Mitigation and remediation technologies and practices in case of undesired migration of CO2 from a geological storage unit—Current status

International audienceOne of the main objectives of operators and regulators involved in CO2 geological storage activities is to ensure that the injected CO2 will remain safely in the underground for a long period of time. Therefore, in addition to the screening and evaluation of the performance of a potential CO2 storage site, risks of unwanted migration in the subsurface should be addressed and adequately managed. This can include the use of methods to mitigate those risks and ultimately to remediate potential adverse effects. This paper reviews the status of knowledge with regards to the mitigation and remediation technologies, from mature techniques adapted from other fields, such as oil and gas industry and environmental clean-up, to research topics offering potential new possibilities. Several categories can be defined: (1) interventions on operational or decommissioned wells to re-establish their integrity; (2) pressure/fluid management techniques for countering the leakage driving forces and/or removing the leaking fluids; (3) emerging technologies providing new mitigation opportunities for controlling undesired CO2 migration; (4) techniques to remediate the impacts potentially induced by such a migration. This technical state of the art is completed by the actual practices in the emerging field of CO2 geological storage established from the regulatory requirements and guidelines, and from the experience gained in existing storage projects over the world. This article concludes on important best practices stemming from this review and on future challenges in terms of research topics and operational needs

Potential impacts on groundwater resources of deep CO2 storage

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