| Abstrakt: |
Understanding mineral precipitation induced porosity clogging and being able to quantify its non‐linear feedback on transport properties is fundamental for predicting the long‐term evolution of energy‐related subsurface systems. Commonly applied porosity‐diffusivity relations used in numerical simulations on the continuum‐scale predict the case of clogging as a final state. However, recent experiments and pore‐scale modeling investigations suggest dissolution‐recrystallization processes causing a non‐negligible inherent diffusivity of newly formed precipitates. To verify these processes, we present a novel microfluidic reactor design that combines time‐lapse optical microscopy and confocal Raman spectroscopy, providing real‐time insights of mineral precipitation induced porosity clogging under purely diffusive transport conditions. Based on 2D optical images, the effective diffusivity was determined as a function of the evolving porous media, using pore‐scale modeling. At the clogged state, Raman isotopic tracer experiments were conducted to visualize the transport of deuterium through the evolving microporosity of the precipitates, demonstrating the non‐final state of clogging. The evolution of the porosity‐diffusivity relationship in response to precipitation reactions shows a behavior deviating from Archie's law. The application of an extended power law improved the description of the evolving porosity‐diffusivity, but still neglected post‐clogging features. Our innovative combination of microfluidic experiments and pore‐scale modeling opens new possibilities to validate and identify relevant pore‐scale processes, providing data for upscaling approaches to derive key relationships for continuum‐scale reactive transport simulations. Plain Language Summary: Mineral precipitation in porous media alters the pore space geometry and thus affects the transport of fluids and solutes through engineered or geological materials in energy related subsurface systems, used for example, for CO2 sequestration, utilization of geothermal heat, or geological disposal of radioactive wastes. To understand the long‐term evolution of such systems, reactive transport models are employed to simulate transport processes and chemical reactions, coupling changes in porosity and macroscopic transport properties. However, previous studies showed that the effects of localized or widespread pore clogging due to mineral precipitation on diffusive solute transport cannot be captured by the currently used reactive transport models. Here, we conducted microfluidic experiments to resolve the effects of mineral precipitation induced clogging on diffusive solute transport to validate an improved equation coupling porosity and diffusivity (Archie's law). It was shown that an extended version of Archie's law improved the predictability of the transport properties but still neglected reaction processes that occurred after clogging. The combination of microfluidics and pore‐scale modeling provides new possibilities to unravel pore‐scale processes that potentially need to be considered for further improvement of equations used for macroscopic reactive transport simulations. Key Points: Microfluidic experiments to capture precipitation induced porosity clogging under purely diffusive transport conditionsIsotopic tracer experiments for visualization of solute diffusion through the evolving microporosity of the clogging precipitatesValidation of modified Archie's law including critical parameters by effective diffusivities derived from experiments and modeling [ABSTRACT FROM AUTHOR] |
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