Carbon capture and storage: how much leakage is acceptable?
Carbon capture and storage (CCS) is expected to play a key role in climate change mitigation strategies. However, identification of safe underground storage sites and the impacts of CO2 leakage are still being addressed. New research has modelled the effects of CO2 leakage and found that leakage rates of just 1 per cent could prevent CCS from being economically and environmentally viable.
CCS could cut emissions from power stations using fossil fuel, such as coal, and it has been suggested that no new power plants should be built without CCS facilities. Storage options include injecting CO2 into aquifers, depleted oil and gas reservoirs and using CO2 for enhanced oil and gas recovery (EOR)2 or enhanced coal bed methane recovery (ECBM).
However, it is possible that CO2 could leak back into the atmosphere, reducing the effectiveness of CCS as an option for mitigating against climate change mitigation.
Using the MARKAL4 model for Western Europe, researchers investigated the impact of CCS and possible leakage of
stored CO2 over a century (2000-2100). The researchers modelled two situations:
- If no climate change policies are implemented fossil fuel use would continue dominate to electricity generation during the century. In this ‘no-climate change policy’ scenario, CCS technologies were predicted to play a small role in power generation due to the benefits of energy recovery, while at the same time offering some mitigation against climate change.
- Implementation of policy that dictates that CO2 concentrations should not exceed 550 ppmv (parts per million by volume) CO2. This required increased use of renewable energy sources but the model also predicts significant use of CCS technologies.
The impact of CO2 leakage at rates of 1 per cent 0.5 per cent, 0.1 per cent and 0.05 per cent was also investigated.
Results indicated that CO2 leakage rate at 1 per cent per year is too high for CCS to be an effective mitigation option.
In this scenario, the use of renewable energy sources or nuclear power would be needed to achieve the necessary
reductions.
However, at a leakage rate of 0.5 per cent per year or below, CCS is an effective option. Leakage level had little impact on the costs of CO2 emissions, which were predicted to remain below 50 Euros per tonne of CO2 until 2060, rising to 150 Euros by 2100. Regardless of leakage level, an annual cost of maintaining atmospheric CO2 concentrations below 550 ppmv is predicted to remain less than 0.5 per cent of the gross domestic product (GDP) over the course of the entire century.
The European Commission is developing a programme of work to ensure that CCS is deployed safely and a directive on the geological storage of CO2 is being drawn up5. This research suggests that if leakage rates do not exceed 0.5 per cent, introducing CCS may delay the need to reduce levels of fossil fuel use by at least half a century, even under strict climate control policies. This should be taken into consideration for both policy development and when testing the integrity of carbon storage facilities. Future research should focus on determining leakage rates of potential storage sites and on understanding the impacts of leakage and the associated risks to the environment and human health.
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