OSLO (Reuters) - Chemicals group INEOS has taken a final investment decision with partners to build a CO2 storage project off Denmark, potentially the first such EU project to start operations, the firm owned by British billionaire Jim Ratcliffe said on Tuesday. The Greensand Future project aims to initially inject up to 400,000 tonnes a year of CO2 emitted at Denmark's biomethane plants for permanent storage at a depleted oilfield from the end of 2025 or early in 2026, INEOS said.

Greensand Future is the third CO2 project in the North Sea to take a final investment decision, after the $621 million Northern Lights in Norway and the $1.3 billion Porthos project in the Netherlands.

"Greensand Future will be the first CO2 storage facility in operation in the EU supporting both Danish and EU's climate objectives," INEOS Chairman Jim Ratcliffe said in a statement.

Greensand project was initiated by the INEOS-led consortium a few years ago with the Danish government awarding it a 197 million Danish crown grant in 2021. INEOS has declined to disclose the size of the investment in the storage, citing commercial reasons and ongoing negotiations.

Northern Lights in non-EU member Norway is a joint venture between Equinor, Shell and TotalEnergies. It was completed in September and plans to start CO2 injection in 2025.

The Porthos project at Rotterdam's port aims to start injecting CO2 into depleted gas fields on the Dutch continental shelf in 2026.

INEOS' partners in the Danish project are British oil and gas firm Harbour Energy and Nordsoefonden, which manages the Danish state's interests in offshore oil and gas licences.

INEOS said the decision to invest in the storage, opens the way for total investments of more than $150 million in a broader value chain of CO2 liquefaction, transportation and storage.

The sum is lower than other CO2 capture and storage projects in the region as it will reuse the existing wells to inject the CO2 into an underground reservoir, people familiar with the project said.

Biomethane plants already separate CO2 from methane, meaning that CO2 only needs to be liquefied before it can be transported, avoiding the need for expensive capture installations, they added.

INEOS said the storage capacity could be gradually expanded to up to 8 million tonnes by 2030, depending on demand.

($1 = 11.1154 Norwegian crowns)

(Reporting by Nerijus Adomaitis; Editing by Susan Fenton)

By Nerijus Adomaitis