The buyers of Sleipner gas have set restrictions on its CO2 content. The CO2 level in the produced natural gas from the Sleipner field is too high in relation to the buyers’ requirements. This is why CO2 is captured on the Sleipner field before it is reinjected and stored in the bedrock.

The capture takes place using a conventional amine process. The storage on Sleipner has been ground-breaking on a global scale and has provided Statoil with considerable expertise and experience within geological CO2 storage.

In 1990, in connection with the concept solution for the gas and condensate field Sleipner West in the North Sea, it became clear that the natural gas in the reservoir contained about 9 per cent CO2, which far exceeded the customers’ requirements. The CO2 content therefore had to be reduced.

In 1991, the Norwegian authorities introduced a CO2 tax as an effort to reduce emissions of CO2 from Norwegian offshore oil and gas activities. In 2013, the price of quota purchases and CO2 tax is about USD 50 per tonne. The extra necessary investments in order to compress and reinject CO2 amounted to approx. USD 100 million (1996).

The CO2 tax was one of the triggers for Statoil’s plans to separate the CO2 gas offshore and inject it in deeper geological layers under the CO2 platform.
By early 2013, a total of more than 14 million tonnes of CO2 from Sleipner’s gas production had been stored.

The CO2 gas will remain in the geological layer for thousands of years. The layer contains porous sandstone filled with saltwater, and is called the Utsira formation. The CO2 gas is trapped under an 800-metre thick layer of ceiling rock and will therefore not seep into the atmosphere.

Statoil has been focused on sharing information and experience from Sleipner. In addition to a number of international research institutions, the Norwegian institutions SINTEF and NTNU have been deeply involved in research surrounding Sleipner.

The subsurface storage of CO2 has been mapped in various research projects, some of which are partly funded by the EU. Seismic surveys and other measurements show that the storage and extent of CO2 underground are in line with the plans established prior to injection. Several articles have been published based on data from Sleipner.

Statoil’s experience with Sleipner has also led to Statoil’s active participation by advising on the regulatory framework concerning the storage of CO2, both nationally and internationally.