Improving monitoring protocols for CO2 geological storage with technical advances in CO2 attribution monitoring
Introduction
Greenhouse gas (GHG) accounting is an important method for showing compliance to emissions commitments made under binding protocols (i.e., Kyoto Protocol), for documenting credits from GHG mitigation efforts in areas where greenhouse gases are regulated, and for planning and implementing low-carbon growth in developing countries. With the realization that carbon dioxide capture and geologic storage (CCS) will be required to provide up to 20% of the emissions reductions needed to achieve climate change mitigation goals (IEA, 2015), CCS has been increasingly included in global climate regulations and protocols. GHG accounting at geologic sites where captured CO2 is stored is not as straightforward as for other emissions reduction technologies. The complexity lies in the slight but possible chance that small amounts of CO2 stored deep in a geologic formation could, over time and with the right conditions, migrate upward to ground surface and eventually be released to atmosphere. In this case, leakage would need to be located within a large ‘area of review’ (AOR) and then quantified for accounting purposes.
The first step in monitoring for leakage emissions is to identify or detect a signal or anomaly that could potentially represent leakage. The second step is to assess the origin of that anomaly. CO2 exists naturally in the near-surface and its concentration varies in space and time with fluctuating environmental conditions; therefore discriminating leaked CO2 from naturally-occurring CO2 is important and can be challenging. This discrimination or ‘attribution’ also represents a critical decision point which either leads to no action (in the case of a non-CCS-related origin) or to intensified actions which can include environmental monitoring, quantification for GHG accounting, and possibly remediation.
Since the first protocols for monitoring at geologic CO2 storage sites were written, important advances have been made in leakage detection and attribution in the near-surface (defined by IPCC (2006) as regions less than 10 m below or above the ground surface in terrestrial environments) and important knowledge has been gained through project experience. For example, the importance of this monitoring step was illustrated in 2011 when a landowner claimed leakage from the IEAGHG Weyburn–Midale CO2 Monitoring and Storage Project (WMP) in Saskatchewan, Canada. The leakage claim arose when soil-gas CO2 at the farm was wrongly attributed as leakage. The leakage claim was subsequently disproven by CCS professionals using the latest techniques in attribution. The experience illustrates several important points:
- 1)
Attribution is an important step that represents a critical decision point in monitoring. If leakage is verified, a range of intensive activities will ensue; thus making attribution important to monitoring.
- 2)
Attribution is not necessarily straightforward and must be done with great care using the latest methods and techniques.
- 3)
Accurate and cost-effective methods for attribution now exist and have been tested in an operational setting.
- 4)
CCS guidance documents should reflect both the importance of attribution and the latest technical advances in attribution.
Whereas attribution is not a new concept in CCS, most protocols for monitoring geologic CO2 storage sites are not clear about the need to attribute the source of anomalous CO2 that might be detected in the near-surface. As currently written, some regulations require quantification to begin before attribution. A strong and clear statement on the importance of attribution within these protocols is necessary to avoid costly quantification monitoring unless it is truly warranted by leakage. While many regulation frameworks do not exclude attribution techniques, many regulations also do not include the concept of attribution. Some that do include attribution suggest using methods that are now technically outdated.
This paper synthesizes the pertinent monitoring requirements at geologic CO2 storage sites within current CCS-specific protocols and also reviews the latest proven techniques for attributing CO2 at these sites based on their successful use at the WMP. Suggestions for updating protocols, guidelines and technical guidance documents in light of these technical advances are given with the aim of increasing accuracy and potentially decreasing the complexity and cost of implementing CCS on the scales required for significant emissions reduction.
Section snippets
Background on monitoring protocols for geologic CO2 storage
Monitoring protocols for geologic CO2 storage are provided in all the CCS-specific regulations that have been developed over the last ten years. The main regulations that were developed for geologic CO2 storage are selected here and their relevant monitoring protocols described and then synthesized.1
Attribution technical approach: baseline and beyond
As CCS monitoring protocols call for updates based on technical advances, we now present a discussion of some of the most recent and significant advances in attribution technology which we believe provide an increased level of confidence to support adding an attribution step to CCS monitoring protocols. This discussion may also help to guide the technical scope of attribution protocols moving forward. We continue our discussion using the IPCC definition of the ‘near-surface’ as regions less
Monitoring protocol improvement
These developments in new monitoring techniques and understanding of near-surface processes, and advances in our understanding of the application of existing techniques to CO2 geological storage sites, taken together provide a growing armory of techniques which give confidence that we can identify the source of CO2 detected at the surface or near-surface with greater accuracy and less effort than before. Because we can do this, it would be possible to add a new stage in the generic leakage
Conclusions
This paper describes how new leakage monitoring techniques could be used to improve the existing monitoring protocols for geologic CO2 storage by including a stage of ‘attribution monitoring’ and thereby reducing the need for extensive quantification monitoring before leakage is confirmed. This option of improvement is made possible because of recent developments in monitoring techniques as shown and discussed in recent IEAGHG Network meetings which place new technical advances in monitoring
Acknowledgements
Partial funding for this paper was provided by the Career-Development Publications Award of the Bureau of Economic Geology. The authors wish to thank the members of the IEAGHG Research Networks, and the sponsors of the Gulf Coast Carbon Center at the University of Texas at Austin, USA. The authors also thank the anonymous reviewers for their time and attention toward improving the quality of the manuscript. Publication authorized by the Director, Bureau of Economic Geology.
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2021, GeothermicsCitation Excerpt :The process-based approach seems to provide more effective results in relation to attribution where there is a clear signal, but the source is uncertain. As such, it is a useful tool in relation to CO2 storage, where Dixon and Romanak (2015) assert anomalous gas should be attributed to a leakage before quantification and reporting. In some circumstances a background gas survey is required before subsurface work can commence, however, it seems valuable and prudent to perform a background gas study in novel situations or where there is likely to be a complex history of land use.