Risk and ranking assessments of the potential geological storage units for CCUS deployment in Portugal

Summary Carbon capture, utilisation and storage (CCUS) is a key technology for the energy transition to reduce the global CO2 emissions, being crucial to mitigate emissions in hard-to-decarbonize sectors in which industrial process emission prevail. Safe storage of CO2 during a project lifetime needs to consider the potential risks of CO2 leakage from reservoirs to overburden geological formations and, ultimately, the migration pathways to the surface. Health, safety and environmental (HSE) assessments must be conducted to better understand the quality of the entire subsurface storage complexes and their suitability to deploy CO2 injection and retain it for long-term periods. This paper presents the results from the application of the HSE Screening and Ranking Framework (SRF) to the ensemble of thirty- six potential storage units located in four sedimentary basins in Portugal. The HSE SRF method enabled to improve the identification and classification of the safer storage units (and clusters) and to discard those that do not present appropriate characteristics to proceed with further detailed characterisation studies. The Lusitanian Basin, with suitable and with lower risk potential reservoirs, is the most promising area in Portugal to conduct the CCUS technology.