Research into carbon dioxide (CO2) geological storage has been carried out over two decades, as part of studies to evaluate the feasibility of Carbon Dioxide Capture and Storage (CCS). Recently, there has been an increasing focus on potential impacts to surrounding geological formations and particularly, shallow aquifers and associated potable groundwater resources. Potential leakage of CO2 in supercritical and gaseous form from onshore or nearshore deep saline formations (DSF), or of the associated formation brines, is frequently cited as a key risk scenario for the overlying or neighbouring shallower groundwater. To date, the impact of CO2 storage has mainly been studied at near-well and reservoir scale, whereas risks in the context of regional multilayered groundwater systems have not yet been systematically assessed. Recent studies have begun to address this topic, using hydrodynamic and geochemical modelling approaches, and have identified several potential mechanisms that can lead to negative impact on groundwater quantity and/or quality. The IEA Greenhouse Gas R&D Programme (IEAGHG) recently commissioned the CO2GeoNet Association to undertake a literature review and unpublished original work on this topic, with the aim of summarising ‘state of the art’ knowledge and identifying knowledge gaps and research priorities in this field. This paper is a summary of this report
