3.6 Conclusions

The main purpose of CCS technology is to prevent any further emissions of CO2 to the atmosphere from fossil fuel based energy production and other industrial processes which produce CO2. Leakage prevention is therefore essential in order to fulfil the purpose of the technology, in addition to avoiding any of the known negative effects to the environment and human health. It is therefore of exceptional importance that all risks relating to leakage of CO2 are considered and accounted for during a storage project, starting at the very beginning, during the site selection stage. Leakage of CO2 at a storage site could occur from the storage reservoir through migration pathways that pass through the overlying bedrock to the surface. These pathways may be natural (e.g. fractures) or anthropogenic (e.g. wells or mining infrastructure). Anthropogenic pathways such as artificial fractures created through hydraulic fracturing during the extraction of minerals and hydrocarbons may be a potential interest of conflict with geological storage of CO2 where they affect cap rock properties.

Regulatory regimes like OSPAR and the EU CCS Directive clearly state the importance of risk analysis and risk management during a storage project in order to decrease the risk of leakage and therefore its effects on human health and the environment. Since the geological conditions of each potential storage site are site-specific, the laws and international agreements have to take this into account. The characterisation of the storage complex and monitoring the behaviour of the injected CO2 are two mandatory operations in a CO2 storage project and are regulated both by OSPAR and the EU CCS Directive. Together they require accumulation of knowledge that can be used to detect leakage from the storage site and enable the appropriate remediation measures to be undertaken in order to prevent leakage or to decrease the effects of leakage.

The composition of the CO2 stream is also regulated. The composition of the CO2 stream will determine the effects of leakage from a storage site since the expected chemical and physical reactions within a storage site are dependent on the composition of the injected CO2 stream and the properties of the hosting rock. The effects of impurities in the CO2 stream on potential leakage pathways are yet not fully understood and the risk of enhancing or causing leakage pathways is most likely dependent on the composition of the injected CO2 stream and the surrounding bedrock.

Local laws and regulations will affect activities at and requirements for the storage site. The EU CCS Directive is transposed by the member states with some slight variations in detail (where it has been fully implemented). Other local planning, health and safety and environmental laws and regulations will also affect the storage site activities. In addition, conflicts of interest and their consequences should always be considered in terms of the physical planning and regulatory regimes of each country.