The Sleipner Gas field is composed of the Sleipner Vest gas field and the Sleipner Øst condensate gas field. One challenge with production was the high CO2 content (approximately 9 %) in these Gas fields.
Production Facilities
The Sleipner East field is produced by the Sleipner A platform and the Sleipner West field is produced using the Sleipner B platform. There are 18 wells on production in the field. The field is planted with 18 production wells. Sleipner A is a combined accommodations, production and processing offshore platform at the Sleipner East gas field.
Carbon-dioxide treatment is done on the Sleipner T platform using amine technology and after that carbon dioxide is transported by a 12.5 km flow line to the Sleipner B wellhead platform where it is injected to the reservoir.
Utsira Formation
The Utsira Formation is a 200-250 meters thick massive Miocene sandstone. The Utsira Formation is a large aquifer with a stable, layered clay seal. The figure below shows the Utsira sand along with the layered clay seal. The image also shows the large extension of the Utsira formation.
It is estimated that the Utsira Formation is capable of storing 600 billion tons of CO2. 3D seismic monitoring of the CO2 injection into the Utsira Formation shows that there is no leakage of the CO2 into other horizons.
Carbon Tax
The Sleipner CCUS was an effort to the reduce the CO2 emission tax that Equinor would pay on producing gas from the Sleipner fields. The additional investments in order to compress and re-inject the removed CO2 amounted to approximately $100m (USD in 1996).
The offshore industry currently pays CO2 taxes and quotas under the EU Emission Trading System (ETS). For the offshore oil and gas sector the CO2 taxes and the quota price under ETS is currently around $60 (USD) per ton.
CCUS – As a Concept
The natural gas produced from the Sleipner West field contains up to 9% CO2, however, to meet the required export specifications and the customers requirements, this has to be reduced to a maximum of 2.5%. The CO2 is removed from the produced gas at an offshore platform before being pumped back into the ground and the hydrocarbons piped to land.
If this process had not been adopted, and the CO2 produced would be vented off to the atmosphere. This operators would have had to pay NOK 1 million/day in Norwegian CO2 taxes. In may 2008 Statoil had stored over 10 million tons of CO2. There is no evidence of CO2 leakage and the CO2 remains in situ.
This is the longest ongoing project on CO2 storage in the world. Each year about 1 million tonnes CO2 from the natural gas is captured and stored at Sleipner. This has provided unique insight into what happens with carbon stored in the underground over longer periods of time.
The Success Story
The Sleipner CCUS project provides a strong industry standard framework to implement CCUS projects around the world. With increased focus on reduction of greenhouse emissions, insights into the Sleipner CCUS valuable has been for the industry, research communities, and in making CO2 storage a central part of the ongoing energy transition. This project has demonstrated the feasibility of safe long-term storage of CO2 in deep underground formations.
The Sleipner CCUS facility has also begun to process and store CO2 from neighboring gas fields in the Sleipner area. The Sleipner CCS project has received global recognition for its contribution to the development of CCS by receiving several technology awards including the Carbon Sequestration Leadership Forum (CSLF) Global Achievement Award in 2011.
The Inter-Governmental Panel on Climate Change (IPCC) reports of 2007 and 2014 have used the Sleipner CCS project as a landmark to inspire and inform action on climate change mitigation.
Equinor – Open data for the field
The Sleipner 2019 Benchmark Model is a reference dataset from the Sleipner CO2 storage site. . The site has been extensively monitored, and a series of time-lapse seismic datasets that documents the migration of the injected CO2 has been established and (along with associated well logs and baseline seismic) has served as input to the creation of this benchmark model.
The dataset currently available CO2DataShare includes a simulation grid with associated petrophysical properties and well data, as well as velocity maps and individual horizons within the storage reservoir. It was prepared throughout 2018 and 2019, and officially released in January 2020 under the SLEIPNER CO2 REFERENCE DATASET LICENSE, to support research and development into CO2 storage issues.
