In tackling the transition to a low carbon future, many solutions have been proposed. One of these is Carbon Capture and Storage (CCS). In this article we explore CCS and its contribution to the energy transition.
Organic life is carbon-based. All life, from the simplest to the most complex, is composed of carbon, together with some other common elements such as hydrogen, nitrogen and oxygen. Life has been evolving on Earth for billions of years. When organic matter dies, it is typically buried by sediment on land or in rivers, lakes, seas and oceans, or dissolved in the water column. It is thus stored or sequestered.
When organic matter is buried a few kilometres beneath the surface – where sediment accumulates over geological time – it heats up and can transform into different forms of concentrated carbon and hydrogen such as oil and gas (referred to as hydrocarbons). Through natural geological processes associated with tectonic plate movements, some hydrocarbons escape naturally to the surface. Others are trapped and preserved in the deep subsurface where they can be extracted and used as sources of energy. When escaping naturally, or when burned, the hydrocarbons emit carbon-based greenhouse gases such as carbon dioxide (CO²) or methane (CH4).
With growing populations and increasing global industrialisation, energy demand continues to rise, making the task of reducing emissions increasingly challenging. In finding ways to prevent increasing levels of greenhouse gases in the atmosphere, we also need to ensure that the global standard of living and economic wellbeing is maintained. All technologies, existing and developing, need to be marshalled for the challenge. These include energy efficiencies, and the development and deployment, at scale, of renewable energy forms. However, renewable energy production is not growing sufficiently fast to meet the increasing global energy demand, and hence emissions are remaining stubbornly high. Other technologies are needed. CCS provides a real opportunity to capture existing carbon, store it and use it to create energy.
What is CCS?
Carbon is stored in many ways. In addition to burial, as mentioned above, it can exist as vegetation and char on the Earth’s surface, it can be dissolved in water, in solid hydrates in marine environments, or through Carbon Capture and Storage (CCS), and the related Carbon Capture, Utilisation and Storage (CCUS). CCS and CCUS represent a new set of technologies that can safely return the carbon-based emissions back into the subsurface where they resided, in a slightly different form, for tens to hundreds of millions of years, or convert them into new stable solid products.
CCS involves capturing CO 2 generated by large point sources such as power stations and transporting it to a secure underground storage facility, which is typically either a depleted oil/gas field, or a large subsurface aquifer (water-storing layer) of porous and permeable rock. The CO 2 is captured before or after burning in a number of ways (pre-combustion, post-combustion or oxyfuel processes). It is then transported and injected into geological reservoirs that can store it securely on a permanent basis. The injection of CO 2 into oil fields can be used to enhance oil recovery (EOR) as well as to permanently store CO 2.
CO 2 shrinks dramatically when compressed. At a depth of 700m it occupies less than 0.3% of its volume at the surface and hence large volumes can be stored. Reservoirs must be at least 700m beneath the surface, be of large volume, and very porous and permeable. They must have an efficient natural cap rock to seal the stored CO 2 . Depleted oil and gas fields have the potential to be ideal storage sites. There is also huge potential in saline aquifers – porous and permeable rocks that did not contain oil or gas, but rather seawater. The CO 2 can be stored by occupying the pore space (volumetric storage); dissolving in salt water in the reservoir/aquifer (solubility storage); adhering to minerals such as coal (adsorption storage), or combining with other minerals to form new stable minerals (mineral trapping).
With CCUS. the captured CO 2 is utilised, typically through chemical processes, to react with certain minerals or materials and form new, stable and useful products such as aggregates. In essence, these are accelerating naturally occurring chemical processes. For example, the natural weathering of granite at the Earth’s surface involves the chemical breakdown of the mineral feldspar (crystals) to form clay. This clay (kaolin or china clay) is the main ingredient for bone china and pottery. The weathering of feldspar involves the incorporation of CO 2 from the atmosphere into the crystal structure of kaolin/clay and thus permanently stores CO 2 in a stable and useful product. In nature, this process happens slowly but for large-scale CCUS, high concentrations of captured CO 2 are brought into contact with metal oxide-bearing minerals to fix and store the CO 2 as carbonates (the
main components in limestones). Suitable materials for this are certain silicate rocks (e.g. containing serpentine and olivine minerals), or alkaline industrial residues such as slag from steel production or fly ash. In the case of silicate rocks, carbonation can be carried out either ex-situ (in a chemical plant after mining and preparing the silicate), or in-situ (by injecting CO 2 into silicate-rich geological rock formations). The reaction of the metal oxide with the CO 2 releases heat and therefore the CCUS process produces energy as well as permanently storing/sequestering the CO 2.
There are currently 18 full sized CCS projects in operation, capturing 0.1% of global emissions. Five others are under construction, with 20 more in various stages of development. These are in Canada, the USA, China, the Middle and Far East as well as in Europe.
The first industrial-scale CO 2 storage project in the world was the Sleipner CCS project  offshore Norway. Here, natural gas is produced from a deep sandstone reservoir; CO 2 is extracted and is injected into a shallower sandstone unit at a depth of 800-1000 m. Starting in 1996, to date more than 17 million tonnes have been safely stored in the subsurface. Intensive monitoring (including eight repeated 3D time-lapse seismic surveys during the past 20 years) of the movement and behaviour of the sequestered CO 2 shows no evidence of leakage into the rocks overlying the cap rock, or at the seabed. In addition, no induced seismic activity (earthquakes) can be attributed to the effects of CO 2 injection at Sleipner. Other notable large-scale CCS projects are the Weyburn CCS-EOR project  in Saskatchewan, Canada which has been operating for over a decade, injecting more than 18 million tonnes of CO 2 into a limestone reservoir, and the In Salah project in Algeria where 3.8 million tonnes of CO 2 were injected into a low porosity sandstone over the period 2004-2011, reaching 1.2 million tonnes annually at its peak. Similarly, in Texas, a plant to the value of $150 million has been built by Net Power, a start-up on a journey to create a new type of power plant that will appeal to established energy companies. Despite the cost of building the plant, the running of it is set to be on par with any other plant making it ideally suited to wider adoption. The revolutionary plant can produce 25 megawatts. This is enough to power all the homes in a medium-size town simultaneously. 
The potential of CCS and CCUS
CCS and (CCUS) technologies feature significantly in all comprehensive climate plans. They are mentioned in the IPCC latest (2018) report  which suggests that major reductions in greenhouse gas emissions can be achieved “… through combinations of new and existing technologies and practices, including …. carbon capture, utilization and storage (CCUS)”. An earlier IPCC Special Report on CCS (2005)  stated that ‘‘….the potential of CO 2 capture and storage is considerable, and the costs for mitigating climate change can be decreased compared to strategies where only other climate change mitigation options are considered”.
The 2013 policy report of the European Academies Science Advisory Council (EASAC)  concluded that CCS has the potential to make an important contribution to Europe’s efforts to substantially decarbonise its electricity system and to achieve targets of greenhouse gas reduction. CCS has also been identified in the Irish Government’s Energy White Paper  as a potential bridging technology that could support the transition to a low carbon economy.
It is one of the very few technologies that can reduce large-scale emissions from a broad range of industrial sources including power plants, cement factories, steel work, refineries and petrochemical plants.
However, while proven at scale, what is inhibiting CCS at present is economic rather than technical and thus appropriate policies are required to incentivize CCS. Establishing an effective global carbon pricing scheme would help focus attention on the cost of emissions and encourage CCS and other mitigation initiatives, thereby offering business opportunities as well as helping in the quest to mitigate the emissions.
CCS potential in Ireland
A 2008 report evaluated the potential for CCS in Ireland . This showed significant potential to store CO 2 in geological formations in the offshore, either utilising depleted gas fields or other geological structures. The report suggested that, if proven to capacity, the Kinsale Head gas field, which is expected to be decommissioned in the near future, could store the equivalent of more than 60 years’ of the emissions from the Moneypoint coal-fired power station.
Ervia are currently assessing the feasibility of developing a large-scale CCS project at the Kinsale Head gas field area . Existing local infrastructure could potentially be repurposed; the two relatively modern combined cycle gas turbines in the area may be suitable for post-combustion carbon capture, while the offshore pipeline could potentially be reutilised to carry CO 2 back to reinject into the Kinsale Head subsurface reservoir.
The oil and gas sector can play a critical role in the identification of geological locations as well as the provision of infrastructure and expertise for the development of CCS and CCUS in Ireland.
It will be virtually impossible to get to net zero carbon by 2050 without CCS. It offers very significant potential to major a major contribution to meeting the Paris Agreement targets. The late Samuel Bodman (US Secretary of Energy) commented “If the (CCS) methodology used in the Weyburn Project was successfully applied on a worldwide scale, one-third to one-half of CO 2 emissions could be eliminated in the next 100 years”. CCS, deployed at scale, is a potential climate game-changer.
 Metz, B., Davidson, O., de Coninck, H., Loos, M. and Meyer, L. (eds). 2005. IPCC Special Report on Carbon
Dioxide Capture and Storage. Cambridge University Press. 431 pp. https://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf
 Energy White Paper. 2015. Ireland’s Transition to a Low Carbon Energy Future, 2015-2030. Department of
Communications, Energy and Natural Resources.
 Assessment of the Potential for Geological Storage of CO2 for the Island of Ireland. 2008. Report prepared for
Sustainable Energy Ireland, Environmental Protection Agency, Geological Survey of Northern Ireland,
Geological Survey of Ireland.