Impact of geometrical properties on permeability and fluid phase distribution in porous media

Lehmann, Peter; Berchtold, M.; Ahrenholz, Benjamin; Tölke, Jonas; Kaestner, Anders; Krafczyk, Manfred; Flühler, H.; Künsch, Hans R.

doi:10.1016/j.advwatres.2008.01.019

Cited by 57 publications

(34 citation statements)

References 38 publications

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“…Lehmann et al [125] therefore conclude that the PSD's derived from the capillary pressure/fluid saturation relationship does not correspond to the geometrical PSD. Despite these shortcomings, the capillary tube model is widely applied as a simple link between continuumscale hydraulic properties and PSD's [17,18,29,126].…”

Section: General Model Discussionmentioning

confidence: 99%

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

Wissmeier

Barry

2009

Advances in Water Resources

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT AbsThe selective radius shift model was used to relate changes in mineral volume due to precipitation/dissolution reactions to changes in hydraulic properties affecting flow in porous media. The model accounts for (i) precipitation/dissolution taking place only in the water-filled part of the pore space and further that (ii) the amount of mineral precipitation/dissolution within a pore depends on the local pore volume. The pore bundle concept was used to connect pore-scale changes to macroscopic soil hydraulic properties. Precipitation/dissolution induces changes in the pore radii of water-filled pores and, consequently, in the effective porosity. In a time step of the numerical model, mineral reactions lead to a discontinuous pore-size distribution because only the water-filled pores are affected. The pore-size distribution is converted back to a soil moisture characteristic function to which a new water retention curve is fitted under physically plausible constraints. The model equations were derived for the commonly used van Genuchten/Mualem hydraulic properties. Together with a mixed-form solution of Richards' equation for aqueous phase flow, the model was implemented into the geochemical modelling framework PHREEQC, thereby making available PHREEQC's comprehensive geochemical reactions. Example applications include kinetic halite dissolution and calcite precipitation as a consequence of cation exchange. These applications showed marked changes in the soil's hydraulic properties due to mineral precipitation/dissolution and the dependency of these changes on water contents. The simulations also revealed the strong influence of the degree of saturation on the development of the saturated hydraulic conductivity through its quadratic dependency on the van Genuchten parameter . Furthermore, it was shown that the unsaturated hydraulic conductivity at fixed reduced water content can even r tract increase du ing precipitation due to changes in the pore-size distribution.

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Section: General Model Discussionmentioning

confidence: 99%

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

Wissmeier

Barry

2009

Advances in Water Resources

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“…As best practice, macroscopic properties obtained from computer modeling are often used as validation criteria, whereby the calculated pore structure-related values like porosity (Iassonov et al 2009;Vogel et al 2005), permeability , and capillary pressure curves (Silin et al 2010), are compared to experimental data. Permeability can be derived from Lattice-Boltzmann (LBM) single-phase flow simulations on the segmented images (Chen et al 1991;Coles et al 1998;Ferreol and Rothmann 1995;Lehmann et al 2008;Vogel et al 2005;Zhang and Kwok 2006). Capillary pressure curves can be obtained from quasi-static two-phase flow simulation using a pore morphological approach.…”

Section: Introductionmentioning

confidence: 99%

Fast X-ray Micro-Tomography of Multiphase Flow in Berea Sandstone: A Sensitivity Study on Image Processing

et al. 2014

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Synchrotron-based fast micro-tomography is the method of choice to observe in situ multiphase flow and displacement dynamics on the pore scale. However, the image processing workflow is sensitive to a suite of manually selected parameters which can lead to ambiguous results. In this work, the relationship between porosity and permeability in response to systematically varied gray-scale threshold values was studied for different segmentation approaches on a dataset of Berea sandstone at a voxel length of 3 µm. For validation of the image processing workflow, porosity, permeability, and capillary pressure were compared to laboratory measurements on a larger-sized core plug of the same material. It was found that for global thresholding, minor variations in the visually permissive range lead to large variations in porosity and even larger variations in permeability. The latter is caused by changes in the pore-scale flow paths. Pore throats were found to be open for flow at large thresholds but closed for smaller thresholds. Watershed-based segmentation was found to be significantly more robust to manually chosen input parameters. Permeability and capillary pressure closely match experimental values; for capillary pressure measurements, the plateau of calculated capillary pressure curves was similar to experimental curves. Modeling on structures segmented with hysteresis thresholding was found to overpredict experimental capillary pressure values, while calculated permeability showed reasonable agreement to experimental data. This demonstrates that a good representation of permeability or capillary pressure alone is not a sufficient quality criterion for appropriate segmentation, but the data should be validated with both parameters. However, porosity is the least reliable quality criterion. In the segmented images, always a lower porosity was found compared to experimental values due to micro-porosity below the imaging resolution. As a result, it is recommended to base the validation of image processing workflows on permeability and capillary pressure and not on porosity. Decane-brine distributions from a multiphase flow experiment were modeled in a thus validated µ-CT pore space using a morphological approach which captures only capillary forces. A good overall correspondence was found when comparing (capillary-controlled) equilibrium fluid distributions before and after pore-scale displacement events.

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“…However, this relation requires prior knowledge of the grain density, which might not be available for arbitrary structures. Additionally, other quantities, such as the surface area might influence k [8,9]. In this article we discuss a generalization to arbitrary microstructures and the range of validity close to and far away from the percolation threshold, which is the highest porosity below which there is no sample-spanning conducting phase.…”

Section: Introductionmentioning

confidence: 99%

Direct relations between morphology and transport in Boolean models

et al. 2015

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We study the relation of permeability and morphology for porous structures composed of randomly placed overlapping circular or elliptical grains, so-called Boolean models. Microfluidic experiments and lattice Boltzmann simulations allow us to evaluate a power-law relation between the Euler characteristic of the conducting phase and its permeability. Moreover, this relation is so far only directly applicable to structures composed of overlapping grains where the grain density is known a priori. We develop a generalization to arbitrary structures modeled by Boolean models and characterized by Minkowski functionals. This generalization works well for the permeability of the void phase in systems with overlapping grains, but systematic deviations are found if the grain phase is transporting the fluid. In the latter case our analysis reveals a significant dependence on the spatial discretization of the porous structure, in particular the occurrence of single isolated pixels. To link the results to percolation theory we performed Monte-Carlo simulations of the Euler characteristic of the open cluster, which reveals different regimes of applicability for our permeability-morphology relations close to and far away from the percolation threshold.

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Impact of geometrical properties on permeability and fluid phase distribution in porous media

Cited by 57 publications

References 38 publications

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

Effect of mineral reactions on the hydraulic properties of unsaturated soils: Model development and application

Fast X-ray Micro-Tomography of Multiphase Flow in Berea Sandstone: A Sensitivity Study on Image Processing

Direct relations between morphology and transport in Boolean models

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