Sleipner gas field
| Company type | Offshore natural gas field |
|---|---|
| Industry | Oil and gas industry |
| Founded | 1974 (Sleipner West), 1981 (Sleipner East) |
| Headquarters | Norway |
Area served | North Sea |
Key people | Equinor (operator) |
| Products | Natural gas, light oil condensates, natural gas liquids |
The Sleipner gas field is situated in block 15/9 of the North Sea, roughly west of Stavanger, Norway. It consists of two distinct production zones: Sleipner West, discovered in 1974, and Sleipner East, identified in 1981. This field yields natural gas along with light oil condensates extracted from sandstone reservoirs located approximately below the ocean surface. Managed by Equinor, Sleipner holds a pivotal position within Norway's offshore energy industry. The name derives from Sleipnir, the eight-legged steed belonging to the Norse deity Odin.
Reserves and production
By the close of 2005, the combined recoverable reserves for Sleipner West and East were estimated at 51.6 billion cubic meters of natural gas, 4.4 million tons of natural gas liquids, and 3.9 million cubic meters of condensates. In 2008, daily output averaged around 300,000 barrels of oil equivalent, including 36 million cubic meters of natural gas and 14,000 cubic meters of condensate. According to a 2017 assessment by the Norway Petroleum Directorate, remaining reserves were approximated at 2.72 million cubic meters of oil, 11.72 billion cubic meters of natural gas, 0.67 million tons of natural gas liquids, and 0.07 million cubic meters of condensates.
The field operates through four platforms servicing a total of 18 production wells. Sleipner A is positioned on Sleipner East, whereas Sleipner B is located on Sleipner West and controlled remotely via an umbilical cable from Sleipner A. The Sleipner T platform, dedicated to carbon dioxide treatment, connects to Sleipner A by a bridge and links to Sleipner B through a 12.5 km CO2 pipeline. Additionally, the Sleipner Riser platform supports the Langeled and Zeepipe pipeline systems on the Sleipner East section.
Carbon capture and storage project
The Sleipner Vest area hosts the globe’s inaugural offshore carbon capture and storage (CCS) installation, which has been operational since September 1996. Early operational difficulties caused by subsiding top sand layers were addressed in 1997 through re-perforation and gravel placement.
As reported by Equinor in 2018, approximately one million tonnes of CO2 have been injected yearly into the Utsira formation beneath the seabed since the project began. Nevertheless, between 2017 and 2019, Equinor acknowledged that CO2 sequestration volumes had been overestimated by roughly 30% due to faults in monitoring equipment. The facility is reported to have a storage capacity reaching up to about 600 billion tonnes.
CO2 levels in the Sleipner West field reach up to 9%, exceeding Norway’s export threshold limit of 2.5%, resulting in operating expenses near US$17 per ton injected. The company benefits from exemptions on Norway’s carbon taxation and gains credits under the EU Emissions Trading Scheme.
Captured CO2 is processed aboard the Sleipner T platform before being piped to Sleipner A for injection into the Utsira saline aquifer roughly 1000 meters beneath sea level. Continuous monitoring employing time-lapse gravity and seismic techniques has verified secure CO2 containment without any leaks or seismic activity for over ten years.
Since 2014, regulatory oversight under Norway’s petroleum legislation combined with compliance to EU directives ensures ongoing reservoir integrity and environmental protection. Geochemical simulations forecast long-term CO2 entrapment through dissolution and mineralization within stratified clay and sand layers aided by groundwater movement.
Gassco has proposed constructing a 240 km pipeline from Kårstø intended for CO2 transport from the retired Kårstø power plant. While injection pipelines are resistant to corrosion during CO2 transport, transmission pipelines face challenges such as dew formation that can cause rust under conditions of low temperature and high pressure.
Miocene Utsira Formation
The Miocene Utsira Formation represents an extensive aquifer confined by consistent, stratified clay layers. Its development occurred in several stages associated with sea-level fluctuations during the Pliocene, with sedimentation spanning from the late Miocene and early Pliocene through to the early Pleistocene, as evidenced by palynology studies. The formation is overlain by deltaic sands from the upper Pliocene, with the shallowest sand layers located approximately 150 meters below sea level. Through analysis of 3D seismic data, it has been established that the Utsira sandstone lies beneath a marine sediment cover ranging from 800 to 1000 meters thick, with sandstone thicknesses exceeding 300 meters in places. Geographically, the formation extends about 450 kilometers in a north-south direction and 90 kilometers east-west. Thick sand deposits are primarily concentrated in the northern and southern sectors, while thinner sediment layers are distributed across the central seabed. The northern Tampen region features sparse glauconitic sand deposits.