[Caption: Carbon dioxide (CO2) is separated from the well stream on the Sleipner T platform . (Photo: Dag Myrestrand)
Norway’s oil giant Statoil that merged last year with Norsk Hydro to form StatoilHydro, has been storing every day nearly 2,800 tonnes of carbon dioxide (CO2) that is removed from natural gas produced on its Sleipner West field in the North Sea every day.
The carbon dioxide is injected and stored in the Utsira formation, contains porous sand rock filled with salt water, rather than being emitted into the atmosphere. This sandstone formation extends over a large area in the Norwegian sector of the North Sea. The facility has been online since 1996, recording a very high regularity.
The company believes that carbon storage under the seabed may be an important tool in the efforts to slow global warming.
StatoilHydro says its research and monitoring of the carbon injection into the Utsira formation show that the greenhouse gas is retained in the formation and that this is an environmentally friendly and safe way of reducing climate gas emissions.
“This is a good carbon capture demonstration project. Sleipner documents that carbon storage is feasible and safe,” says Rolf Håkon Holmboe, head of HSE on the Sleipner field.
“We wish to build on the experience we have gained through 12 years of operations employing carbon capture and storage techniques,” says Sjur Talstad, vice president, Sleipner production.
Used for other discoveries?
The Sleipner organisation is exploring the possibilities of offering other petroleum discoveries in the area the opportunity to process gas, remove CO2 from the gas and store it in the Usira formation.It says the possibility of receiving carbon dioxide from land for injection into the Utsira formation is also being considered.
The EU aims to cut Europe’s carbon emissions by 20 per cent by 2020 and carbon storage may be one of several necessary requirements. A decision by the EU Parliament as to whether, and on what conditions, such storage may be permitted is scheduled for 2008.
CO2 capture is done at Sleipner with a conventional amine process. The company says it was a challenge to design this process compact enough so that it could be placed on an offshore platform in the middle of the North Sea, 250 kilometres from land.
The extra equipment cost for the CO2 compression and the drilling of the CO2 injection well was roughly $100 million. Until now eight million tonnes of CO2 have been stored. The spreading of the CO2 underground has been mapped in various research projects, which were partly financed by the European Union (EU).
In 1990 the Statoil-operated gas condensate field Sleipner Vest in the North Sea was in its planning phase. The natural gas at Sleipner contains naturally around 9 per cent CO2, much higher than customer requirements, and had to be removed first.
In 1991 the Norwegian authorities introduced a CO2 offshore tax aimed at reducing CO2 emissions, which currently is around $50 per tonne. Statoil proposed to remove the CO2 offshore and inject it into a deep geological layer below the Sleipner platform, where the seperated CO2 will be stored, probably thousands of years, says StatoilHydro. This layer contains porous sand rock filled with salt water, and is called the Utsira formation. The CO2 is prevented from seeping into the atmosphere by a 800 metre thick gastight cap rock above this layer.
The Sleipner license partners supported this idea as its implementation meant a reduction in CO2 emissions of nearly one million tonnes per year, which was roughly 3 per cent of the Norwegian CO2 emissions in 1990.
The field became operative in October 1996, making it the the world’s first offshore CO2 capture plant, together with the world’s first CO2 storage project in a geological layer 1000 metres below the sea floor.