Background

On the whole, the primary focus of CO₂ storage monitoring techniques has been to monitor plume behaviour in storage formations, and to detect leakage to the biosphere.  However, for emissions trading under the EU ETS and for national GHG inventory purposes it is necessary to quantify leaked emissions to the atmosphere should leakage occur, and there is a low level of understanding of the capabilities, accuracies and uncertainties of measurement techniques for this application.  Quantification of leakage was identified as a significant gap in the knowledge base of the IEAGHG storage networks at the Joint Network Meeting in June 2008, and the IEAGHG Environmental Impacts of Leakage workshop held in September 2008 highlighted potential for quantitative measurements to a level of accuracy required although inconclusive.  Both the EU ETS work on monitoring and reporting guidelines for CCS and the EU CCS Directive working group concluded there is insufficient knowledge in this area; hence, it is pivotal for policy, regulations and for the development of monitoring technologies to ascertain the current state of knowledge in this field and understand possible future developments to meet requirements.

Advanced Resources International (ARI), a company based in the USA was commissioned by IEAGHG to undertake this study.

Conclusions and Recommendations

The study results highlight that for potential leaked emissions in the shallow subsurface, atmosphere and marine environment, monitoring portfolios should be focussed on identified leakage pathways, making use of deep subsurface monitoring technologies to recognise potential pathways.  Alternatively it will be necessary to deploy monitoring technologies with lower resolution and wide spatial coverage to detect any CO₂ seepage before deploying more sensitive measurement techniques for quantification.  To quantify CO₂ flux, no one technology has been identified, and development of an efficient monitoring portfolio will depend on the specific environment. 

The results show technologies suitable for quantification do exist, however these need further field testing and some proposed methods may prove unsuitable for quantification; for example ECM which though a powerful tool is expensive, complex and measurement errors and uncertainties are issues which remain to be solved.  Additionally, the study highlights largest uncertainty ranges for some techniques may exceed that of current requirements, for example in surface water chemistry techniques and ECM, and it is recommended IEAGHG explore this further.  For quantification purposes, further research should focus on defining sensitivities of instrumentation and uncertainty ranges, testing the technologies in a wide range of conditions for both controlled and natural releases of CO₂.  Future research should also provide further insight into variability of baseline CO₂ flux which will be crucial for ascertaining suitability of techniques for specific environments; in addition to further understanding of CO₂ leakage mechanisms including conditions driving CO₂ release into the water column in a dissolved phase or as bubbles.  On-going EU projects should help to build knowledge in this area.  Some areas of the report are weaker than others due to data availability such as technologies in the marine environment; therefore such should be re-examined in future relevant studies.  Therefore, it is recommended IEAGHG keep abreast of the latest developments in monitoring capabilities and uncertainties; with further future involvement in relevant collaborative research activities; and consider a re-evaluation of quantification techniques for CO₂ leakage once further research results become available.

The study also provides a number of technology specific recommendations, provided within the final chapter of the report.  These specific recommendations include a need for further testing specific to CO₂ seeps for surface water chemistry techniques in order to assess method sensitivity, precision and costs for CO₂ monitoring.  There is also a need for further development of long open path lasers with more stable baseline signals and that can measure more than one pathway and, further focus on deploying short open path lasers closer the ground surface to minimise potential anomalies and testing models to monitor tracer gases that have lower sensitivity.  For shallow groundwater monitoring, further research should examine integration of indirect methods such as EM to enable wider spatial coverage and, for airborne EM further work should examine the discrimination of the effects of CO₂ leakage from alternative scenarios such as seawater intrusion.