Underground geological formations have more space to store CO2 than we’ll ever need, by orders of magnitude. But the process of assessing the best locations can take up to ten years, so that work needs to start now, say Raimund Malischek and Samantha McCulloch at the IEA. The main constraints are technical (which porous rock formations absorb CO2 most easily, etc.), while the displacement of land use and public acceptance must also be considered. Location is the least of the problems: most CO2 emitting regions have potential underground storage within 100km, explain the authors. They point at existing carbon storage projects, and look at the risk of leakage (low) and the monitoring that will be needed. CO2 could be turned into other chemicals and fuels, avoiding the need for storage, but the global demand for such products will never come close to using up the billions of tonnes emitted every year. The IEA has examined the opportunity for CO2 storage in three key regions, the U.S., Europe and China. Storage costs are low. In the U.S. it’s typically less than $20/tonne. The cost of the other half of the CCS equation – the carbon capture – needs to come down drastically and hopefully will do so over the next decade. By then we’ll need to know where to store it, which is why governments and industry must scale up their location research to match that timescale, say the authors.
Carbon capture, utilisation and storage (CCUS) will need to be a key pillar in successful clean energy transitions. It is the only group of technologies that contributes both to directly reducing emissions in critical economic sectors and to removing CO2 to balance emissions that cannot be avoided – a balance that is at the heart of net-zero emission goals.
CO2 storage is a crucial component of the CCUS value chain. While CO2 can be captured from a range of sources – including from fossil- and biomass-based power generation, industrial processes and directly from the air – permanently storing this CO2 is the essential enabler of large-scale emissions reductions. Technology-based approaches to removing carbon from the atmosphere critically depend on CO2 storage for “negative emissions”.
In IEA analysis of net-zero pathways, the need for CO2 storage grows from around 40 Mt/year today to more than 5,000 Mt/year by mid-century. Carbon management services – transporting and storing CO2 in large quantities – would become a global industry supporting emissions reductions across multiple parts of the energy system.
CO2 has been safely stored for decades
CO2 can be stored in deep geological formations in a process that mimics how oil and gas have been trapped underground for millions of years. Captured CO2 is compressed and injected deep beneath the earth’s surface into a reservoir of porous rock located under an impermeable layer of rock (known as a cap-rock). This acts as a seal. The CO2 is prevented from migrating to the surface by the cap rock as well as other “trapping mechanisms” related to how the CO2 behaves in the subsurface. Several types of reservoir are suitable for CO2 storage, with deep saline formations and depleted oil and gas reservoirs having the largest capacity.
The first large-scale CO2 capture and injection project with dedicated CO2 storage and monitoring was commissioned at the Sleipner offshore gas field in Norway in 1996. The project has now stored more than 20 Mt of CO2 in a deep saline formation, equivalent to taking around 4.3 million passenger vehicles off the road for one year. A further project in Norway (Snøhvit) and projects in Canada (Quest), the United States (Illinois Industrial) and Australia (Gorgon) have increased storage capacity to around 8 Mt per year. Operators of oilfields use and incidentally store a further 34 Mt of CO2 through enhanced oil recovery.
Concerns that CO2 stored underground could leak has raised questions about the effectiveness of CCUS as a climate mitigation measure as well as potential safety risks. Decades of experience with large-scale CO2 storage have demonstrated that risks of leakage are small and can be managed effectively, but careful storage site selection and appraisal are critical, together with comprehensive CO2 monitoring systems.
Potential storage capacity is well in excess of what will be needed
High-level geological analysis suggest that the world has ample CO2 storage capacity. Using geospatial data on sedimentary thickness and other parameters, total global storage capacity has been estimated at between 8,000 Gt and 55,000 Gt.
Even the lowest estimates far exceed the 220 Gt of CO2 that is stored over the period 2020‑2070 in the IEA Sustainable Development Scenario. The vast majority of the estimated capacity is onshore in deep saline formations and depleted oil and gas fields, but there is also significant offshore capacity, ranging from 2 000 Gt to 13 000 Gt.
Some constraints on location
Of course, not all potential storage capacity will be accessible or commercially viable. Factors such as land use constraints and public acceptance will determine where CO2 storage sites can be developed. Technical factors relating to the geology will also act as a constraint on ultimate capacity, for example the quality of the cap rock or the rate at which the CO2 can be injected. These and other factors must be carefully assessed as part of the site selection process.
…but not many
The availability of storage differs considerably across regions, with the Russian Federation, North America and Africa holding the largest capacities. Substantial capacity is also thought to exist in Australia. Despite the stark regional variations in storage capacity, only a few countries might face a shortfall in domestic storage capacity over the period to 2070.
Almost 70% of emissions are within 100 km of potential storage in key regions
- The United States is the leader in global CCUS deployment, home to more than 60% of current CCUS capacity and around 50% of capacity under development.
- Europe is progressing significant CCUS development in the North Sea and around CCUS hubs. In September 2020 the Norwegian government committed USD 1.8 billion to the Longship CCS project, which includes the “Northern Lights” CO2 transport and storage hub, and the UK government has announced GBP 1 billion to establish CCUS in four industrial regions.
- And in the People’s Republic of China, which accounts for around one-third of global emissions today, the 2060 carbon neutrality target announced in September 2020 is already providing a major push for CCUS.
Detailed geospatial analysis shows that around 70% of power and industrial emissions in China, Europe and the United States are within 100 km of potential storage. For comparison, in the United States, CO2 captured at existing facilities is transported an average of 180 km via pipeline today.
The proximity of storage to emission sources, where feasible clustered around CCUS hubs with shared infrastructure, will be a crucial factor in reducing costs, decreasing infrastructure development times and enabling a rapid rollout of CCUS.
Storage costs can be very low or even negative
The cost of CO2 storage can vary greatly on a case-by-case basis, depending on the rate of CO2 injection and the characteristics of the storage reservoirs, as well as their location.
The cost of onshore storage in the United States shows a large spread. However, more than half of onshore storage capacity is estimated to be available below USD 10/t CO2.
In some cases, storage costs can even be negative if the CO2 storage is associated with enhanced oil recovery, generating increased revenue from oil sales.
Can the CO2 be used instead? Yes, but not nearly enough
New opportunities to use CO2 in the production of fuels, chemicals and building materials are emerging and could play an important role in meeting climate goals. These opportunities are another tool in the climate toolbox, but are not an alternative to large-scale geological storage in net-zero pathways.
In a scenario with limited availability of CO2 storage, CO2 use within the energy system increases, but delivers less than 13% of the emissions reductions that would otherwise be provided by CO2 storage. This reflects the fact that in most applications the CO2 is ultimately emitted, for example when the fuel is combusted. By extension there is limited potential for CO2 use to support carbon removal.
Governments and industry have the power to accelerate CO2 storage development
IEA analysis highlights that billions of tonnes of CO2 will need to be stored in a net-zero pathway, but this is dependent on identifying and developing the world’s vast geological storage resources.
While notional CO2 storage volumes are vast, not all of this capacity will prove to be technically and commercially feasible. Most regions need significant further site characterisation and exploration to identify, assess and develop CO2 storage resources so that the capacity is available when it is needed. The process of characterising and assessing CO2 storage can be lengthy – up to ten years depending on existing data – underscoring the need for early action from government and industry.
CO2 storage development will also need to be supported by robust legal and regulatory frameworks and improved public awareness and acceptance. The IEA will continue to work closely with industry and governments to share global experience and best practices for CO2 storage development, with a new report on developing CO2 storage resources to be published in 2021.
Raimund Malischek is an Energy Analyst at the IEA
Samantha McCulloch is the Head of Carbon Capture Utilisation and Storage Unit at the IEA
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