Storing gas under the North Sea is not without dangers

2023-09-05 19:08:31

CO₂storage under the North Sea bed is safe, experts say. However, there are numerous risks to take into account.

Hans Nauta5 september 202321:08

The Rotterdam industry can use CO₂ will be stored under the North Sea bed. The Porthos project has been allowed to proceed by the court, and the final decision to invest is expected within two months. From 2026, 2.5 megatons of CO must be released annually₂, from Rotterdam industry, are stopped three kilometers under the North Sea. This should help slow down global warming. Because a greenhouse gas deep underground is not in the air.

Will that work? Projects that generate CO. worldwide₂ capture and storage do not always do what they promise. Things can go well, like in Norway, and things can go wrong. In Australia it was not possible for several years to reduce CO₂storage at the Gorgon gas extraction project, a joint venture of the oil companies ExxonMobil, Shell and Chevron. The first five years will reduce CO by half₂ saved than promised.

In Algeria, BP was involved in the In Salah project. From 2004 to 2011 there is CO₂ stored in an empty gas field. The project was scrapped due to concerns about a possible leak, which could allow the greenhouse gas to escape.

A greenhouse gas disaster in the US

In California in the US, a major leak actually occurred at a gas storage facility. In 2015, a huge amount of natural gas escaped Aliso Canyon over 111 days. This event is being called the largest man-made greenhouse gas disaster in US history. This wasn’t about CCS, that is carbon capture and storage the capture and storage of CO₂. But it did involve the storage of a gas deep underground, in a former oil field, and the technology is comparable.

The Southern California Gas Company’s gas storage facility where there was a major natural gas leak in 2015/2016.Image EPA

“With any CCS project there will always be a risk of such disasters,” writes gas expert Bruce Robertson of the Institute for Energy Economics and Financial Analysis (IEEFA) in a report with these examples. Pre-set goals are often not achieved, he says about the technology. “Is CCS a solution to our climate problems? I would say no,” Robertson said. It’s much easier to get something out of the ground than to put it in, warns IEEFA.

The oil industry used CO₂ to extract more oil

Injecting CO₂ underground started a long time ago in the oil industry. Adding the gas made it easier to pump the oil. This is still being done. CO₂ therefore started from an economic interest. The climate problem has now been added. The Dutch government wants to use CO₂-storage to reduce emissions in the industry.

Robertson believes that it is better to invest the money in climate solutions that work anyway, such as electric driving and solar and wind energy. Other critics, such as Greenpeace, fear that this technology will keep the world tied to fossil fuels for longer. Oil refineries can continue to operate thanks to CO₂storage, and so we continue to produce and burn gasoline and diesel.

Porthos, a project of the Port of Rotterdam Authority and Gasunie, among others, has four customers, namely the refineries of Shell and ExxonMobil and two hydrogen producers. This project turns gray hydrogen, made from fossil raw materials, into blue hydrogen, with low CO₂-footprint.

Every project in the world is different

Can it be done safely? TNO says yes. This knowledge organization helps companies with the technology required to capture and store CO₂. “CO₂storage is safely possible in empty gas fields under the North Sea. This way, oil and gas installations get a second life there.” the organization says on the website. That doesn’t mean there are no risks.

“Every CCS project in the world is different and has its own technical challenges,” says René Peters, gas expert at TNO. Porthos uses the gas field of Taqa, a company from Abu Dhabi, twenty kilometers off the coast. TNO was involved in research into this gas field when the plan was to use CO₂ to be captured at a Rotterdam coal-fired power station. That plan was canceled. But the knowledge gained is still there.

De CO₂ can leak via two routes

De CO₂ must be stored for centuries. What is the risk that the storage will leak? “There are two ways in which a gas storage facility can leak,” says Peters. “This can be done through the soil via the rock or via the well. Above the gas field that Porthos uses there is a closing clay layer where there is no natural gas and no CO₂ can go through. A leak through the ground is very unlikely.”

A greater risk is a leak along the well through which the gas was extracted and through which the CO₂ is injected, says Peters. “The drilled hole through that clay layer is the only possible escape route for the gas. A steel pipe will be placed in that well, three kilometers deep, and cement will be placed around it. It is important that the cement layer seals well. No problems were discovered during inspections.”

A new steel pipe must be placed in the well. Peters: “Stainless steel, because with CO₂ corrosion is a risk. That is why the gas must be supplied as dry as possible. If water comes with the gas, the pipe can rust.” Rust was one of the causes of the methane leak in Californiain combination with human errors, such as inadequate controls.

The pressure should not be too high

Storing gas is slightly different from pumping gas. “When you start injecting, the pressure in the storage is low, because the gas field is virtually empty. As the field slowly fills up, the pressure increases, and that means you have to inject at a higher pressure. CO₂ it will behave differently as a gas under high pressure, it will resemble a liquid. It’s a special stuff, CO₂. That makes the project challenging. Technically we can arrange that. But it requires extra attention,” says Peters.

There is a limit to how much CO₂ you can save. The pressure in the reservoir may never be greater than before gas extraction started, the environmental impact assessment states. This is in the interest of safe, permanent storage.

A very small chance of an earthquake

Because the pressure changes anyway due to the storage, there is a very small chance of an earthquake. “If an earthquake does occur, it will remain below scale level 4 on the Richter scale. Such an earthquake at sea will barely be felt on the coast and will not cause a tidal wave. The calculated risk of an earthquake is comparable to the extent to which this applies to many gas extraction operations in the North Sea,” the report says.

Also when closing the well after 15 years of CO₂-storage, high pressure plays a role. Peters: “With Porthos you do not place that sealing plug on an empty field, but on a field under pressure.” In the US, a century ago, natural gas wells were sometimes closed by hammering a tree trunk into the pipe and then pouring sand over it, Peters says. Now it is mandatory to close the well by pouring cement into it. At Porthos this is a thirty meter thick layer.

Afterwards, the storage must be monitored for quite some time. The State Supervision of Mines controls this monitoring. Once the pit and platform have been removed, control is no longer possible. If the CO₂ is unexpectedly leaked in the long term, that is a matter for the government. The taxpayer then pays the costs, not the companies that benefit from their CO₂ want to give up.

A suffocating cloud

Porthos’ environmental impact assessment (EIA) describes a number of risks that mainly relate to leaks. Leaking CO₂ can linger like a low hanging cloud. “CO₂ is heavier than air, so it does not simply disappear into the air. It tends to remain around the leak point like a suffocating blanket,” says Peters. The possible causes of a leak are diverse, in theory ranging from an earthquake, corrosion, to sudden failure of a part in the CCS chain, they reported More.

In the port area, the planned pipeline passes through the town of Rozenburg, 125 meters away. This village is located somewhat lower than the immediate area and residents were concerned that the CO₂ would collect in that bowl. The management at Rozenburg therefore receives extra valves in case of an emergency. The Safety Region must prepare for a CO₂-calamity. In extreme cases, evacuation of an area is a possibility. The pipeline must be continuously monitored to know where weak spots arise.

Protect the pipeline from shipping

On the Maasvlakte, a compressor pressurizes the gas and it goes through a pipeline to the former gas field. In theory, leaks can occur along that entire route, from company to storage, says Peters. “For example, a pipeline can be damaged by a ship if the anchor pulls the pipe away. To prevent this, the pipelines are buried in the seabed. Suppose the CO₂ should leak offshore, this can be detected fairly quickly thanks to the gas bubbles that rise to the surface. Then you can reduce the pressure in the system and stop the leak.”

Even if the pressure suddenly drops, CO₂ behave strangely. “CO₂ can then move on to another phase. Then the gas suddenly becomes a solid, and you have a block of CO₂ in your pipeline. How do you solve that again? The strongly cooled CO₂ heats up again and then returns to gaseous form. It is also possible to heat a pipe electrically. But you have to proceed cautiously if you want to shut down the system.”

Sabotage of the Nord Stream gas pipelines between Russia and Germany in September 2022. Large quantities of natural gas emerge.Image AFP

Hackers and terrorists

Many gas platforms in the North Sea are controlled remotely via a fiber optic cable. Cybersecurity is therefore also a theme – you don’t want hackers to take control. “There could also be an attack on a pipeline,” says Peters. “Never say never. Nord Stream (the maritime gas pipeline between Russia and Germany, ed.) has also exploded. Although I don’t see a country planning an attack on a CO anytime soon₂-tube.”

The same safety measures apply to Porthos as in the oil and gas industry to prevent leakage or other possible problems. Peters: “Every project has risks. Porthos has slightly different technical challenges than the projects in Algeria, America or Australia. But because the risks have been identified, we can minimize them as much as possible.”

Also read:

Industry likes CO₂ store under the North Sea

A windfall for Dutch industry. Companies such as Shell and ExxonMobil can still use CO₂ store under the North Sea. The Council of State has allowed the Porthos project to continue.

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