Subsea Carbon Capture

Subsea carbon capture helps to reduce greenhouse gas emissions and mitigate climate change by safely and securely storing captured carbon dioxide (CO₂) deep beneath the ocean's surface. Geological formations beneath the ocean floor provide vast storage capacity, allowing large quantities of CO₂ to be stored for extended periods. Additionally, the ocean acts as a natural barrier, reducing the risk of CO₂ leakage to the atmosphere and minimising potential environmental impacts.

What is subsea carbon capture?

Subsea carbon capture refers to the process of capturing CO₂ emissions from industrial sources, such as power plants or heavy industries, and storing them deep beneath the ocean's surface. It is an innovative approach to carbon capture and storage (CCS) that takes advantage of the natural characteristics of the ocean for long-term storage of captured CO₂.

The subsea process

The subsea carbon capture process typically involves three main steps: capture, transportation, and storage. In the capture phase, CO₂ emissions are captured from industrial processes using various technologies such as absorption, adsorption, or membrane separation. Once captured, the CO₂ is compressed and prepared for transportation.

The captured CO₂ is then transported from the capture site to subsea injection wells through dedicated pipelines. These pipelines are designed to withstand the high pressures and corrosive nature of CO₂. Advanced engineering techniques ensure the safe and efficient delivery of CO₂ to the injection sites.

Next, the captured CO₂ is injected into carefully selected geological formations, such as depleted oil and gas reservoirs or saline aquifers, deep beneath the ocean floor. These geological formations provide secure and permanent storage for the CO₂, preventing its release into the atmosphere.

Subsea storage infrastructure

Effective subsea storage projects require a developed infrastructure capable of dealing with the challenges of both CO₂ transport and storage, and deep-sea conditions.

An extensive pipeline network is crucial to connect CO₂ capture sites with subsea injection wells, and must be designed to handle high pressures, corrosive conditions, and long distances. Subsea injection wells, located in geologically suitable formations, are needed to store CO₂ securely and permanently.

Comprehensive monitoring and verification systems ensure the integrity of the subsea storage infrastructure, continuously assessing storage reservoirs, detecting any potential leaks or anomalies, and verifying the effectiveness of storage operations. Recent studies, such as those conducted by scientists from Plymouth Marine Laboratory, have demonstrated that subsea monitoring is both effective and cost-efficient.

Benefits of subsea carbon capture

Subsea carbon capture provides the same benefits as other carbon capture and storage techniques, such as greenhouse gases reduction, large-scale capture, and carbon footprint off-setting. However, there are additional advantages in terms of storage capacity and secure storage that make subsea projects particularly desirable.

Greenhouse gas reduction

By capturing and storing CO₂ deep beneath the ocean's surface, subsea carbon capture prevents the release of CO₂ into the atmosphere, where it would otherwise contribute to global warming and climate change. This technology helps towards efforts to build a sustainable future by mitigating the impacts of greenhouse gas emissions from industrial sources.

Large-scale emissions capture

Subsea carbon capture has the potential to capture significant amounts of CO₂ emissions from various industrial sources, including power plants, refineries, and heavy industries. Its scalability makes it a viable solution for addressing emissions on a substantial scale. By capturing a significant portion of industrial CO₂ emissions, subsea carbon capture helps to decarbonise key sectors and achieve emission reduction targets.

Storage capacity

Subsea carbon storage provides the potential for vast storage capacity of CO₂. Depleted oil and gas reservoirs, saline aquifers, and other geological formations on the ocean floor can serve as storage reservoirs, offering ample space to accommodate large volumes of captured CO₂. These geological formations have proven track records of securely storing hydrocarbons over millions of years, and will have been thoroughly characterised and assessed during their production phase. This scalable capacity of subsea carbon storage enables the capture and storage of emissions from multiple industrial sources at a significant level.

Challenges of subsea carbon capture

While subsea carbon storage offers substantial benefits for global efforts to reduce greenhouse gas emissions and mitigate climate change, using the technique involves a number of challenges which need to be overcome. These include technical and operational issues, financial considerations, and the requirement to work within regulatory frameworks.

Technical and operational challenges

Comprehensive geological and geophysical assessments are crucial to identify reservoirs with adequate storage capacity, structural integrity, and sealing properties. Site characterisation studies and risk assessments are essential to minimize the potential for CO₂ leakage or adverse environmental impacts.

Once a suitable site has been located, infrastructure – such as pipelines – capable of safely and efficiently transporting CO₂ over long distances, often from onshore to offshore, must be established. This is a significant operational challenge requiring careful planning, engineering expertise, and adherence to stringent safety standards.

Injecting CO₂ into subsea storage reservoirs requires careful planning and monitoring. It is essential to ensure proper injection rates, pressures, and distribution of CO₂ within the reservoirs to avoid leakage. Robust monitoring systems must be in place to detect any potential integrity breaches, confirm storage capacity, and verify long-term containment.

Economic viability and cost-effectiveness

The initial capital investment required for establishing subsea carbon storage infrastructure, along with ongoing operating and maintenance costs, can be significant. Developing the necessary infrastructure involves substantial expenditure, while the need for specialised equipment and engineering expertise adds to the overall expense. These high upfront costs pose a challenge to the economic viability of subsea carbon storage projects.

The economic viability of subsea carbon storage depends on the scale of emissions capture – a sufficient quantity of CO₂ must be captured and stored to achieve cost-effectiveness. The ability to capture emissions at a large scale from multiple industrial sources is crucial to improving cost-effectiveness.

Subsea carbon storage also faces competition from alternative CCS technologies, such as onshore storage or utilisation options. Comparing the costs and benefits of subsea carbon storage with other CCS methods is crucial to determine its economic viability.

Environmental and regulatory considerations

Subsea carbon capture projects must adhere to stringent environmental regulations and undergo comprehensive environmental impact assessments. These considerations ensure the protection of marine ecosystems and biodiversity while also minimising the potential risks associated with storing CO₂ in subsea reservoirs. Collaborative efforts among governments, industry stakeholders, and environmental organisations are essential to strike the right balance between climate goals and environmental protection.