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Journal Article | FZJ-2023-05508 |
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2023
Wiley
[New York]
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Please use a persistent id in citations: doi:10.1029/2023WR034722 doi:10.34734/FZJ-2023-05508
Abstract: Understanding geochemical processes and their impact onmacroscopic transport properties of porous media is essential fordescribing the long-term evolution of various subsurfacesystems. Chemical and thermal gradients promote mineralprecipitation reactions in porous media, resulting in a reductionof porosity and potentially clogging transport pathways ofsolutes. Commonly applied porosity-diffusivity relationships incontinuum-scale reactive transport modelling based on Archie’slaw and extended versions thereof describe the case of cloggingas a final state, setting the effective diffusivity to a negligible lowvalue. However, recent experiments and pore-scale modellinginvestigations demonstrated the limitations of empirical laws inpredicting effective transport properties in response to aprecipitation induced porosity reduction and pore clogging,suggesting a non-negligible inherent diffusivity of newly-formedprecipitates. To verify this hypothesis, we developed amicrofluidic reactor design that combines time-lapse opticalmicroscopy and confocal Raman spectroscopy, providing realtimeinsights into mineral precipitation induced porosity cloggingunder purely diffusive transport conditions, using theprecipitation of celestine (SrSO4) as a model system (Figure 1a).As the pore network became clogged, isotopic tracer diffusionexperiments were conducted and monitored by Ramanspectroscopy to visualize the transport of deuterium through theevolving microporosity of the precipitates, demonstrating thenon-final state of clogging (Figure 1b). The evolution of theporosity-diffusivity relation in response to precipitation reactionsshows an increasingly deviating behavior to Archie’s law. Theapplication of an extended power law improved the descriptionof the evolving porosity-diffusivity relation, but still neglectedpost-clogging features. Currently, we develop microfluidicsetups to answer the question how clogging-related processesdepend on initial pore geometries. The combination ofmicrofluidic experiments and pore-scale modelling opens newpossibilities to identify and validate relevant pore-scaleprocesses, providing data for upscaling approaches and to derivekey relationships for continuum-scale reactive transportsimulations.
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