Once a symbol of fossil fuel extraction, the remote Nini oil field in the North Sea is preparing for a new role: storing millions of tonnes of carbon dioxide beneath the ocean floor.

Chemical giant INEOS, through its Greensand Future project, is preparing to launch what will become the European Union’s first fully-operational offshore carbon dioxide storage site. The project will begin commercial operations in 2025, marking a major step forward for Europe’s climate strategy.

In essence, the process flips traditional oil extraction on its head by injecting liquefied CO2 back into the same reservoirs that once supplied crude oil.

“We are able to create an industry where we can support Europe in actually storing a lot of the CO2 here,” said Mads Gade, CEO of INEOS Energy Europe. He believes Denmark could ultimately store more than “several hundred years of our own emissions.”

Turning old wells into climate infrastructure

Greensand is based around the Siri platform, just off the Danish coast, where depleted oil reservoirs lie nearly 1,800 meters beneath the seabed. The rock formations below, specifically Greensand sandstone, are porous enough to hold the injected gas, according to geologists.

“We found that there (are) no reactions between the reservoir and the injected CO2,” explained Niels Schovsbo of the Geological Survey of Denmark and Greenland. He added that the rock above has enough strength to seal in the pressure created underground, making the site “a perfect location for storage.”

Initial operations will focus on burying around 363,000 metric tonnes of CO2 per year, with ambitions to scale up to 7.3 million metric tonnes annually by 2030.

To support this effort, a new CO2 terminal is under construction at the Port of Esbjerg, and a purpose-built vessel named Carbon Destroyer 1 is being built in the Netherlands to transport the liquefied gas.

Why carbon capture is part of the climate solution

Carbon capture and storage (CCS) is gaining traction globally as a way to reduce emissions from industries that are otherwise difficult to decarbonize. Proponents argue it is an essential part of the toolkit for reaching net-zero targets, especially when paired with renewable energy and deep efficiency.

The Intergovernmental Panel on Climate Change (IPCC) has recognized CCS as a necessary technology in scenarios that limit global warming to 1.5 degrees Celsius.

“We don’t want to deindustrialize Europe,” said Gade. “We want to have actually a few instruments to decarbonize instead.”

The European Union has proposed scaling up to 227 million tonnes of CO2 storage per year by 2040. Projects like Greensand could serve as early proof points for meeting that goal.

Why critics say storage isn’t a substitute for cuts

Despite its promise, CCS remains controversial. Critics say it shouldn’t become a crutch for industries reluctant to reduce emissions at the source.

“We could have CCS on those very few sectors where emissions are truly difficult or impossible to abate,” said Helene Hagel, head of climate and environmental policy at Greenpeace Denmark. “But when you have all sectors in society almost saying, we need to just catch the emissions and store them instead of reducing emissions—that is the problem.”

The scale is another challenge. While Greensand aims to bury 7.3 million tonnes of CO2 annually by 2030, global emissions exceeded 34.5 billion tonnes last year, according to the International Energy Agency.

There’s also scrutiny over the project’s parent company. While INEOS leads Europe’s largest carbon storage initiative, it is also pursuing development of a new oil field in the North Sea. Gade defended the move, saying, “The footprint we deliver from importing energy against producing domestic or regional oil and gas is a lot more important for the transition.”

“We see a purpose in doing this for a period while we create a transition for Europe,” he added.

Storage is a start, but not the finish line

The Greensand project is a technological milestone and a potential model for turning fossil fuel infrastructure into climate assets. But whether carbon storage becomes a cornerstone or a detour in climate policy will depend on how it’s deployed and how committed governments and companies remain to cutting emissions at the source.

For now, Europe’s first full-scale offshore CCS site represents a real, physical shift: from taking carbon out of the ground to putting it back in and keeping it there.