Sleipner Project

The Sleipner Project is a pioneering carbon capture and storage (CCS) initiative located in the North Sea, off the coast of Norway. Operated by Equinor ASA (formerly Statoil), it is the world’s first commercial-scale offshore CCS project, initiated in 1996. The project captures carbon dioxide (CO₂) produced during natural gas extraction and permanently stores it deep beneath the seabed, preventing its release into the atmosphere.
The Sleipner Project represents a major technological and environmental milestone in global efforts to mitigate climate change and reduce greenhouse gas emissions, serving as a model for future carbon storage projects worldwide.

Location and Geological Setting

The Sleipner field is situated in the central North Sea, about 250 kilometres west of Stavanger, Norway, within the Norwegian continental shelf. It is part of the Sleipner gas field complex, which includes Sleipner East, Sleipner West, Gungne, and Gudrun fields.
The captured CO₂ is injected into a deep saline aquifer known as the Utsira Formation, located approximately 800–1,000 metres beneath the seabed.

• The Utsira Formation is composed mainly of porous sandstone, overlain by impermeable shale layers that act as a seal to trap the CO₂ securely.
• The storage capacity of the formation is estimated to be over 500 billion tonnes of CO₂, far exceeding Norway’s current emission levels.

Background and Objectives

The Sleipner Project originated as a response to Norway’s carbon tax on offshore oil and gas production, introduced in 1991. The tax made it economically viable for Equinor to capture and store CO₂ rather than emit it into the atmosphere.
Natural gas extracted from the Sleipner field contains approximately 9% CO₂, which must be removed to meet commercial specifications (less than 2.5% CO₂) before being exported. Instead of venting the separated CO₂, the project injects it into the subsurface Utsira aquifer.
Primary Objectives:

• To reduce CO₂ emissions from natural gas production.
• To demonstrate the technical feasibility and safety of large-scale CO₂ storage.
• To comply with Norway’s environmental regulations and carbon tax framework.
• To contribute to climate mitigation by developing sustainable carbon management practices.

Technical Process and Operation

The Sleipner CCS system involves three main stages: separation, compression, and injection.
1. CO₂ Separation:

• At the Sleipner T platform, natural gas from the reservoir is processed to remove CO₂ using an amine-based absorption system.
• The CO₂-rich gas is separated from methane and other hydrocarbons.

2. Compression and Transport:

• The captured CO₂ is compressed to a supercritical state (behaving as both a liquid and a gas) for efficient transport and injection.
• It is then directed via pipelines from the processing platform to the injection well.

3. Injection and Storage:

• The compressed CO₂ is injected into the Utsira Formation at depths of about 1 kilometre below the seabed.
• Once injected, the CO₂ gradually migrates within the porous sandstone, trapped by overlying impermeable rock layers and through processes such as structural trapping, residual trapping, and mineralisation.

The project stores approximately 1 million tonnes of CO₂ per year, making it one of the most successful and longest-running CCS operations in the world.

Monitoring and Verification

Monitoring is a crucial component of the Sleipner Project to ensure that the CO₂ remains securely stored and does not leak to the surface or into the ocean.
Techniques used include:

• Seismic Surveys: 3D and 4D seismic imaging is used to track the distribution and movement of CO₂ within the Utsira Formation over time.
• Gravimetric and Pressure Monitoring: Changes in subsurface pressure and density are measured to detect potential leaks or anomalies.
• Geochemical Sampling: Regular sampling of formation fluids helps verify the stability of CO₂ and assess any chemical interactions with the rock.

These monitoring systems have shown that the CO₂ remains safely contained within the reservoir, with no detectable leakage after more than two decades of operation.

Environmental and Economic Significance

1. Climate Change Mitigation: The Sleipner Project prevents about 1 million tonnes of CO₂ emissions per year from entering the atmosphere—equivalent to the annual emissions of roughly 200,000 cars. It demonstrates that carbon capture and storage can play a vital role in achieving net-zero emission goals.
2. Cost and Efficiency: The project’s capital and operational costs are offset by the savings from avoiding Norway’s CO₂ tax, which was one of the highest in the world at the time.

• Estimated storage cost: US$17 per tonne of CO₂ (approximate).
• Operational efficiency and reliability have made Sleipner a benchmark for CCS economics.

3. Environmental Safety: Continuous monitoring confirms that CO₂ remains securely stored without leakage, validating the long-term safety of geological storage.
4. Technological Innovation: Sleipner provided valuable data on reservoir behaviour, fluid dynamics, and monitoring techniques, leading to improved CCS modelling and design worldwide.

Global Importance and Replication

The Sleipner Project’s success inspired the development of numerous CCS initiatives globally, including:

• Snøhvit Project (Norway): Another offshore CO₂ storage project begun in 2008.
• In Salah Project (Algeria): Onshore CO₂ injection into deep saline aquifers.
• Gorgon Project (Australia): One of the world’s largest CCS operations.
• Quest Project (Canada): Captures CO₂ from oil sands upgrading.

Sleipner serves as a prototype for integrating CCS technology with fossil fuel operations and as a model for future decarbonisation strategies.

Challenges and Lessons Learned

While Sleipner is widely considered a success, it has also highlighted several challenges in large-scale CCS implementation:

• High initial investment and operating costs.
• Public perception and environmental concerns regarding long-term CO₂ storage.
• Regulatory and policy uncertainty in some regions.
• Limited global carbon pricing mechanisms to incentivise widespread adoption.

However, its demonstrated technical viability, environmental safety, and policy alignment have shown that CCS can be an essential part of global efforts to reduce industrial emissions.

Contribution to Research and Policy

The project has provided a vast amount of scientific and engineering data, contributing to international understanding of geological CO₂ storage.It supports global climate initiatives under frameworks such as the Kyoto Protocol and the Paris Agreement, aligning with Norway’s national climate strategy and the European Union’s emission reduction goals.
The Sleipner dataset is one of the most studied in the world, widely used in CCS research and modelling. It has become a cornerstone for developing international regulations, safety standards, and best practices for carbon storage.