Construction work on large-scale subsea Porthos carbon storage with EU backing finally underway


Last fall, the green light finally came, both in a legal and a financial sense. Since then, the Porthos joint venture has, together with five main contractors, been working hard on the final engineering and construction preparations for the carbon transport and underground storage system. The plan is for the first metric tons of CO2 to be pumped into an empty gas field below the North Sea bed in the first half of 2026. The ultimate aim is twofold, namely to achieve the climate targets and to keep major carbon emitters in Europe.

‘What’s new is that we’ll be pumping CO2 and that it will be pumped into a gas field’


Porthos is a project to transport and store CO2 from industrial companies in the port of Rotterdam in empty gas fields below the North Sea bed. Illustration: Porthos

The organisation still has a sense of taking up quarters about it. The outside of the large red-brick multi-user office building in the eastern part of Rotterdam still lacks any kind of sign telling passers-by that this building is also home to Porthos (Port Of Rotterdam Transport Hub and Offshore Storage, but also the name of one of the Three Musketeers). On the fifth floor, they have set up shop in a large room – ‘for now’ – with as many as one hundred workstations, most of which unused when we visited, unimaginatively lined up along the windows. ‘We’re moving to the floor above soon’, says Mark Driessen, who expects to get a more inspiring workplace there. Last fall, he was seconded by his employer, Port of Rotterdam Authority, to work at Porthos, where he became the environment and communication team leader. Also present at the interview is Michiel Goosens, the contract manager seconded by procurement and contract consultancy Aratis. By now, they already have one hundred colleagues, most of whom are planners. With the implementation phase imminent, the workforce is set to grow rapidly over the coming months. Around the time when the project is supposed to be completed, i.e. in mid-2026, most of the staff that will be added will be operational staff.

1.3 billion

The project comprises the development and construction of a large carbon transport and underground storage system, which is generally referred to as ‘CCS’, which stands for carbon capture and storage. In August last year, the Dutch Council of State ruled that the project could go ahead. This ruling came in a case brought by environmental protection organisation MOB, which claimed that the project would generate excessive nitrogen emissions. The Council of State ruled otherwise, clearing the way for Port of Rotterdam Authority, EBN, Gasunie, i.e. the three parties to the Porthos joint venture, to invest in the system. The costs involved in the project total €1.3 billion, which is significantly more than estimated at the start in 2017. According to Goosens, this increase is mainly due to steep inflation and the delays caused by the appeal case. Of this amount of €1.3 billion, €102 million is a grant from Brussels awarded on the back of the project being classed as a Project of Common Interest. The Dutch government also supports the project by offering the companies that will be using the system, i.e. Air Liquide, Air Products, ExxonMobil, and Shell, grants of up to €2 billion if the ETS market price paid for a metric ton of CO2 turns out to be too low to make carbon storage profitable, says Driessen.

New: pumping gas into a gas field

After work on the CCS system initially started as early as in June 2017, the Council of State’s ruling and the joint venture’s investment decision mean that work to finalise the development and actually build the system can now finally go full steam ahead, so that the system will be operational in the first half of 2026. That means storing 2.5 million metric tons of CO2 in gas fields under the North Sea bed at over 3 kilometres from the shore, until these gas fields are filled to capacity with 37 million metric tons after 15 years. To make this happen, what is needed is an onshore pipeline, a cooling water pumping station, a compressor station, an offshore pipeline, and modifications to an existing production platform. ‘This is nothing new in itself’, Driessen explains. ‘Compressing gas and pumping it through pipelines is something we’ve been doing for years. What’s new is that we’ll be pumping CO2 and that it will actually be pumped into a gas field.’

Wait and see

In its original state, the gas field was made up of porous rock with natural gas tucked into its fractions, under about 350 bars of pressure. As gas was extracted from the field, the pressure fell. When CCS is up and running, CO2 will be pumped into the gas field, under a maximum of 310 bars of pressure. ‘What we don’t know exactly at this point’, Driessen explains, ‘is how the gas and the rock will behave. That’s why we’re going to up the pressure gradually, so that we can closely monitor what happens.’

Another issue is that the CO2 comes from four different users who feed in gas with different compositions. ‘How these different kinds of CO2 will behave when mixed is also something we’re going to have to wait and see. After all, a project like this hasn’t been done before anywhere in the world. This is also why we have formulated very tight specifications from a safety and security perspective’, says Driessen. ‘Safety is the top priority in all the specifications submitted to all the main contractors, both during construction and when operating the system after it has been completed’, Goosens adds.

Five main contractors

There are five main contractors – in this case the companies that were awarded the contracts after the European Procurement Procedure that Porthos organised. Italian contractor Bonatti will build the compressor station at the Tweede Maasvlakte industrial park. Dutch contractor Van Der Ven will take care of building the cooling water pumping station at 500 metres from the compressor station. It will be built shoreside because seawater will be used as the cooling water. Belgian contractor DeNys will be laying the onshore pipeline along a distance of over 30km from Pernis right across the busy port of Rotterdam. Allseas was picked to lay the offshore pipeline to the gas field at 21 kilometres from the coast. Finally, German contractor LMR Drilling will do the drilling below the hard seawall of the Maasvlakte industrial park where the pipeline will transition from an onshore into an offshore pipeline.

Different contract types

Contract manager Driessen points out that different types of contracts are used for the five main contractors. ‘With Van Der Ven, we’ve signed a type of construction contract that is commonly used in the Netherlands, based on the Dutch Uniform Administrative Conditions for the Execution of Works (UAV 2012). Porthos designed the cooling water system itself and Van Der Ven has been hired to build it exactly to our specifications. This is a very traditional way of working.’

The agreements with Bonatti for the compressor station were made based on the Fédération Internationale des Ingénieurs-Conseils’ (FIDIC) international Yellow Book standard. ‘For this contract, we only defined the functional specifications and made part of the design. We are leaving it to this contractor to further work out the design. Bonatti has designed and built compressor stations for the oil and gas industry before, so we want to harness their knowledge as much as possible.’ The design will ultimately be implemented in close consultation with Porthos, says Goosens.

Given that the works of Bonatti and Van Der Ven will basically be combined into one large system, with the Italian part compressing the gas and the Dutch part taking care of cooling the compression process, both parties have also signed a ‘coordination agreement’ with Porthos under which they agree to coordinate their activities. ‘There are weekly coordination meetings to make sure that both parts will dovetail perfectly.’

Little space

DeNys, too, has been awarded a design-build contract, in the form of an UAV Integrated Contract that is commonly used in the Netherlands. The challenges for the Belgian contractor are considerable. To an outsider, the port of Rotterdam may seem vast and spacious, but insiders know that it is extremely busy and packed, both above and below ground. There are already a great many pipelines in the area, and work has also started on a large hydrogen pipeline as part of the Dutch national hydrogen network. Driessen: ‘Those pipelines have all been laid in a trench that offers just enough room to hold our one-diameter pipeline as well. Space is also tight when it comes to the actual work of laying the pipeline. This is why we’ve opted for a modular system.’ That means that 20-metre-long pipeline sections will be manufactured in a factory and not in situ. ‘This will enable better quality control and speed up the laying process, with fewer workers and material on site, with less nuisance for local residents, and with safer working conditions for workers.’

The contracts signed with Allseas and LMR are also standardised ones, namely a LOGIC contract (Leading Oil and Gas Industry Competitiveness) and an HbR Design & Construct contract respectively.


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International supply base

The job that Allseas has been given is the one that, on paper, is the least time-consuming. Rumour has it that this Delft-based pipeline laying specialist will be able to lay the 21km offshore pipeline within a time span of around four months. Whether or not the final milestone will be hit in the spring of 2026 will, therefore, depend mainly on other factors and parties, the two men realise.

The contracts entered into with the contractors are watertight when it comes to the obligation to adhere to the schedule, meaning that delivering on time is primarily their responsibility. ‘Mind you, we do see it as a shared responsibility to stay on schedule’, Goosens explains: ‘This is a schedule-driven project. Delays can always occur, but handing out penalties is not what we’re in this for. Porthos wants to do the work together with the contractors based on balanced risk distribution.’

In order to stay ahead of sourcing issues that could cause delays, critical parts were ordered even before construction of the CCS system was given the green light, with the Dutch government as the guarantor. The customer-specific compressor and transformer stations were ordered by Porthos itself from German manufacturer MAN and Portugal’s EFACEC respectively. For all other parts, the contractors can draw on their own supply base. ‘On the condition that they only procure from reputable, established parties, says Goosens.

Preventing the de-industrialisation of Europe

‘While the port of Rotterdam has long ceased to be the world’s largest port, it is the world’s most service-driven port. The CCS system that Porthos is building further adds to the port’s range of services’, according to Driessen. And it also helps tackle current societal issues. On the one hand because carbon storage obviously contributes directly towards achieving the climate targets, and on the other because it can help prevent the de-industrialisation of Europe. Due to the relatively tight climate targets and high energy and CO2 prices in Europe, energy-intensive companies are considering/threatening to move elsewhere. There is plenty of need. The German Ruhr area alone is home to companies that emit an estimated 40 to 50 million metric tons of CO2 every year. However, the 2.5 million metric tons of CO2 per year from the four customers will already fill Porthos to capacity. And so a second mega-project has already appeared on the horizon: Aramis, named after another of the Three Musketeers. A CCS project in the port of Amsterdam named after the third musketeer, Althos, was previously put on hold when Tata Steel in IJmuiden decided to switch to hydrogen.



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