for Kværner”.
On behalf of the licensees, Shell had originally claimed NOK 1.47 billion from Kværner. This was later reduced to NOK 576 million.[REMOVE]Fotnote:Aftenposten, 13 January 1996, “Draugenseier til Kværner”.
Shell based this demand on allegations of intentional or grossly negligent material breaches of the contract by Kværner, but these were dismissed by the arbitration tribunal.
Kværner secured extra compensation of NOK 113 million because Shell had demanded an acceleration of the work, which meant the yard had to take on more personnel than originally planned.[REMOVE]Fotnote:Dagens Næringsliv, 13 January 1996, “Shell tapte mot Kværner”.
Although the hearing ended in victory for Kværner, local daily Stavanger Aftenblad still headlined a comment by journalist Arnt Even Bøe: “Embarrassing for Shell, worst for Kværner”.
He wrote that this case and others still to be resolved meant that the group had earned itself a reputation as the company which took legal action against its customers.[REMOVE]Fotnote: Stavanger Aftenblad, 13 January 1996, “Pinlig for Shell, verst for Kværner”.
 Statfjord industrial heritage – Building the Statfjord B topside
 Interview with project director Mahdi Hasan, 11 August 2018.
 Nerheim, Gunnar, Jøssang, Lars Gaule and Utne, Bjørn Saxe (1995). I vekst og forandring – Rosenberg Verft 100 år: 442-443.
 Interview with Sigbjørn Ellingsen, production vice president, Rosenberg Verft, 19 January 2017.
Stavanger Aftenblad, 13 January 1996, “Pinlig for Shell, verst for Kværner”.
Stavanger Aftenblad, 13 January 1996, “Pinlig for Shell, verst for Kværner”.
Aftenposten, 13 January 1996, “Draugenseier til Kværner”.
Dagens Næringsliv, 13 January 1996, “Shell tapte mot Kværner”.
 Stavanger Aftenblad, 13 January 1996, “Pinlig for Shell, verst for Kværner”.
Published October 29, 2018 • Updated December 19, 2018
After four years of wrangling, the outcome was that A/S Norske Shell had to pay a total of NOK 311 million on behalf of the field’s licensees.[REMOVE]Fotnote: NTB, 12 January 1996, “Shell tapte voldgiftssak om Draugen-dekket”.
NOK 2.1 billion had already been paid following delivery of the structure from the Kværner yard in February 1993, but the two sides could not agree on the final amount.
They had continued to negotiate on a number of issues related to this settlement, and managed to resolve most of the matters in contention.
However, stalemate was reached in the autumn of 1994. Claims and counterclaims were presented, and one of the biggest arbitration hearings in Norwegian legal history began that August.
Kværner had originally claimed NOK 200 million in compensation for forcing the pace of fabrication work – a demand later reduced to NOK 165 million.
For its part, Shell maintained that the yard had breached the contract either deliberately or through gross negligence, and presented a compensation claim of NOK 1.47 billion.
This was later restricted to NOK 576 million on condition that the Draugen licensees were allowed to retain a bank guarantee of NOK 198 million.[REMOVE]Fotnote:Dagens Næringsliv, 13 January 1996, “Shell tapte mot Kværner”.
The final adjudication rejected Shell’s claim, thereby handing Kværner a complete victory. Shell had to pay NOK 113 million for the bank guarantee and as a supplement for extra work. In addition came interest and legal fees.
According to communications vice president Atle Kigen at Kværner, this settlement was worth NOK 225 million to the group in 1995-96.[REMOVE]Fotnote:Aftenposten, 13 January 1996, “Draugenseier til Kværner”.
Published October 24, 2018 • Updated November 13, 2018
The operator decided to drop the detailed design requirements which had been usual since the early 1980s, and opted instead for the recommendations made by Norway’s Norsok project.
Intended to enhance the competitiveness of the Norwegian continental shelf, the latter had come out in favour of performance-based specifications for offshore facilities.
Setting clear demands for user functionality, safety and the working environment, without going into details, would offer cheaper, more efficient and safer solutions.[REMOVE]Fotnote:Nytt fra A/S Norske Shell, summer 1992, “Nytt borekonsept for internasjonalt marked”.
Norske Shell required that analyses were conducted with the work operations and crew most vulnerable to accidents, and how such incidents could be avoided.[REMOVE]Fotnote:Nytt fra A/S Norske Shell, summer 1992, “Sikkerhet og arbeidsmiljø i sentrum”.
The attention devoted to safety and performance-based requirements gave the newly formed Hitec-Dreco joint venture the opportunity to turn its innovative ideas into reality.
These in turn would create a new generation of drilling rigs for fixed offshore installations worldwide.
One member of this partnership, established in 1989, was Hitec, a Stavanger-based specialist in instrumentation, electrical engineering and computer systems.
The other was Canada’s Dreco, which delivered all types of drilling equipment to the global market. This company also had experience of tough climatic conditions from delivering modularised rigs for Arctic exploration.
John McGill was in many respects the pivotal figure in this new constellation, and served as Hitec-Dreco’s chief executive during the first few years.
After leaving a Norwegian drilling company in 1987, he had many ideas about how equipment could be improved in terms of safety and the working environment. And these proposals would not least involve big reductions in both weight and price.
A plethora of new ideas was put forward when the joint venture got started. Not all of these were equally good – most were actually rejected.
But a good climate of cooperation between the two teams yielded very interesting concepts. When the invitation to tender for Draugen arrived, a creative forum could come up with viable options.
The drilling module was not to have a long life on the platform. It was removed in 1997 and subsequently had an interesting career. Read more about where the rig ended up.
Published October 19, 2018 • Updated October 19, 2018
Finn Harald Sandberg, Norwegian Petroleum Museum
Norwegian blocks first became available above the 62nd parallel (the northern limit of the North Sea) with the fifth licensing round in 1979. And acreage was finally awarded across the whole Norwegian continental shelf (NCS) – from the North to the Barents Seas – during the eighth round in 1984.
— This field lies in block 6407/9 in the Norwegian Sea, where a production licence was awarded on 9 March 1984 as part of the eighth licensing round. Photo: Shadé Barka Martins/Norwegian Petroleum Museum
A/S Norske Shell secured interests in two eighth-round production licences (PLs), including PL 087 in block 16/4 where Norsk Hydro was operator. Two dry wildcats have been drilled there.[REMOVE]Fotnote: Oljedirektoratet: Faktahefte 1987
A/S Norske Shell secured interests in two eighth-round production licences (PLs), including PL 087 in block 16/4 where Norsk Hydro was operator. Two dry wildcats have been drilled there. However, Shell was named operator for PL 093 – which today encompasses the Draugen field – with Statoil and BP as its partners.
This licence proved an immediate success. Its award was announced on 9 March, the first wildcat was already under way on 26 June, and the well had been completed by 7 September.
Clear indications were found of a good-quality and substantial reservoir containing primarily oil. Making a discovery within six months of the licence award was unusual.
Shell also managed to maintain a rapid pace in developing the find. The plan for development and operation (PDO) was approved in 1989, less than five years after the discovery. Moreover, Draugen came on stream within a decade of being found – about five years faster than other NCS fields in the same order of size and during the same period.
A total of 17 blocks were awarded in 1984, with PLs numbered from 86 to 100. Five were in the North Sea, five in the Norwegian Sea between Trondheim and Brønnøysund (including Draugen) and five in the Barents Sea.
The eighth licensing round has proved one of the most successful set of awards made on the NCS with regard to the number of commercial discoveries.
At the time, North Sea block 34/7 attracted the greatest expectations. This acreage was covered by PL 89, which has proved to contain various reservoirs developed under different names. Snorre produces through two platforms, while little Sygna is a subsea field tied back to Statfjord along with the Statfjord East satellite. In addition come two further subsea developments – Tordis and Vigdis. These have been tied back to Gullfaks C and Snorre A respectively.
Licences awarded in addition to PL 34/7 in the eighth round have otherwise resulted in the following field developments:
Heidrun (Norwegian Sea), on stream October 1995
Åsgard (Norwegian Sea), on stream May 1999
Fram (North Sea), on stream October 2003
Mikkel (Norwegian Sea), on stream August 2003
Snøhvit (Barents Sea), on stream August 2007
Tyrihans (Norwegian Sea), on stream July 2009.
In addition, the Peik discovery is under consideration for development in 2018 – more than 30 years after the block was licensed. Four of the licences are considered non-commercial.
Blocks awarded during the eighth round contain recoverable reserves of nearly 11 billion barrels of oil equivalent (1.75 billion standard cubic metres).[REMOVE]Fotnote: Oljedirektoratet. (2018) Faktasider – Felt – Reserver Hentet fra http://factpages.npd.no/factpages/Default.aspx?culture=no Lastet ned 27.04.2018 That corresponds to almost a fifth of all the oil and gas discovered on the NCS.
Published August 24, 2018 • Updated October 17, 2018
The operator planned to place orders worth some NOK 35 billion (equivalent to roughly NOK 65 billion in 2018 money) for these two projects. Draugen accounted for almost a third of this amount.[REMOVE]Fotnote: Dagens Næringsliv. (1989. 27. januar). Shell-kontrakter til 35 milliarder kroner.
That proportion reflects the fact that Shell’s Troll A plans covered the world’s largest offshore gas field, and included a massive concrete gravity base structure (GBS) for the platform.
Plus the topsides, this whole facility would stand 472 metres high at tow-out in 1995. That makes it the world’s tallest structure moved by humans.
Less than six months after Troll A came on stream, Statoil took over as production operator for the gas development in accordance with the terms of the licence agreement.
The award of the NOK 500 million detail design contract for the Draugen topsides to Norway’s Kværner Engineering (KE) was announced on 15 March 1989.
About 450 people would be employed in designing this steel structure, including outfitting, living quarters and drilling facilities.
KE was also responsible for planning the test programme and commissioning for the platform once it was in position on the Halten Bank area off mid-Norway.
Shell was also very keen to ensure competition over building the GBS, a business where Norwegian Contractors (NC) had become a virtual monopoly supplier with its Condeep solution.
The operator worried that this would mean a higher price than if several companies competed for the work, and accordingly invited the Peconor group to submit a tender.
This contractor had done a good job in building the protective barrier for the Ekofisk tank in the North Sea, and Shell thereby felt it could be a viable competitor to NC.[REMOVE]Fotnote: Donoclift, P. (Phillips Petroleum Co. Norway), Gijzel, T.G. (Peconor Ekofisk/VSO), Hjelde, H.G. (Peconor Ekofisk/AVECO) &VeldkampJ.R. (Peconor Ekofisk/VSO. (1990). Transport and Installation of Protective Barrier Ekofisk 2/4 Tank. Paper presentert på OTC-6472–MS.
Norske Shell nevertheless announced on 31 August 1989 that the NOK 1.7 billion contract had gone to NC. Gregers Kure, CEO of the latter, expressed himself “incredibly pleased”.
This job would form an important basis for the GBS specialist’s future activity and for the development of new concepts.
During the period before the Draugen award, NC had been forced to reduce its workforce from 1 500 people to around 700. Now its staffing and technical expertise could be preserved.[REMOVE]Fotnote: NTB. (1989. 31. August). Norwegian Contractors vant konkurransen om Draugen-plattformen.
The three Norwegian fabricators invited to bid for building the 18 000-tonne topsides for the Draugen platform were announced on 28 July.
With no foreign companies included in the list, the deadline for tenders was set to mid-November with the contract award scheduled for early 1990.
The licence terms committed Shell to involve mid-Norwegian industry as much as possible, and the invitation to tender stated that the successful fabricator must inform possible sub-contractors in that part of Norway of its needs at an early stage in the process.[REMOVE]Fotnote: NTB. (1989. 28. juli). Ren norsk konkurranse om bygging av Draugen-dekket.
It emerged on 26 January 1990 that the Kværner Rosenberg yard in Stavanger had landed the NOK 1.1 billion assignment, which was that year’s largest offshore job for Norway’s fabricators.
Tore Nordtun, mayor of Stavanger, declared that this was “a fantastic day for Rosenberg, for the region and for local industry in the town”.[REMOVE]Fotnote: Stavanger Aftenblad. (1990. 26. januar). Rosenberg bygger Draugen-dekket.
Seven months later, it became clear that KE would secure the NOK 150 million contract for engineering services related to following up fabrication of the topsides.
Provision was made for close collaboration between the two Kværner companies, with KE responsible for delivering drawings, materials and equipment to the construction job.[REMOVE]Fotnote: Dagens Næringsliv. (1990. 28. august). Ny kontrakt til Kværner.
In addition to the major GBS and topsides contracts, Shell placed a number of important orders for the procurement of important platform components.
Kværner’s contract for the main power generators was among the very first of these to be clarified in August 1989. Worth NOK 220 million, this job called for the equipment to be supplied to Stavanger in early 1991.[REMOVE]Fotnote: NTB. (1989. 28. juni). Kværner leverer generatorer til Draugen-plattformen.
The following major and more minor contracts were placed during the autumn and winter:
25 August 1989. Deck cranes to Stålprodukter A/S in Molde. Value NOK 30 million.
31 August 1989. Pressure vessels to Orkdal Offshore/Orkla Engineering. Value NOK 1.5 million.
1 November 1989. Equipment for process control and safety systems to EB Industri og Offshore. Value NOK 50 million.
4 December. Lifeboats to Harding Safety A/S at Ølve in Hardanger. Value NOK 25-30 million.
6 December 1989. Construction and outfitting of the quarters module to Hitec-Dreco in Stavanger. Value NOK 165 million.
13 January 1990. Fire doors to Rapp Bomek A/S in Bodø. Value NOK 150-200 million.
23 February 1990. Freight and forwarding in connection with the development to Vestbase in Kristiansund. Value NOK 50 million.
29 March 1990. Actuator-controlled valves to ScanArmatur in Stavanger. Value NOK 20 million.
31 May1990. Telecommunications equipment to EB Industri og Offshore. Value just over NOK 47 million.
In addition to equipment for installation on the platform, the Draugen development also covered separate subsea installations to help recover oil from the field.
The contract for this delivery went to Kongsberg Offshore. Announced on 2 June 1990, it was worth NOK 480 million.[REMOVE]Fotnote: NTB. (1990. 2. juli). Draugen-kontrakt til Kongsberg.
Draugen would also be the first field in the world to feature a special subsea pumping system known as a Shell multiphase underwater booster station (Smubs).
This was intended to pump an unprocessed mix of oil, gas and water (as well as accompanying sand) from the seabed production wells to the platform six kilometres away.The contract with Kongsberg Offshore specified that the equipment should be ready for testing at the company in good time before installation on the field.
Actual fabrication of Smubs had a price tag of just under NOK 16 million, but the equipment was the outcome of a three-year research project which had cost NOK 30 million.At the end of this 18-month procurement drive, Norske Shell had thereby placed contracts worth more than NOK 4.5 billion for the Draugen development.
Published August 24, 2018 • Updated October 4, 2018
Finn Harald Sandberg, Norwegian Petroleum Museum
The Draugen platform comprises a round concrete monotower and an almost square steel topside. Putting drilling and oil transport functions in a single shaft posed a range of safety challenges. Moving from circular to square cross-section also proved testing.
— Top of the shaft with gliding formwork. Photo: Eivind Wolff/Norwegian Petroleum Museum
A technique known as “gliding formwork” or “slipforming” was used to construct the vertical sections of the concrete gravity base structures (GBSs) built in Stavanger and elsewhere. This was a special form of a “climbing formwork”, where a form is constructed and then disassembled once casting has been completed. It can then be reinstalled to cast the next section. That approach is preferred when constructing vertical sections of limited height, such as in residential properties or foundations.
Such cases involve a limited number of disassembly/reassembly operations. The method is advantageous where many cutouts – such as windows – are involved. Slipforming was the best approach for the big concrete GBSs because it permitted continuous construction with few joints and cost-efficient working.
Figure 2 shows how this is typically built up. The actual formwork comprises a vertical sheet installed to ensure that wall thickness and shape meet the design specifications.
Gangways are installed on both sides of the wall around the whole circumference to provide a work space and access for such jobs as installing reinforcement bars (rebars) and cutouts. Other tasks here include pouring concrete into the forms, applying epoxy, inspecting the finished result and repairing possible surface blemishes.
Formwork and gangways are attached to frames hung from hydraulic jacks, which move up as the structure rises. If the design requires changes in diameter, the formwork radius can be adjusted with a horizontal jacking system.
As concrete is cast, the whole formwork get raised by activating the jacks simultaneously. Adjusted to the curing time of the concrete, the speed of the glide will vary with complexity and volume and is normally 1.5 to four metres per day.
The jacks are constantly adjusted to adapt the formwork to the desired shape of the concrete wall and to correct possible variations without exceeding tolerances specified in the chosen building standard.
Careful control of shaft geometry is exercised with the aid of laser measurements to ensure that all dimensions meet the tolerances throughout.
The conical shaft in the Draugen GBS has its narrowest diameter at the sea surface, where it measures just over 15 metres compared with more than 22 metres down at the storage cells.
That reduces wave forces acting on the platform and thereby allows its base section to be reduced, as well as securing a more efficient design.
However, a circular cross-section with a relatively small diameter was not the optimal solution for the transition to the square topside.
The top of the shaft was accordingly designed as a box structure with a square cross-section measuring 22 metres to a side.
Designing and operating a slipforming process where the cross-section gradually changed from circle to square therefore presented a challenge in construction terms.
This required both a variation in wall thickness and an increase in external dimensions – squaring the circle in practice.[REMOVE]Fotnote: Tegning GS D 2001-001 GENERAL VIEW
The solution involved a system which made it possible to add additional formwork sheets as the slipformed area increased, and creating a frame with arms which stuck out from the centre.
A horizontal jacking system controlled the distance from the centre to the formwork, and this approach provided a successful outcome.
The formwork could be raised so that the shaft wall became a double arc with its external dimensions tailored to a favourable solution for designing and attaching the topsides.
One result of this building technique was that a checked pattern emerged on the transition piece, which gives the Draugen platform a characteristic appearance.
Based on an e-mail from Dag N Jensen, former head of engineering design at Norwegian Contractors.
To start with, the platform ranked at the time as the tallest structure ever towed. It was also the first fixed installation to be positioned above the 62nd parallel – making the tow-out the longest to date on the Norwegian continental shelf (NCS).
The Condeep monotower was readied in March 1993 to receive the topsides, which were to be towed from Stavanger to the deepwater mating site at Vats.
On 24 March, the concrete structure underwent a trial submersion which left only a few metres of the shaft visible above the sea surface.
This operation was a nervous time, with the Sleipner sinking (see separate article) the year before still fresh in the minds of most people present. But everything went as planned.
In the meantime, the topsides were being completed at Stavanger’s Rosenberg Verft yard. On 6 March, this structure was transferred to two huge barges and towed to Vats by five tugs.
Mating was accomplished by manoeuvring the barges into position over the concrete shaft and deballasting the gravity base structure (GBS).
Tolerances were narrow. The maximum permitted deviation from an ideal match of topsides and shaft was a mere 40 millimetres – so accuracy was essential in all stages of the operation.
As large volumes of water were pumped from its storage cells, the GBS rose, took over the weight from the barges and continued to raise the topsides high above the sea surface.
The mating operation was completed entirely to plan, and all that remained before the platform could begin its journey north was to hook up piping and cable systems.
In beautiful weather, the tow-out began on 3 May. Six big tugs with a combined 75 000 horsepower in bollard pull were needed to cover the 830 kilometres to the field.
As mentioned above, this was the longest-ever tow for a Condeep platform. Completing the voyage without risk depended more than ever on a long period of fine weather.
The operation took 10 days at an average speed on 1.5 knots. It crossed the 62nd parallel – the northern boundary of the North Sea – at 04.58 on 11 May, and reached its destination on 13 May.
The platform was finally in position on 17 May, Norway’s Constitution Day, and an improvised parade was staged on the helideck.
Installation on the field
Some concern was expressed when the tow began in early May because an error in casting the GBS had created a problem for ballasting the platform down on the field.[REMOVE]Fotnote: Interview with Eivind Wolff, Norwegian Contractors project director, 20 October 2016.
Extensive seabed surveys and geotechnical sampling had been conducted on Draugen as early as 1992. These revealed that the platform site comprised very soft clay over a harder layer.
As a result, the platform was equipped with nine-metre long skirts to ensure good penetration. However, their thick walls would displace much of the unconsolidated seabed material.
This soft clay would be squeezed into all the spaces beneath the storage cells, including the three-cornered gaps formed when three cylinders are placed next to each other (see figure 1).
Unfortunately, an inspection had revealed that these supposed three-cornered spaces were not empty but had been filled with concrete.
This meant the seabed material had nowhere to go when the skirts penetrated. That could cause a soil collapse, damaging the whole platform foundation and perhaps leaving it unusable.
The casting error and poorer bottom conditions than expected meant that the tolerance for positioning the GBS had to be narrowed from a diameter of 20 metres to just eight metres.
Sigbjørn Egeland, Shell’s construction supervisor for the GBS, sums up what happened as follows:
When the platform had bee placed just two metres from the ‘bull’s eye’, the job of ballasting down began to ensure adequate skirt penetration in the seabed. This would normally have been a relatively straightforward process – simply pumping water out of the storage cells so that external water pressure would drive the structure into the seabed. The skirts had almost reached full penetration when we were informed that only half of them were in contact with the hard layer. The soft clay overburden was thicker than expected and the hard layer sloped slightly. This sparked an extensive and hectic series of meetings to find a solution to the unexpected discovery. To achieve a solid ‘landing’ and ensure a good grip on the hard clay by the remaining parts of the skirts, the platform had to be positioned ‘slightly askew’.[REMOVE]Fotnote: E-mail from Sigbjørn Egeland, Shell’s construction supervisor for the concrete GBS, 14 February 2017.
This proved very challenging. The solution adopted was to adjust the internal underpressure in the cells. But that created pressure differentials on different sides of the platform.
The was process very extensive and difficult. Nobody had done anything like it in practice before, and calculating the amount of pressure differential was complicated.
Things had to done calmly and carefully, and took at least a week longer than a normal installation. The result was that the platform had a tilt of about 0.3 degrees (“I think the exact figure was 0.296 degrees,” says Egeland).
That might not seem like much, but on a structure more than 300 metres tall it adds up to a horizontal offset of about 1.5 metres. The lifts and the derrick had to be adjusted accordingly.
Those who complained most were the pool players – all the balls accumulated in one corner.[REMOVE]Fotnote: Interview with Bjarne Jensen, Shell’s survey representative for installation of the Draugen platform, 11 October 2016.
Finn Harald Sandberg Norwegian Petroleum Museum
When Norway became an oil nation in the late 1960s, few people expected Norwegian construction companies to be among the biggest suppliers to the forthcoming North Sea developments.
— The construction is just starting in the dry dock in Jåttåvågen near Stavanger, where Draugen will be built. Representatives from the construction client start by releasing the first concrete from the concrete bucket. Photo: Norwegian Contractors/Norwegian Petroleum Museum
The formation of Norwegian Contractors (NC) in 1973 as a joint venture between A/S Høyer-Ellefsen, Ingeniør F Selmer A/S and Ingeniør Thor Furuholmen A/S nevertheless demonstrated that the country had its own resources for meeting the big new challenges.
This became particularly clear through a unique creation – the concrete deepwater structure (Condeep) to support production facilities on the continental shelf.
These gravity base structures (GBSs), which sit solidly on the seabed through their own weight, introduced prestressed concrete as a construction material for the offshore sector.
They combined a number of technical advantages with a short construction time and low lifetime costs, and thereby represented big savings for the oil companies.
NC’s development can be split into three phases, starting in 1973 with the contract to build the first Condeep for Mobil’s Beryl A platform in the UK North Sea sector.
The initial five years were a typical pioneering period, where attention was concentrated on delivery and less concern was paid to further development.
This period ended with the delivery of the GBSs for Statfjord A and the TCP-2 platform to stand on the Frigg field in the course of 1977.
The next phase covered 1978-88 and embraced the construction of six Condeeps – all for licences operated by Norwegian companies.
It was now the government demanded that it must be possible to remove concrete platforms from the fields when production had ceased. All Condeeps had to be designed accordingly from 1980.
The final phase began in 1988 with the start to constructing the first Sleipner A GBS and ended with the delivery of the Troll A platform in 1995.
NC made a big leap forward technologically during this period by introducing several new platform solutions simultaneously, both fixed and floating.
Water depths down to 300 metres represented a particular challenge, and the Draugen GBS marked an important product in this context.
The Sleipner A GBS sank in the Gands Fjord in April 1991 (see separate article). This had consequences for the whole of NC and posed challenges for the Draugen, Troll and Heidrun platforms.
Many people contributed to the development of the Condeep concept. Three who were particularly important in this context are mentioned here.
Engineer Olav Mo came up with the idea for the structure, and played a big role in its technical refinement. He later applied for a patent covering the design.
Helge Molland was the executive responsible for developing collaboration with other companies and for the active market cultivation required to succeed with such a pioneering project.
His enthusiasm and ability to put the case allowed him to make a big contribution in the demanding initial period.
Dr techn Olav Olsen was Norway’s leading expert on shell structures and involved in the development work from the word go. He produced the final solution used for Beryl A and played a highly significant part in subsequent designs.
Many people earned their first oil money and financed their studies through long summer days on and beside the Gands Fjord, where these concrete gravity base structures (GBSs) were raised by a process known as slipforming. Stout backs and strong arms were required to build these huge structures. One experience is described below.
Some of these workers have also regarded their experience of the platforms and constructing them as the great challenge of their lives.
One of these was Swede Gunnar Gramnes, who wanted to give the Norwegian oil adventure a try during the summer of 1986 and has provided the following account (abridged).
“There were 1 200 of us. We came from Cameroon, Angola, Czechoslovakia, Canada, Poland, West Germany and the UK, and naturally from Finland, Denmark, Norway and Sweden.
“We included experienced old construction workers, who got the jobs they wanted, young people who had fled unemployment at home, university students and a few expectant adventure-seekers.
“There were almost as many different reasons for being there as there were souls. But we all shared two motives – to make money and to participate in the world’s biggest slipforming operation to date.
“I was personally one of the adventure-seekers. That’s how it felt, at least, when I boarded the train at Stockholm’s central station for the 17-hour journey to Stavanger.
“Pouring concrete was my job, and God knows I did enough of it. The old office-worker body suffered a real shock after its first shift – eight hours of continuously pushing a wheelbarrow with 150 kilograms of concrete.
“This went on round and round a scaffold inside cell E4. When the chance came for a break after four hours of intensive work, I ached everywhere and was convinced that the adventure would end after a single shift.
“The mood in cell E4 was high-spirited throughout that summer. I was lucky, and worked only with Norwegians. And I’ll never forget my eight cell comrades.
“A great camaraderie developed between us as we struggled with or against the ever-rising formwork, which climbed remorselessly at its fixed rate of 53 centimetres per shift.
“I managed to complete my 12 regular shifts, and even an extra one, and returned home from Stavanger considerably stronger and with greater self-confidence than ever.
“Whenever I tell curious colleagues about my days on the ‘slip’, I feel a sense of pride – over surviving the big strength test, over the good camaraderie, over learning about other working lives remote from my own.
“And I’m proud of having been involved with the fantastic structure which an oil platform represents.”[REMOVE]Fotnote: Steen, &., & Norwegian Contractors. (1993). På dypt vann : Norwegian Contractors 1973-1993. Oslo: [Norwegian Contractors].
Working on the slip has also inspired poetry of the kind written by Erling Thu and included in his 1976 collection of Condeep Kvardagsdikt (Everyday Condeep Verses). See the Norwegian version of this article for an example.