CCS – Storing Carbon Dioxide deep in the ground
Carbon capture and storage (CCS) refers in general to the process of capturing CO2 and storing it under the ground. CCS was developed to capture the CO2 emitted by large point sources such as cement works or coal or natural gas power plants before it enters the atmosphere. The CO2 is subsequently injected into deep-lying rock formations or exhausted natural gas or oil deposits. CCS itself is not referred to as climate engineering. However, it is needed as a means of storing CO2 for various proposed CDR methods. Examples include bioenergy with CCS (BECCS) and direct air capture.
About 20 CCS research projects have so far been carried out worldwide to examine how well CCS actually works and the associated risks. In some cases, they have involved building very large CCS pilot plants, some of which have now been in operation for over ten years. An example is the Sleipner project in the Norwegian part of the North Sea, in which CO2 that has to be extracted during natural gas production is injected into the Utsira sandstone formation. The project also examines how well the sandstone formation is suited to permanent storage of CO2. Worldwide, the pore spaces in such sandstone formations offer a large storage reservoir for CO2. The CO2 reacts with the sandstone and is thus chemically neutralised. In addition to that, there is storage space freed by exhausted natural gas and oil deposits. Germany has exhausted natural gas deposits with a storage capacity of some 2.5 billion tonnes and sandstone formations with a capacity of over nine billion tonnes.
In principle, CCS technology has been sufficiently researched and made ready for deployment as a result of research work conducted in recent years. Research projects between 1994 and 2005 initially aimed to evaluate the technology, design projects, and analyse the legal and regulatory systems that might be used to manage CCS in the future. A number of very large pilot plants were then built between 2005 and 2015. To continue operating, however, these rely on subsidies as there are hardly any viable CCS business models to date. So far it has not been possible to finance them from trading emission allowances because the price for emitted CO2 is too low. The only profitable CCS plants are in the USA where the captured CO2 is sold to the oil industry. Oil companies inject the CO2 into near-exhausted deposits in order to recover the remaining gas and oil. Many funding programmes for CCS research worldwide, and especially in the USA, are due to expire in the near future. As there are hardly any new funding programmes on the agenda, it is possible that after 2020 existing CCS projects will have to cease operation and no new research projects will be approved
The International Energy Agency in Paris has determined in scenarios that CCS plants with the capacity for six billion tonnes of CO2 a year would have to be available for BECCS or direct air capture by 2050 in order to achieve the 2 °C target. That would require a large series of new plants to go into operation in the years ahead. If CCS projects are only funded on about the same scale as in previous years, however, CCS plants with a capacity of only around 700 million tonnes will be available by 2050.
In view of the controversy surrounding CCS and storing CO2 in the ground, it seems likely that in many countries, it will only be used if further research is done into the opportunities and risks for each location and public acceptance of the technology can be improved. If CCS research were instead to be further scaled back, that would also rule out the development of expertise in CO2 storage for BECCS and direct air capture. Thorough geological surveys and the selection of suitable storage reservoirs typically take at least ten years and a further five years are needed to evaluate the specific CCS plant and obtain the necessary permits. If research is now halted, that will further postpone the potential starting date for using CCS in combination with BECCS and direct air capture. It would then probably be too late to achieve the targets under the Paris Climate Agreement with the CDR methods proposed so far. A responsible course of action for the international community would be for countries to appraise the potential for future CO2 storage on their territory today in order to keep the option for CCS in combination with BECCS and direct air capture open at a later date. International approaches also need to be developed for practicable incentive, control and governance systems for the storage of CO2. ◆