ECR International Exchange fund still generating impact

New papers published by UKCCSRC member Jen Roberts show UKCCSRC ECR funding can deliver long lasting impact.

Jen Roberts was a recipient of the UKCCSRC Early Career Researcher International Exchange Fund in 2015 which enabled her to do a 10 week research trip to Australia.

She has since returned to Australia with further UKCCSRC support and still continues to collaborate with Dr Linda Stalker and her team. The two papers below are the two most recent publications from this collaboration.

Structural controls on the location and distribution of CO₂ emission at a natural CO₂ spring in Daylesford, Australia

Abstract

Secure storage of CO₂ is imperative for carbon capture and storage technology, and relies on a thorough understanding of the mechanisms of CO₂ retention and leakage. Observations at CO₂ seeps around the world find that geological structures at a local and regional scale control the location, distribution and style of CO₂ emission. Bedrock-hosted natural CO₂ seepage is found in the Daylesford region in Victoria, Australia, where many natural springs contain high concentrations of dissolved CO₂. Within a few meters of the natural Tipperary Mineral Spring, small CO₂ bubble streams are emitted from bedrock into an ephemeral creek. We examine the relationship between structures in the exposed adjacent outcropping rocks and characteristics of CO₂ gas leakage in the stream, including CO₂ flux and the distribution of gas emissions. We find that degassing is clustered within ˜1 m of a shale-sandstone geological contact. CO₂ emission points are localised along bedding and fracture planes, and concentrated where these features intersect. The bubble streams were intermittent, which posed difficulties in quantifying total emitted CO₂. Counterintuitively, the number of bubble streams and CO₂ flux was greatest from shale dominated rather than the sandstone dominated features, which forms the regional aquifer. Shallow processes must be increasing the shale permeability, thus influencing the CO₂ flow pathway and emission locations. CO₂ seepage is not limited to the pool; leakage was detected in subaerial rock exposures, at the intersection of bedding and orthogonal fractures.

These insights show the range of spatial scales of the geological features that control CO₂ flow. Microscale features and near surface processes can have significant effect on the style and location and rates of CO₂ leakage. The intermittency of the bubble streams highlights challenges around characterising and monitoring CO₂ stores where seepage is spatially and temporally variable. CCS monitoring programmes must therefore be informed by understanding of shallow crustal processes and not simply the processes and pathways governing CO₂ fluid flow at depth. Understanding how the CO₂ fluids leaked by deep pathways might be affected by shallow processes will inform the design of appropriate monitoring tools and monitoring locations.

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An experimental investigation into quantifying CO₂ leakage in aqueous environments using chemical tracers

Abstract

Chemical tracers can be an effective means of detecting, attributing and quantifying any leaks to the surface from geological CO₂ stores. CO₂ release experiments have found it difficult to ascertain the fate, or quantify the volume of CO₂ without the application of tracers. However, a significant proportion of global CO₂ storage capacity is located offshore, and the marine environment poses constraints that could limit the success of using tracers. These constraints include uncertainties in the behaviour of tracers in marine sediments and the water column and samplingchallenges. However, to date there have been few experimental investigations to address these uncertainties. Here, we used a benchtop experimental setup to explore how effectively methane, a common constituent of captured CO₂ and of reservoir fluids, can aid the quantitation of CO₂ leakage in aqueous environments. The experiment simulated gas leakage into sediments that mimic the seabed, and we measured the partitioning of co-released gases under different environmental conditions and injection rates. We find that the style of seepage and the fate of the CO₂ are affected by the presence of a sand layer and the injection rate. We discuss the implications for leak monitoring approaches, including how tracers may be used to quantify the leak rates and fate of CO₂ in aqueous environments. Our work contributes to ongoing efforts to develop robust offshore monitoring system that will assure operators, regulatory bodies and the public of CO₂ storage integrity.

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