Quantifying geological CO2 storage security to deliver on climate mitigation

Bryan Lovell Meeting 2019 in London, 21 - 23 January 2019Carbon Capture and Storage (CCS) can help nations meet their Paris CO2 reduction commitments cost-effectively. However, lack of confidence in geologic CO2 storage security remains a barrier to CCS implementation. Leak rates of 0.01% yr-1, equivalent to 99% retention of the stored CO2 after 100 years, are referred to by many stakeholders as adequate to ensure the effectiveness of CO2 storage. Secure storage must allow global average temperature increases, driven by excess CO2, to remain well below 2°C; these timescales are typically modelled to be 10,000 years. Thus, leakage rates must remain below an average linear rate of 0.01% yr-1 for that timespan. Many studies that assess global industry-wide risk of subsurface gas leakage do not specifically consider subsurface CO2 retention mechanisms, despite experimental measurements showing that residual trapping may immobilise a significant proportion of the CO2 almost immediately on injection. The published studies that incorporate subsurface CO2 retention into their risk assessments are for site-specific, real or hypothetical, hydrogeological models, rather than industry-wide, regional, or global scenarios. Here, we present a numerical program that calculates CO2 storage security and leakage to the atmosphere over 10kyr. This links processes of geologically measured CO2 subsurface retention (residual and dissolution trapping), and CO2 leakage estimates (based on measured surface fluxes from appropriate analogues). We model 12 GtCO2 of cumulative storage based on the EU¿s 2050 target, commencing injection in 2020, and calculate CO2 retention for well-regulated onshore and offshore scenarios, and for a hypothetical onshore, poorly regulated scenario. The Storage Security Calculator (SSC) is a tool to simulate the long-term (10kyr) security of CO2 storage at a basin scale. Simulations show that CO2 storage in regions with moderate abandoned well densities and that are regulated using current best practice will retain 96% of the injected CO2 over 10,000 years in more than half of cases, with maximum leakage of 9.6% in fewer than 5% of cases. Poorly unregulated storage is less secure, but over 10,000 years, less than 27% of injected CO2 leaks in half of the simulations; up to 34% leaks in just 5% of cases. This leakage is primarily through undetected and poorly abandoned legacy wells, and could be reduced through effective leak identification and prompt remediation of leakage. Natural subsurface immobilisation means that this leakage will not continue indefinitely. Regulators can most effectively improve CO2 storage security by identifying and monitoring abandoned wells, and perform reactive remediation should they leak. Geological storage of CO2 is a secure, resilient and feasible option for climate mitigation even in overly pessimistic poorly regulated storage scenarios and thus CO2 storage can effectively contribute to meeting the Paris 2015 target