Potential CO₂ intrusion in near-surface environments: a review of current research approaches to geochemical processes

Abstract: Carbon dioxide (CO₂) capture and storage (CCS) plays a crucial role in reducing carbon emissions to the atmosphere. However, gas leakage from deep storage reservoirs, which may flow back into near-surface and eventually to the atmosphere, is a major concern associated with this technology. Despite an increase in research focusing on potential CO₂ leakage into deep surface features and aquifers, a significant knowledge gap remains in the geochemical changes associated with near-surface. This study reviews the geochemical processes related to the intrusion of CO₂ into near-surface environments with an emphasis on metal mobilization and discusses about the geochemical research approaches, recent findings, and current knowledge gaps. It is found that the intrusion of CO₂(g) into near-surface likely induces changes in pH, dissolution of minerals, and potential degradation of surrounding environments. The development of adequate geochemical research approaches for assessing CO₂ leakage in near-surface environments, using field studies, laboratory experiments, and/or geochemical modeling combined with isotopic tracers, has promoted extensive surveys of CO₂-induced reactions. However, addressing knowledge gaps in geochemical changes in near-surface environments is fundamental to advance current knowledge on how CO₂ leaks from storage sites and the consequences of this process on soil and water chemistry. For reliable detection and risk management of the potential impact of CO₂ leakage from storage sites on the environmental chemistry, currently available geochemical research approaches should be either combined or used independently (albeit in a manner complementarily to one another), and the results should be jointly interpreted. Graphical abstract: [Figure not available: see fulltext.].