Sleipner West

Location and Geology

• The Sleipner West field is situated in the North Sea, specifically in blocks 15/6 and 15/9.
• The field's reservoirs are primarily in the Middle Jurassic Sleipner and Hugin Formations, with depths of approximately 3,450 meters. The Hugin Formation contains most of the reserves, and the faults in the field are generally not sealed, allowing good communication between the sand deposits.

Production and Infrastructure

• Production from Sleipner West began in 1996.
• The field is developed with the Sleipner B wellhead platform, which is an unmanned platform operated and maintained from the Sleipner A platform via helicopter. The wellstream from Sleipner B is transported through a 12-kilometer pipeline to the Sleipner T platform for processing and gas treatment.
• Sleipner T platform is connected to Sleipner A via a permanent bridge and is responsible for CO2 removal from the wellstream. The CO2 is then injected into the Utsira Sand formation for storage.

Carbon Capture and Storage (CCS)

• The Sleipner West field is notable for its pioneering use of CCS technology. The natural gas produced contains around 4-9.5% CO2, which must be reduced to less than 2.5% to meet commercial specifications. Since 1996, the project has been separating and storing this excess CO2, injecting approximately 1 million tonnes per year into the Utsira Sand formation, a shallow saline aquifer.
• The CCS project was motivated by Norway's carbon tax introduced in 1991, making it financially viable to store CO2 rather than venting it into the atmosphere. By the end of 2022, over 19 million tonnes of CO2 had been stored.

Technical and Operational Details

• The CO2 is separated using amine scrubbers at the Sleipner T platform and then injected into the Utsira Sand formation via a single deviated well. The injection point is approximately 1,012 meters below sea level, about 200 meters below the reservoir top.
• The CO2 is injected in a dense phase, with temperature and pressure controls at the wellhead to maintain stable conditions. The monitoring program includes time-lapse seismic imaging and pressure monitoring to track the CO2 plume.

Economic and Regulatory Context

• The project's total capital cost was estimated at $300 million, with operating costs of about $0.75 million per year. The costs are offset by the savings from avoiding the Norwegian carbon tax, which was $51 per tonne of CO2 in 1991 and increased over time.
• The Sleipner CCS project has been a key reference for the technical and regulatory development of CO2 storage in Europe, influencing the EU’s Directive on geological storage of CO2.

Tie-in Fields and Gas Hub

• Sleipner West is part of a larger gas hub that processes hydrocarbons from several tie-in fields, including Sigyn, Volve, Gudrun, and Gina Krog. The gas is exported through the Gassled pipeline infrastructure, and unstable condensate is transported to Kårstø for further processing and export.

Contractors and Maintenance

• Several contractors have been involved in the development and maintenance of the Sleipner West field, including ABB, Kvaerner, Aibel, Emtunga, Heerema Marine Contractors, and Saipem.

In summary, the Sleipner West gas and condensate field is a significant project in the North Sea, known for its pioneering use of CCS technology, robust gas processing infrastructure, and its role as a major gas hub in the region.