Every year since 1996, we have captured one million tonnes of carbon dioxide from natural gas production at Sleipner West and stored it in an aquifer more than 800 metres below the seabed. On Sleipner, carbon dioxide is captured using a conventional amine process and stored in geological layers.

During the planning stage, it was a challenge to make the processing equipment compact enough for there to be space for it on a platform out in the middle of the North Sea, 250 kilometres from land.

The extra costs in connection with the compression and injection of carbon dioxide amounted to about USD 100 million.

At the beginning of 2011 almost 12 million tonnes of CO₂ have been stored. The way the CO₂ spreads under ground has been monitored in various research projects which are funded in part by the EU.

It started in 1990 with the choice of the conceptual solution for the Statoil-operated Sleipner West gas and condensate field in the North Sea, when it was still at the planning stage. Tests showed that the natural gas in the reservoir contained around 9% carbon dioxide. This exceeded the customers' requirements and the carbon dioxide content therefore had to be reduced.

In 1991, the Norwegian government introduced a CO₂ tax to reduce emissions offshore. The quotas and CO₂ tax now total about USD 50 per tonne.

The carbon dioxide tax was one of the reasons for Statoil's plans to separate the carbon dioxide offshore and to inject it into geological layers deep beneath the Sleipner platform.

The carbon dioxide will probably remain stored in the geological layer for thousands of years. The layer contains porous sandstone filled with saline water, and it is called the Utsira formation. The CO₂ is contained under an 800-metre thick layer of gas-tight cap rock and cannot seep into the atmosphere.

The Utsira reservoir is continuously monitored using seismology, and comprehensive models have been developed for calculating how the carbon dioxide moves in the reservoir. Seismic testing in June 2008 showed that the storage is proceeding as planned.The Sintef research foundation and the Norwegian University of Science and Technology (NTNU) in Trondheim are involved in addition to several international research institutions.

A number of articles have been published on the basis of data from Sleipner, and Statoil has proposed guidelines for a legal framework for how the carbon storage is to be monitored.  In December 2008 the EU took a big step forward with regard to the framework for CCS and has thus become a model for other countries and regions.