At that time, contract negotiations had been pursued with Norwegian Contractors on building a four-shaft Condeep gravity base structure (GBS). They were at the point where a letter of intent was ready.
The recently established Norwegian Petroleum Consultants (NPC) joint venture had also signed a contract on project management and engineering design for Statfjord B. Read more about NPC in the section on Statfjord B – the first plan.
While the contract for building the platform topside and mechanical outfitting of the GBS shafts had yet to be awarded, an option agreement had been secured with the Aker group.
So all the main contracts for the project appeared to have been put in place. The Storting (parliament) had also approved phase II of the development plan in June 1976, and most people assumed that it was simply a case of starting to build.
Until the NPD letter arrived
The Vogt commission
New safety regulations for the Norwegian offshore industry had been adopted on 9 July that year. A key issue for Statfjord B and the field licensees was the introduction of a more restrictive attitude towards simultaneous drilling and production combined with living quarters on a single integrated platform.
The new rules had been developed by a commission of inquiry appointed by the government as early as 22 May 1970 with a mandate to propose regulations for the safety of production and storage facilities on the seabed and of exploiting petroleum deposits.[REMOVE]Fotnote: Norsk Oljerevy. (1976). no 2. Kontroll med sikkerheten fordelt på ni instanser.
Work in the commission progressed slowly and its chair, Jens Evensen, asked to be relieved. He was replaced in November 1972 by director general Lars Oftedal Broch, who was replaced in his turn during May 1974 by Nils Vogt from the NPD.
The latter gave his name to the commission’s report, which was submitted to the Ministry of Industry on 12 July 1975. It was then circulated for consultation to affected companies and institutions.[REMOVE]Fotnote: Hanisch, T., Nerheim, G., & Norsk petroleumsforening. (1992). Fra vantro til overmot? (Vol. 1). Oslo: Leseselskapet: 324.
Adopted by royal decree of 9 July 1976, the new safety regulations were based on the recommendations of the Vogt commission and on comments received in the consultation process. One provision of the decree was that the NPD would bear primary responsibility for supervising fixed offshore installations.
Safety issues on Statfjord were viewed by the directorate through the prism of the new regulations. It kept the industry ministry informed about its work, and wrote the following in a letter dated 7 July 1976:
“Given the work being done on safety conditions, it has been found necessary to adopt a more restrictive attitude to those concepts which are based on combined drilling and production, where the living quarters are also placed on the same platform. The main intentions of the Vogt commission’s recommendations run counter to both combined activity and the above-mentioned placement of living quarters … The NPD would emphasise that combined drilling and production will only be accepted following individual analyses and assessments. The same applies to living quarters which it is proposed to place on a drilling/production platform. No final choice of concept has been made for Statfjord B, so no specific safety analysis has been submitted. Comments from the NPD will accordingly have to wait until it the actual conditions have been presented.”[REMOVE]Fotnote: Norsk Oljerevy.
In other words, the ministry had been informed of the NPD’s work and of its scepticism about the plans for Statfjord B. As the letter indicated, the regulator could not adopt a final position until the Statfjord Unit Operating Committee (SUOC) had approved the concept chosen for the B platform in late August 1976. Only then could the NPD conduct its own safety analysis.
The results of the latter were presented to the Statfjord licensees in the above-mentioned letter of 11 November 1976, where the NPD questioned the safety of an integrated platform and ordered the construction of a separate quarters platform:
“The NPD is currently assessing the concept for Statfjord B on the basis of a general evaluation of the safety rules on the field in the light of the new regulations (royal decree of 9.7.76)
“Statfjord B is expected to involve:
- particularly complex and extensive production facilities concentrated on a single platform
- a large number of producing wells with high capacity, along with water and gas injection
- permanent living quarters for 200 occupants, which will be used by 400 people during the construction phase and possibly the drilling phase
- possible simultaneous drilling and production.
“The total risk is characterised by the contributions from each of the activities and processes which include the examples given above. The NPD’s assessment is that the total risk associated with these conditions lies at too high a level.
“In the NPD’s view, the best way to reduce the total risk would be to reduce the number of people who are present on the platform at any given time. The NPD has accordingly concluded that a separate quarters platform connected to Statfjord B should be built.”
This safety assessment was not confined to Statfjord B. Questions were also posed about the A platform, construction of which was far advanced at the time. It was due to be towed out to the field in six months.
“The considerations mentioned above also apply to Statfjord A, if to a somewhat lesser degree. The NPD would accordingly, on the basis of the provisions in the royal decree of 9.7.76, request that the company undertakes a new overall assessment of safety conditions [on this installation] in relation to the planned drilling and production programme, with particular attention paid to the accommodation issue.”
This letter was signed by Gunnar Hellesen, chair of the NPD board, and director general Fredrik Hagemann.
New concepts proposed
Statfjord B was intended to be a virtual copy of the A platform, but with four support shafts instead of three. The process facilities would be equally large and complex, with a production capacity of 300 000 barrels per day, and the 200-berth quarters module was to be installed on the platform.
It was the last feature in particular that the NPD wished to prevent. The regulator took the view that cutting the number of people on the platform at any given time would reduce the overall risk.
As the letter indicates, the desirable solution was seen to be the construction of two platforms – one for production and drilling, and the other for accommodation. The NPD also emphasised the need for overall safety thinking, and wanted a separate safety study carried out before detailed planning began.
Statoil and Mobil expressed surprise at the letter, and claimed they had not heard that such assessments were being made. Arve Johnsen, then Statoil’s chief executive, described his reaction to the letter in his book Utfordringen (The Challenge): “As chief executive of Statoil, I received many kinds of letters … I have forgotten most of them, but I will remember one to my dying day … It sent a shock wave through the licensees in the Statfjord group.”[REMOVE]Fotnote: Johnsen, A. (1988). Utfordringen : Statoil-år. Oslo: Gyldendal: 202.
It might seem incomprehensible that the partners had failed to see this coming. They had long been aware that the NPD was looking at problems associated with simultaneous drilling and production, and the Vogt commission’s report had been through a consultation process. Comments in the latter as well as the report itself formed the basis for the new safety regulations.
Adopted in June, four months before the letter was despatched, the regulations specified that simultaneous drilling and production was prohibited without special permission. This should have sent certain signals that the plans for Statfjord B might be more difficult to implement than Mobil and Statoil thought.
As late as 12 October, section head Harald Ynnesdal had explained the NPD’s view on the issue in a speech he gave in Kristiansand:
“The new platform types are particularly complex and difficult to assess from a safety perspective with regard to these combined activities. As far as possible, fields should be planned with separate quarters platforms. The production platforms could then, with their combined activities, be assessed purely as industrial plants.
“In an assessment of simultaneous drilling and production in the Statfjord project, for example, the problem would have been much simpler if separate quarters platforms had been adopted. The cost of such platforms would have had little effect on profitability for this project, but would have meant a great deal for overall safety and the desire for an early start to production.”[REMOVE]Fotnote: Norsk Oljerevy. (1976). no 9. Statfjord – planer og virkelighet. On the basis of this letter, an extraordinary meeting of the SUOC was called on 26 November. It decided that all activities related to Statfjord B would be halted. The project would have to be re-evaluated, and extensive conceptual studies were to be carried out for every option from one to three platforms.
A meeting of the Statfjord field engineering committee (SFEC) – the technical project team – took place in January 1977. A 35-strong sub-committee was appointed to study and assess various conceptual solutions for Statfjord B, and came up with 39 variants for consideration.
When the SUOC met again on 18 March, Statoil expressed concern at the progress made. The project had a tight timetable, and order books at the Norwegian shipyards were empty. To speed up the process, the company proposed a separate drilling platform linked by a bridge to a combined production and quarters unit.
A drilling platform supported on a steel jacket, for instance, would be relatively cheap to build and could be ready for tow-out as early as 1979. Drilling of production wells could start as soon as the platform was in place, and continue while the associated production and quarters facility was under construction.
As soon as the latter had been installed, oil and gas could thereby begin.[REMOVE]Fotnote: Norsk Oljerevy. (1977). no 5. Industrien må fortsatt vente på Statfjord B. This meant in turn that the original schedule set in the field development plan could be met.
Mobil and Saga were strongly opposed to this plan, but did not have enough votes to block it. Their interests added up to only 25 per cent, while resolutions in the SUOC needed 70 per cent support. The Statoil proposal was thereby adopted – against the operator’s vote.
Esso also proposed its own solution at the meeting, comprising an integrated production, drilling and quarters (PDQ) platform but with processing capacity halved to 150 000 barrels per day. This facility would be simpler, since only one process train was required rather than the original two, and overall safety would be improved.
Mobil supported the Esso proposal. The two companies were uncompromising in their opposition to two platforms, and maintained that this would provide no safety benefit. A factor in their assessment was the poor seabed soil conditions on Statfjord, which meant that installing two platforms so close to each other and linked by a bridge carrying high-pressure pipelines would pose a safety risk.
The thought of the substantial capital investment required for two platforms also worried the operator. On the other hand, experience from other North Sea projects suggested that a capacity of 150 000 barrels per day would be sufficient. Such a solution would reduce construction costs by simplifying the platform, and production could also start earlier.
A further meeting of the SUOC was held on 28 April, when Mobil proposed an integrated platform with a single process train and an average capacity of 180 000 barrels per producing day. This size had been chosen in the hope of avoiding a separate quarters platform.
The change to the original concept was so large that a completely new field development plan might have to be produced. According to the proposals approved the Storting in the summer of 1976, three platforms with a combined capacity of 900 000 barrels per day were to be installed.
Reducing the size of the process facilities on each platform would either require more structures to maintain the planned output, or a slower pace of production.[REMOVE]Fotnote: Norsk Oljerevy. (1977). no 5. Industrien må fortsatt vente på Statfjord B. Fresh consideration by the Storting could delay the project further.
At the same time, Mobil vetoed a separate quarters platform.[REMOVE]Fotnote: Moe, J. (1980). Kostnadsanalysen norsk kontinentalsokkel : Rapport fra styringsgruppen oppnevnt ved kongelig resolusjon av 16. mars 1979 : Rapporten avgitt til Olje- og energidepartementet 29. april 1980 : 2 : Utbyggingsprosjektene på norsk sokkel (Vol. 2). Oslo: [Olje- og energidepartementet]. With strong support from Esso, the operator noted that it could not accept a solution which complied with the NPD’s principle that drilling and production should not take place simultaneously on the same installation.
Clear instructions had been sent from Mobil’s head office in New York that a compromise solution which would involve an acceptance of the NPD principle was out of the question. It feared that conceding this demand from the Norwegian regulator could lead to similar requirements on other continental shelves, which would have major consequences for both Mobil and its fellow oil companies.
A telex from New York emphasised that, the way things looked, concrete platforms on the scale of Statfjord A had outplayed their role on this field. Mobil was willing to renounce the operatorship for Statfjord B if a two-platform solution was adopted. This attitude took Statoil and the Norwegian government by surprise.[REMOVE]Fotnote: Norsk Oljerevy. (1977). no 5. Industrien må fortsatt vente på Statfjord B.
Statoil explored the possibility of another operator, but none of the other partners was willing to take on the role without a reallocation of licence interests. Mobil and Esso had staked their prestige on the issue, and they finally managed to convince Statoil of the technical problems posed by a two-platform solution. The argument that this could affect later developments in deeper water was central to the Norwegian company’s change of mind.
The discussion on one or more platforms and the studies of various concepts were paralleled with the presentation of new seismic data for the field. These cut its estimated oil reserves from 3.9 billion barrels – equivalent to 527 million tonnes – to 3.2 billion or 432 million tonnes. That reduced the need for two process trains on Statfjord B.
On 5 August, the SUOC approved plans for a platform with the capacity to process 180 000 barrels per day. It was resolved on 29 November to apply to the NPD for permission to build such a structure. The application, accompanied by a separate safety study, was submitted on 1 December.
Plans now called for Statfjord B to be installed in 149 metres of water at the southern end of the field. Seabed conditions were poorer there than over the rest of Statfjord, and the base area of the GBS accordingly had to be increased.
While Statfjord A had 19 cells, the B version would have 24. Planned topside space would expand correspondingly, from 5 200 square metres to 7 800. The platform would still have four shafts even though only one process train was to be installed. With the fourth shaft reserved for risers, space was freed up in the others.
Additional safety barriers were introduced by the decision to make the decks and modules open, reducing the danger of an explosion and possible damage from such an incident. The various functions would also be positioned in such a way that no hazardous operations were close to or beneath the living quarters. And the quarters modules would be protected by an additional fire wall. These plans were approved by the NPD on 19 December.
The project had been delayed by a year and incurred substantial costs through a number of conceptual studies and reports. According to Henrik Ager-Hanssen, deputy chief executive of Statoil, the letter from the NPD was the most expensive in Norwegian history and cost the project NOK 25 million per word.
Viewed from a different perspective, former Statoil staffer Bjørn Vidar Lerøen has noted that oil prices reached record levels over the next few years. That meant the letter became one of Norway’s most profitable.[REMOVE]Fotnote: Lerøen, B., Gooderham, R., & Statoil. (2002). Drops of black gold : Statoil 1972-2002. Stavanger: Statoil: 149.
More about statfjord b
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The GBS accordingly represented the biggest challenge yet faced by Condeep builder Norwegian Contractors (NC). It surpassed all previous platform projects in both size and complexity.
Standing 174 metres high, the completed structure contained 135 000 cubic metres of concrete and roughly 35 500 tonnes of reinforcement bars (rebars). Its base section was 169 metres long and 143 metres wide, covering an area of just over 1.8 hectares – or three football pitches.
Its 24 cells could store about 1.8 million barrels of oil, and 98 steel and concrete skirts were installed under its base..[REMOVE]
Fotnote: Steen, &., & Norwegian Contractors. (1993). På dypt vann : Norwegian Contractors 1973-1993. Oslo: [Norwegian Contractors]: 44.
By comparison, Statfjord A and all the other previous Condeeps had 19 cells and three shafts. They had a base area of 8 000 square metres, 89 000 cubic metres of concrete and 17 240 tonnes of rebars.
An important part of the GBS’s function was to transport itself and the topside out to the field. And big benefits were obtained by completing as much as possible of the support structure, topside and outfitting in sheltered inshore waters, before towing the platform out and sinking it on the field without any preparation of the seabed.
One design parameter for the GBS was the ability to support a topside tow-out weight of 35 000 tonnes. The corresponding figure for Statfjord A had been 20 000 tonnes. So the Statfjord B GBS had to be substantially increased in size to cope with the extra weight. Its buoyancy needed to be high, with a corresponding large volume of ballast where the moment between buoyancy and ballast was small.[REMOVE]Fotnote: Dahl, Per C. og Olsen, Olav. (1978, 20. oktober). Statfjord B – interessant konstruksjon med mange nye trekk. Norsk Oljerevy Ba 4, nr. 7/8.
As mentioned above, the base area was increased from about 8 000 square metres on the earlier Condeeps to no less than 18 000 square metres in order to ensure sufficient buoyancy. Cell storage was increased from 1.2 million tonnes on Statfjord A.
Another reason for such a big expansion in the base area was that seabed conditions at Statfjord B’s intended location were significantly poorer than for the A platform. Several innovations were developed to alleviate this problem.
First, the GBS was provided with a “cellar” section, an enclosed space under the cells and above the base plate. In addition to helping overcome the bottom conditions, this solution had several advantages.
It provided space for piping systems which had been cast inside the concrete on earlier Condeeps, for instance. Since the cellar was dry until the cells had been cast, pipework could be installed during that period.
The external pipelines – risers – to and from the platform had been installed outside the cell walls on earlier Condeeps, which called for extensive diving work to weld pipes together on the seabed. But the cellar on Statfjord B provided space to conduct the risers through pipes directly to the fourth shaft, where they could be welded in the dry once this “riser” shaft had been emptied of water.[REMOVE]
Fotnote: Dahl, Per C. og Olsen, Olav. (1978, 20. oktober). Statfjord B – interessant konstruksjon med mange nye trekk. Norsk Oljerevy Ba 4, nr. 7/8.
Installed beneath the cellar/base plate, the 98 steel and concrete skirts also had several functions. Plans called for the platform to be installed directly on the unprepared seabed. As in many other areas, the upper layers of the sea bottom were less consolidated than those lower down.
So rigid steel skirts were important, because they would cut down into the soil to reach a depth which could bear the load. They also protected against the seabed being washed out, and served as a framework for concrete grouting beneath the platform.
Pressure in the skirts was also kept below the ambient level. Combining overpressure and underpressure in the spaces between the various skirts, the platform could be manoeuvred more surely during its installation.
Thanks to the skirts, too, the structure could also be safely placed on sloping ground. Maintaining overpressure in the relevant skirts kept the platform level until grouting had been completed.[REMOVE]
Fotnote: Dahl, Per C. og Olsen, Olav. (1978, 20. oktober). Statfjord B – interessant konstruksjon med mange nye trekk. Norsk Oljerevy Ba 4, nr. 7/8.
Yet another innovation on Statfjord B was the increase in the number of shafts from three to four. Experience with Statfjord A and other earlier concrete platforms showed that a four-shaft layout was more appropriate for supporting the topside. Although the Statfjord B GBS was built in the same way as its predecessors at Hinnavågen outside Stavanger, it incorporated so many changes that it ranked as a new Condeep generation.
A dedicated organisation comprising NC’s own personnel was needed to manage and control such a giant project. Both Mobil as the client and NC also hired external expertise, with Mobil awarding a consultancy contract to EMC – a joint venture between Brown & Root and Norway’s NPC.
For its part, NC hired Grøner og Noteby to support the construction management team and to conduct quality control of its own work. It also hired the Olav Olsen A/S consultancy to do construction engineering, prepare drawings and make calculations for the concrete work, the Norwegian Geological Institute (NGI) for foundations and instrumentation, and Det Norske Veritas (DNV) for technical calculations.
The Norwegian Petroleum Directorate (NPD), which was responsible for seeing that work complied with official safety regulations, hired Dr Ing Aas Jacobsen to check drawings, calculations and the execution of concrete and steel construction. This consultancy had done the same job on Statfjord A.
With DNV checking the mechanical systems, drawings were accordingly assessed by three different bodies – Aas Jacobsen for the NPD, DNV for NC and EMC for Mobil. The level of change orders for building the Statfjord B GBS was low.[REMOVE]
Fotnote: Moe, J. (1980). Kostnadsanalysen norsk kontinentalsokkel : Rapport fra styringsgruppen oppnevnt ved kongelig resolusjon av 16. mars 1979 : Rapporten avgitt til Olje- og energidepartementet 29. april 1980 : 2 : Utbyggingsprosjektene på norsk sokkel (Vol. 2). Oslo: [Olje- og energidepartementet]: 231.
NC began the job of readying the construction site before Mobil had awarded it the contract to build the Statfjord B GBS. The first step was to move a pipeline used to pump out seawater which seeped under the sheet pile retaining wall. This extended too far into the dock.
A larger foundation was also required. It had previously covered some 0.8 hectares, but the planned dimensions of Statfjord B meant this had to be expanded to two hectares. After an investigation, it was decided that the existing foundation could be incorporated in the new one.[REMOVE]Fotnote: Stavanger Aftenblad. (1978, 24. januar). Klar for B-plattformen.
Once the contract had been formally signed, work on improving the ground began before the new foundation was cast. The dock had to be drained and part of the spoil had to be removed. A good base for the concrete foundation was important – it had to cope with a weight of 110 000 tonnes which was unevenly distributed.
The bottom section of the GBS was towed out of the dry dock on 11 June 1979 and moored in the Gands Fjord off Stavanger while preparations were made to slipform the cells. This tow-out was a critical phase. The section had to be pulled out of the inner dock for 100 metres, before being turned 23 degrees and then towed out of the opening.
Very little wind could be tolerated, and the job had to be postponed twice. The first attempt was aborted after it transpired that bottom conditions at the dock gate had not been properly prepared, so that the draft was too shallow. A 70 000-cubic-metre support bank had to be removed. Excessive wind prevented the second try.
But everything went according to plan the third time, and the bottom section was pulled out of the dock by winches with just 70 centimetres of clearance over the bottom.[REMOVE]Fotnote: Stavanger Aftenblad. (1979, 28. juni).
Once the structure was clear of the dock, the winch cables were severed and the tugs took over. Compressed air, buoyancy and 20 000 horsepower divided between five tugs made it possible to move Statfjord B to the mooring site at a speed of two-three knots.
Attaching and tightening the moorings took two days.[REMOVE]Fotnote: Rogalands Avis. (1979, 11. juni). Condeep-utslep med forviklinger.
The chains intended to hold the structure in place were fixed to new attachment points. Four lengths measuring a total of six-seven kilometres were used.
The chains were of better quality than those used before, since the GBS would be significantly larger. With a breaking strength of 1 500 tonnes, compared with 1 300 tonnes before, they were attached to Lihalsen and Einerneset on the eastern shore of the Gands Fjord, and Vaulen and Kvalaberg on the western side. The attachments were simpler in design than their predecessors. No winches were placed on land, only steel plates set into the bedrock.[REMOVE]Fotnote: Stavanger Aftenblad. (1979, 5. januar). Svær kjetting til Statfjord b.
Slipforming of the cells started at the same time as the school summer holidays. This was important in order to recruit students and thereby obtain sufficient labour. The job was well paid, and it was not difficult to get workers. People had to be turned away. Most of the holiday personnel pushed wheelbarrows, but NC also held courses for them in iron fixing and formwork construction.
This was the most hectic period, with 1 150 people at work. NC’s own personnel accounted for 860 of these. The slipforming continued around the clock for 27 days, making it the world’s biggest operation of its kind until then. A total of 58 000 cubic metres of concrete were poured from wheelbarrows. Each of the latter held 80 litres and, to achieve the desired slipforming speed of 1.5 metres per second, one wheelbarrow had to be filled every three seconds.[REMOVE]Fotnote: Steen, &., & Norwegian Contractors. (1993). På dypt vann : Norwegian Contractors 1973-1993. Oslo: [Norwegian Contractors]: 44.
The work was heavy and a high pace was maintained. Workers were divided into four shifts. After six hours of pushing wheelbarrows or binding rebars, the body ached and fingers were stiff. Concrete was mixed in a plant on a barge moored alongside the GBS.
A dozen temporary office buildings for administrators were also installed out in the fjord. Personnel were ferried to and from the GBS by high-speed craft.[REMOVE]Fotnote: VG. (1979, 12. juni). Betong-gigant PÅ FJORDTUR.
Slipforming the cells was carefully planned, with no margin for error. Hundreds of hydraulic jacks controlled by laser beams thrust the formwork upwards. The job was completed by 18 July, and a temporary halt was called to permit completion of the cells and make preparations for slipforming the shafts. That operation began the following January, and the top was reached on 24 February. The GBS was now no less than 174 metres high. Despite the tight schedule, work was finished a day early.
NC now had to reduce its workforce again, from 650 people to about 350. The 150 employees recruited for slipforming the shaft moved on to other jobs, while many of the remaining 150 returned to jobs with the partners in NC – Furuholmen, Høyer-Ellefsen and Selmer. NC found work for the rest elsewhere, including at Rosenberg Verft. The latter was in the middle of building the Statfjord B topside.[REMOVE]
Fotnote: Rogalands Avis. (1980, 11. mars). På toppen av Statfjord B.
Work on the Statfjord B GBS proceeded largely without dramatic incidents, but one accident did occur in December 1979. This involved a silo containing 50 tonnes of fine-crushed iron ore, a small barge and a loading shovel worth several hundred thousand kroner, which sank in the Gands Fjord. Nobody was injured.
The mishap occurred during discharging of fines (iron ore crushed into small-grained particles) representing half the 40 000 tonnes due to be used as ballast in the GBS base. Two cranes on the ore carrier were transferring this cargo to two silos standing on separate pontoon moored to the platform. Conveyor belts ran from the silos to the GBS.
Without informing the crane driver, the belt from one silo was halted to check some hoses. The driver thought ore was still flowing out of the silo and continued loading even when the latter was full. Thanks to the overload, the pontoon concerned developed a list, the legs supporting the silo broke and the container fell onto a barge moored alongside and carrying a loading shovel. Silo, iron fines, barge and shovel vanished in 243 metres of water and a thick layer of bottom mud.[REMOVE]
Fotnote: Stavanger Aftenblad. (1979, 21. desember). Shovel og silo gikk til bunns.