Reviewing the implications of unlikely but potential CO2 migration to the surface or shallow subsurface

Overview

CO2 leakage from geological storage is considered unlikely from properly selected sites and the potential impacts small when compared to other anthropogenic and natural stressors. However, it is important to predict and understand potential environmental impacts and risks to human health from a range of leak scenarios in order to undertake appropriate monitoring and mitigation necessary to meet both regulatory and societal expectations.

Migration of CO2 to the surface, subsurface or into potable water reservoirs poses a risk, and although is predicted to be rare and limited in quantity, cannot be excluded completely, especially via abandoned wells, along fault surfaces or via gas chimneys. Very strict interpretation of regulatory requirements may impose very high costs or limit the number and size of storage site unnecessarily, thus potentially reducing the regional and global storage resources severely.

Given the important role that carbon capture and storage (CCS) plays, as a part of negative emission technologies (NETs) and emission reduction technologies, in most climate scenarios (IPCC, IEA and others), a balance between the merits of CCS on a global scale and the potential risks at a local scale, needs to be evaluated. A growing body of knowledge, gleaned over the past two decades into the environmental impact of leaked CO2 have included studying the impact of CO2 release in: natural seings, potable aquifers, via laboratory and controlled release experiments and modelling. It was desirable, therefore, that these learnings were summarised and evaluated in a clear and accessible document that would be of value to policymakers, project developers and regulators.