Safety in steel
Photo: Aker / Norwegian Petroleum Museum
Photo: Aker / Norwegian Petroleum Museum
Why were the Ekofisk platforms built with steel jackets, while Statfjord’s facilities rest on concrete gravity base structures (GBSs)? When did subsea developments begin to dominate, and what role have safety regulations played in platform design on the NCS? Read on to find out.
Facilities of many different types, sizes and materials have been installed over the course of 50 years to recover oil and gas from the seabed on the Norwegian continental shelf (NCS).
They have all been constructed to handle demanding drilling, production and processing jobs – and to ensure these activities involve no harm to people, the environment and material assets.
Their designs result from an interaction between industry responses to technological challenges and government requirements for managing risk and shaping offshore workplaces.
The American way
Much of Norway’s existing expertise on structures at the time when its oil adventure began derived from experience with dams, bridges and ships. The emerging Norwegian offshore industry accordingly had to adapt swiftly to solutions which had primarily been utilised in other parts of the world.
The technology required for building offshore facilities which rested on steel jackets was first developed in the Gulf of Mexico after 1945. The first such permanent installation was put in place on the seabed as early as 1946, and more than a thousand of them had been constructed in the Gulf by 1963.
Since water depths at the southern end of Norway’s North Sea sector were fairly similar to those in the Gulf, similar structures were a natural choice there. The first three facilities on Ekofisk were jacket-supported, and platforms of this type could eventually be found on a number of other Norwegian fields in relatively shallow water, such as Valhall, Odin, Frigg and Ula.
Oil and gas operations on the Norwegian continental shelf (NCS) were characterised initially by the award of production licences to large foreign companies and by drilling and service companies hailing largely from the USA.
They already had long experience from American waters, allowing them to develop technical standards and work operations for offshore operations. These US norms were also applied to the NCS. But they had little to say about such aspects as working conditions, for example.
With the passage of the Working Environment Act in 1977, the Norwegian government raised such issues as noise, ergonomics and chemical exposure. That eventually had consequences for designing NCS facilities.
Rough and manual
Working conditions in Norway’s offshore industry were characterised during its first couple of decades by much manual labour involving heavy and hazardous equipment. The American approach to personal safety was often to send people who made mistakes home on the first helicopter. That could also happen if they reported dangerous or unhealthy working conditions. The result was a relatively large number of injuries.
A widespread view within risk research at the time was that cutting the number of personal injuries would also reduce the risk of major accidents. As the personal injuries declined, however, no corresponding decrease was observed in the number of incidents with a major accident potential.
The government and the scientists therefore had to accept that no necessary relationship existed between the risk of personal injury and the underlying threat of major accidents.
From Ekofisk to Condeep
Several big discoveries were made during the 1970s in the deeper waters of the northern North Sea, such as the Statfjord and Troll fields in 150 and 300 metres respectively. Not only did this pose technological challenges for platform structures, but pipeline systems able to export oil and gas to market were also difficult and costly to lay.
Norway’s Condeep platform technology therefore represented a response to the challenges presented by depth and storage requirements. The concrete GBSs supporting these structures offered particular benefits of robustness in relation to weather, waves and currents. In addition, all the topside production facilities could be installed on the GBS before towout. That removed the need for heavy and demanding lifting operations offshore.
Their drawback was high construction costs as well as the difficulty – in practice, virtual impossibility – of removing them after production ceased. As a result, Condeeps on the NCS have been confined to big fields with long production horizons.
The GBS for the first Condeep platform was built for Britain’s Beryl field, and introduced what must be characterised as a Norwegian industrial adventure. No less than 14 of these structures were build in Jåttåvågen outside Stavanger from 1975 to 1995, including three for use on the UK continental shelf.
Condeeps on the NCS have been installed on Frigg, Statfjord, Gullfaks, Oseberg, Draugen, Sleipner and Troll, which all rank as “giants” among Norway’s oil and gas fields.
The concrete letter
Statfjord A was among the first concrete giants approved for the NCS in 1976, when nothing similar to these structures had been built before. The company which designed the A platform topsides on behalf of operator Mobil concentrated primarily on the processes and less on creating a good working environment, logistics and the like.
After a series of modifications, the Norwegian Petroleum Directorate (NPD), which then embraced the PSA, found that the necessary safety standards were met. It came on stream in 1979.
When operator Mobil submitted plans to build Statfjord B as a copy of the A structure, however, the NPD put its foot down and sent the US company what has often been called “Norway’s most expensive letter”. This required the living quarters to be placed on a separate structure. After many meetings and long discussions, however, Mobil won acceptance for a single platform with a modified design.
The solution it and the other licensees ended up with was a longer topsides which offered better opportunities to separate accommodation from those areas with a higher potential for such incidents as fires and explosions. This concept later formed the basis for the Statfjord C facility and the three Condeep platforms installed by operator Statoil on the Gullfaks field.
This approach – incorporating good solutions as early as the planning stage – was later extended to other types of risk. It became more usual, for example, to take account of employee experience when designing workplaces. That has improved the physical working environment and reduced the risk of personal injury. In turn, sickness absence has declined and efficiency increased.
Beneath the waves
Technological advances led to a new shift from the 1980s, when big integrated concrete and steel facilities began to be replaced by subsea solutions tied back to existing installations. Right from the start of Norway’s oil history, discoveries had been made which were not considered commercial on their own. However, this picture changed as an extensive infrastructure of production platforms and pipelines was put in place.
It became clear in the 1980s that developing such marginal fields could be made profitable as well as acceptable in safety terms with the aid of subsea installations. Wellstreams could be piped from templates installed on the seabed to a nearby fixed facility or a floating production unit for separating and exporting the oil and gas.
Several major technological advances made this development possible, including multiphase pipeline flow able to carry a mix of oil, gas, condensate and water over ever longer distances. Specially built remotely operated vehicles (ROVs) capable of performing complex jobs on subsea Xmas trees and other seabed equipment were also introduced at this time.
In 1992 the NPD introduced regulations which called for remote handling of all tubulars less than 20 inches in diameter on the drill floor and in transit from the pipe racks. The aim was to get people off the drill floor – a dangerous place to be, with many accidents including serious injury and death.
Although specific demands for mechanical pipe handling have not been incorporated in the regulations of other countries, this technology also dominates the international scene. That is not only because safety improves, but also because experience shows that it reduces downtime and thereby makes drilling more efficient.
Our time and onwards
A lot of facilities are still being constructed for the NCS. The world’s largest Spar platform was installed last year on Aasta Hansteen in the Norwegian Sea, for example. Best described as resting on a big vertical steel cylinder, this installation is tailored for deep water and demanding offshore conditions.
The floating platform is 339 metres high and weighs 70 000 tonnes. It sits in no less than 1 300 metres of water – making it the deepest NCS development to date. Seventeen polyester cables, each 2.5 kilometres long, hold the structure in place.
At the same time, the Oseberg west flank 2 project marks a move in a different direction – one which required detailed regulatory processes before approval was given in June 2016.
The plan for development and operation (PDO) included a completely unmanned wellhead platform remotely operated from the Oseberg field centre, which came on stream in October 2018.
This Oseberg H facility only has people on board for one or two annual maintenance visits. It thereby provides no quarters, helideck or lifeboats – not even a toilet. Personnel will go on board from a vessel fitted with a walkway.
Text: Thor Gunnar Dahle og Stian Danielsen