The main objective of this report is to compile and review existing and emerging geotechnical methods for the monitoring of CO2 geological storage. It includes examples of general concepts and site-specific applications. This introductory chapter provides a summary of the general context, conditions and requirements for monitoring of CO2 storage. Monitoring purposes include health, safety and environmental provisions (HSE), quantification of emissions according to the Emission Trading Scheme (ETS), operational and contingency monitoring and information of local citizens. The legal acts and regulations for the various subjects of protection are listed briefly.

The EU Directive on CO2 Geological Storage requires that monitoring plans are to be based on risk assessment. Thus, HSE monitoring must pay special attention to protected subjects and potential pathways for leakage, e.g. spill points, fractures and faults, weak points or gaps in caprocks or (abandoned) wellbores. An overview of the potential impacts of leaking CO2 are given from different perspectives - namely the HSE, ETS and operational perspectives, considering different compartments, e.g. the reservoir, neighbouring aquifers, (abandoned) wellbores and near-surface eco-compartments. In addition to potential impacts by CO2, risk assessment and monitoring need to take into account potential impacts related to associated incidental substances ("impurities"), mobilised substances and displaced fluids. Potential impacts may also include movement and deformation of rocks caused by changes of fluid pressure in the reservoir and surrounding rocks.

A comprehensive monitoring concept considers all monitoring purposes in all spatial compartments and all storage phases. Site-specific monitoring plans have to enable the tracking of the migration of fluids in the subsurface and adapt to the dynamic evolution of a CO2 storage site. Monitoring techniques must provide information on the storage complex performance and on substances and processes of concern. The elements of such a comprehensive monitoring concept are outlined and summarised in an overview table that can be used to check site-specific monitoring plans for completeness.

The main objective of this report is to compile and review existing and emerging geotechnical methods and concepts for an evaluation of the performance of geological CO2 storage sites. The report includes a summary of the general context, conditions and requirements for monitoring, and it provides an overview of proposed general monitoring concepts. General monitoring concepts are useful for the development of comprehensive site-specific monitoring plans and the selection and application of appropriate technical tools to consider all monitoring purposes and address all identified risks. The provisions of the EU CCS Directive and the relevance of other guidelines and regulations in place for procedures to set up site-specific monitoring plans are discussed.

In this report, monitoring techniques are introduced and discussed in the context of specific compartments and/or monitoring purposes, like e.g. monitoring the CO2 plume migration in the storage reservoir, monitoring of faults and abandoned wells or monitoring of separate freshwater aquifers above a CO2 storage reservoir. More detailed information about different monitoring methods can be found in the IEA GHG technical report 2012/2 (IEAGHG, 2012) prepared by members of CO2GeoNet.

The technical descriptions of monitoring methods in this report include examples for specific applications or monitoring tasks and for the evaluation of the performance of geological CO2 storage. They are supplemented with examples of site-specific monitoring applications at demo or pilot CO2 storage projects and test sites.

Two examples for potential future storage sites illustrate the procedure of setting up site-specific monitoring plans, meeting multiple monitoring purposes. These examples were selected to represent the two major storage options in Europe and worldwide namely saline aquifers and depleted gas fields.

The report and its conclusions and recommendations shall stimulate the ongoing dialogue between regulators, operators, researchers and developers of monitoring tools for a long-term, safe CO2 geological storage.


in depth

1.1 General considerations and monitoring framework

In general, monitoring is the systematic collection and analysis of information on the status of objects and processes. ...

1.2 Potential risks

Monitoring of “Health, safety and environment (HSE) risks” is focussed on the Earth’s surface or the shallow subsurface...

1.3 Potential impacts

CO2 and CO2-bearing fluids might have various effects in the deep underground, in drinking-water aquifers, in the shallo...

1.4 Comprehensive monitoring concepts

A comprehensive monitoring concept shall meet the different monitoring purposes (see 1.1.1.) in the spatial dimension, a...