The Science of Carbon Storage: Safeguarding CO2 for the Long Term

01 Oct 2024

12 Min Read

Dr Firnaaz Ahamed (Academic Contributor), The Taylor's Team (Editor)

IN THIS ARTICLE

In the fight against climate change, reducing carbon emissions alone may not be enough. As global temperatures continue to rise, the need for innovative solutions to manage and mitigate the impacts of excess carbon dioxide (CO₂) in our atmosphere has never been more urgent. One such solution gaining traction is carbon storage, a process that involves capturing CO₂ emissions and storing them securely underground for the long term. This technology, often referred to as carbon sequestration, is increasingly seen as a critical component of global strategies to limit warming to 1.5°C above pre-industrial levels.

But how do we ensure that the CO₂ we bury deep beneath the Earth's surface stays there, safeguarding our future?

The Basics of Carbon Storage

At its core, carbon storage is a process designed to prevent CO₂ from entering the atmosphere, where it would contribute to the greenhouse effect and global warming. Instead, CO₂ is captured from sources such as power plants, industrial facilities, or directly from the air, and then transported to a storage site where it is injected deep underground into geological formations. These formations, often composed of porous rock layers overlain by impermeable cap rocks, act as natural reservoirs, trapping the CO₂ and preventing it from migrating back to the surface.

There are several methods of carbon storage, each with its unique approach to securing CO₂. Geological sequestration, by far the most prevalent, involves storing CO₂ in deep saline aquifers, depleted oil and gas fields, or unmineable coal seams. Ocean storage, though less common due to environmental concerns, involves dissolving CO₂ in seawater or injecting it into the deep ocean floor.

Another emerging technique is mineralisation, where CO₂ reacts with certain types of rocks to form stable carbonates, effectively locking the carbon away in a solid, inert form. Soil carbon sequestration (SCS) is another emerging process that stores carbon in soil carbon pools, primarily mediated by soil microbial communities. By managing the composition and activity of these soil microbes, the capacity of soil to sequester carbon can be enhanced. This not only boosts carbon storage but also enhances soil fertility, and maintains essential ecosystem services, promoting long-term soil health and sustainability.

By capturing and securely storing CO₂, we can offset emissions from sectors that are difficult to decarbonise, such as heavy industry and aviation. This makes carbon storage an essential tool in the broader effort to reduce atmospheric CO₂ levels and combat climate change. Yet, while the concept is straightforward, the execution is anything but, requiring sophisticated technology and careful management to ensure long-term effectiveness.

Advancements in Carbon Storage Technology

As the urgency to address climate change intensifies, so too does the need for more sophisticated and reliable carbon storage technologies. Recent advancements in the field have focused on improving the efficiency of CO₂ capture, enhancing the security of storage, and developing more precise monitoring systems to ensure that stored CO₂ remains safely underground for the long term.

One of the most significant areas of progress has been in CO₂capture technology. Traditional methods, such as post-combustion capture (PCC), have been supplemented by innovative approaches like direct air capture (DAC), which involves extracting CO₂directly from the atmosphere. This technology, while still in its early stages, holds promise for achieving negative emissions, a critical goal in scenarios where reducing atmospheric CO₂ is necessary. Advancements in chemical solvents and solid sorbents also have made the capture process more energy-efficient, reducing the overall cost and environmental impact.

_{Figure from Meckling, J., Biber, E. A policy roadmap for negative emissions using direct air capture. Nat Commun 12, 2051 (2021). Licenced under CC BY 4.0.}

Enhancing the storage capacity and security of geological formations has also seen considerable progress. Researchers are exploring the use of advanced materials, such as CO₂-reactive minerals, which can enhance the natural trapping mechanisms within the rock formations.

These materials can accelerate the process of mineralisation, where CO₂ is converted into stable carbonates, effectively locking it away in a solid form. Moreover, new reservoir management strategies, including the controlled injection of CO₂ in combination with other gases, are being tested to optimise storage efficiency and minimise the risk of leakage.

Perhaps the most critical advancement, however, lies in the monitoring and verification of stored CO₂. State-of-the-art technologies, such as 4D seismic imaging and fibre optic sensing, allow for real-time tracking of CO₂ movements within the storage site. These tools provide a detailed picture of the subsurface environment, enabling operators to detect any potential leaks or anomalies early on.

Additionally, satellite-based monitoring systems and surface sensors have been developed to complement subsurface techniques, ensuring comprehensive oversight of storage sites. The integration of artificial intelligence and machine learning into these monitoring systems further enhances their ability to predict and prevent any issues, making carbon storage safer and more reliable.

Case Studies of Successful Carbon Storage Projects

Around the world, several carbon storage projects have demonstrated the feasibility and effectiveness of geological sequestration, providing valuable insights and setting benchmarks for future initiatives.

_{The Sleipner field in the North Sea. Photo from Equinor ASA}

One of the most well-known examples is the Sleipner CO₂ Storage Project in the North Sea, operated by Equinor. Since 1996, this project has been successfully capturing and storing approximately one million tonnes of CO₂ annually from natural gas processing. The CO₂ is injected into the Utsira Formation, a deep saline aquifer located about 800 - 1,000 metres beneath the seabed. Over the years, Sleipner has become a flagship project for carbon storage, demonstrating the long-term viability of geological sequestration and serving as a model for similar initiatives worldwide. The success of this project has also provided invaluable data on CO₂ behaviour in underground formations, helping to refine predictive models and improve storage techniques.

_{Image showing SaskPower Boundary Dam. Licenced under CC BY 4.0.}

Another notable project is the Boundary Dam Carbon Capture and Storage (CCS) Project in Saskatchewan, Canada. Launched in 2014, Boundary Dam is the world’s first large-scale CCS project at a coal-fired power plant. The project captures up to one million tonnes of CO₂ annually, which is then used for enhanced oil recovery (EOR) in nearby oil fields or stored in deep geological formations. This dual approach not only reduces emissions from the power plant but also supports the production of oil, making it economically viable. Boundary Dam has been instrumental in proving that CCS can be effectively integrated into existing industrial processes, offering a pathway for other carbon-intensive industries to reduce their emissions.

_{Image obtained from International Energy Agency.}

In Asia, the Tomakomai CCS Demonstration Project in Hokkaido, Japan, is a significant example of offshore geological storage. Launched in 2016 by Japan CCS Co, this project captures CO₂ from a hydrogen production unit at an oil refinery and stores it in geological formations beneath the seabed. The CO₂ is injected into two different formations: one in a sandstone layer and another in a volcanic rock layer, both about 1,000 metres below the seabed. By 2020, the project had successfully stored over 300,000 tonnes of CO₂, demonstrating the feasibility of offshore geological storage in Japan’s complex geological environment. Tomakomai has been a pivotal project in proving that CCS can be effectively implemented in regions with challenging geological conditions, contributing valuable data to global CCS research.

Dr Jasmine Jain

Carbon storage solutions often require integrating diverse expertise to address the complex interplay of biological, chemical, environmental processes. Collaboration across these fields fosters holistic approaches that enhance the scalability and sustainability of carbon storage efforts.

Dr Firnaaz Ahamed

Lecturer, School of Engineering

The Role of Carbon Storage in Combating Climate Change

As the world intensifies its efforts to mitigate the impacts of climate change, carbon storage is emerging as a crucial component of the global strategy to reduce atmospheric CO₂ levels. While transitioning to renewable energy sources and improving energy efficiency are essential steps, these alone may not be sufficient to achieve the deep emissions reductions required to meet international climate targets. This is where carbon storage plays a pivotal role, providing a means to manage emissions from sectors that are particularly challenging to decarbonise.

One of the most significant contributions of carbon storage is its ability to complement renewable energy initiatives. Even as the world shifts towards solar, wind, and other renewable energy sources, there are still industries—such as cement, steel, and chemical manufacturing—where CO₂ emissions are difficult to eliminate entirely due to the nature of their processes. Carbon storage offers a solution for these hard-to-abate sectors by capturing and sequestering the CO₂ they produce, effectively reducing their carbon footprint.

A large, modern petrochemical plant at dusk in industrial district near Rotterdam, Netherlands, Benelux, Europe

In addition to addressing emissions from industrial sources, carbon storage also supports the concept of negative emissions, which are increasingly recognised as necessary for limiting global warming to 1.5°C. Negative emissions can be achieved through technologies like direct air capture, which extracts CO₂ directly from the atmosphere and stores it underground. By actively removing CO₂ from the air, carbon storage can help offset emissions that are difficult or impossible to eliminate, making it an essential tool for achieving net-zero emissions.

The long-term impact of carbon storage on global CO₂ levels is profound. By securely storing billions of tonnes of CO₂ underground, this technology can significantly slow the accumulation of greenhouse gases in the atmosphere, buying time for other mitigation efforts to take effect. Moreover, as carbon storage technology continues to advance, its scalability and cost-effectiveness are expected to improve, making it an increasingly viable option for countries around the world.

However, the success of carbon storage in combating climate change also depends on strong policy support and international collaboration. Governments and industries must work together to develop and implement the necessary regulatory frameworks, financial incentives, and infrastructure investments to scale up carbon storage efforts. This includes fostering global partnerships to share knowledge, technology, and best practises, ensuring that carbon storage can be deployed effectively in diverse geological and economic contexts.

Conclusion

Carbon storage represents a powerful and essential tool in the global effort to combat climate change, offering the means to capture and securely store CO2 for the long term. As we continue to innovate and scale this technology, we are not only safeguarding our planet but also paving the way for a more sustainable future. The challenges ahead are significant, but with collective determination, interdisciplinary collaboration, and bold action, carbon storage has the potential to transform how we address emissions and inspire a new era of climate leadership.

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