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Shales are abundant in the earth’s subsurface and play a critical role as natural barriers in geo-environmental applications, such as geologic carbon dioxide storage and nuclear waste disposal. Assessing shale permeability is essential for evaluating their sealing capacity. Traditional pore fluid pressure dissipation experiments often provide only an order of magnitude estimation of permeability if specimen geometry and boundary conditions are not properly considered. In this study, a steady-state method is employed to measure the permeability of Maquoketa Shale from the Illinois Basin and identify the influencing factors. Experimental results indicate an exponential decrease in permeability with increasing effective mean stress, with values on the order of 10−21 m2 (nano Darcy), comparable to other claystones with nanoscale pore structures. Over the span of 2 weeks, the average permeability decreases by half due to time-dependent deformation. Plotting stress-dependent permeability vs. porosity reveals a power law relationship, with a sensitivity exponent of 16 for the tested shale. This high exponent value, typical for tight rock, indicates that even small changes in porosity can significantly affect permeability compared to porous geomaterials. It appears that the time-dependent evolution of permeability can be predicted based on the knowledge of poroviscoelastic parameters and the model that considers coupling between the hydraulic and mechanical behavior of rock.
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Onggi’s permeability to carbon dioxide accelerates kimchi fermentation
Since ancient times, Korean chefs have fermented foods in an onggi, a traditional earthenware vessel. The porous structure of the onggi mimics the loose soil where lactic acid bacteria is naturally found. This permeability has been purported to facilitate the growth of lactic acid bacteria, but the details of the process remain poorly understood. In this combined experimental and theoretical study, we ferment salted napa cabbage in onggi and hermetic glassware and measure the time course of carbon dioxide concentration, which is a signature of fermentation. We present a mathematical model for carbon dioxide generation rate during fermentation using the onggi’s gas permeability as a free parameter. Our model provides a good fit for the data, and we conclude that porous walls help the onggi to ‘exhale’ carbon dioxide, lowering internal levels to those favoured by lactic acid bacteria. The positive pressure inside the onggi and the constant outflow through its walls act as a safety valve for bacteria growth by blocking the entry of external contaminants without mechanical components. We hope this study draws attention to the work of traditional artisans and inspires energy-efficient methods for fermenting and storing food products.
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- Award ID(s):
- 1806833
- PAR ID:
- 10459085
- Date Published:
- Journal Name:
- Journal of The Royal Society Interface
- Volume:
- 20
- Issue:
- 201
- ISSN:
- 1742-5662
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1098/rsif.2023.0034
