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Fluid flow on different scales is of interest for several Earth science disciplines like petrophysics, hydrogeology and volcanology. To parameterize fluid flow in large-scale numerical simulations (e.g. groundwater and volcanic systems), flow properties on the microscale need to be considered. For this purpose experimental and numerical investigations of flow through porous media over a wide range of porosities are necessary. In the present study we sinter glass bead media with various porosities, representing shallow depth crustal sediments. The microstructure, namely effective porosity and effective specific surface, is investigated using image processing. We furthermore determine flow properties like hydraulic tortuosity and permeability using both experimental measurements and numerical simulations. By fitting microstructural and flow properties to porosity, we obtain a modified Kozeny-Carman equation for isotropic low-porosity media, that can be used to simulate permeability in large-scale numerical models. To verify the modified Kozeny-Carman equation we compare it to the numerically computed and experimentally measured permeability values.

The process of dehydration in subduction zones is important for (i) element recycling, (ii) hydration of the mantle wedge, as well as (iii) melting processes related to arc volcanism. Additionally, the release of fluids is also proposed to be related to the origin of deep earthquakes. The transport of fluids from the slab into the mantle requires a sufficiently high permeability. Due to shear deformation in subduction zones a strong foliation will be developed by preferred orientation of serpentinite minerals, which might influence the permeability. Measurements of permeability up to 100 MPa indeed showed that the foliation yields a strong anisotropy in serpentinites. The permeability parallel to the foliation is one order of magnitude higher than in the perpendicular direction.Here we present a method to estimate the fluid flux in serpentinites at mantle conditions combining laboratory experiments, X-ray CT scans and numerical modelling. For this purpose, we performed HP-multi-anvil experiments at temperatures of 500 °C to 700 °C and pressure up to 2.5 GPa. As starting material we used a natural antigorite sample showing a strong foliation. A cylindrical drill core is placed into an MgO sleeve. The MgO is hydrated to brucite at the PT conditions at which serpentine is still stable, i.e. serpentine partially dehydrates and brucite is formed as the released fluid moves into the MgO sleeve. After the experiment the location and proportion of brucite formed allows the preferred fluid flux to be determined. The formation of 5 times less volume per unit area of brucite in the direction perpendicular to the foliation indeed indicates a preferred fluid flow parallel to the preferred orientation.In a second step we employ CT scans to obtain data on the pore space of the samples. Finally, using numerical methods, we determine both the porosity as well as the permeability of the recovered samples. Combined, these methods can be used to obtain a model of fluid flow in subduction zones.

The flow of fluids through porous media such as groundwater flow or magma migration are key processes in geological sciences. Flow is controlled by the permeability of the rock, thus an accurate determination and prediction of its value is of crucial importance. For this reason, permeability has been measured across different scales. As laboratory measurements exhibit a range of limitations, the numerical prediction of permeability at conditions where laboratory experiments struggle has become an important method to complement laboratory approaches. At high resolutions, this prediction becomes computationally very expensive, which makes it crucial to develop methods that maximize accuracy. In recent years, the flow of non-Newtonian fluids through porous media has gained additional importance due to e.g., the use of nanofluids for enhanced oil recovery. Numerical methods to predict fluid flow in these cases are therefore required. Here, we employ the open-source finite difference solver LaMEM to numerically predict the permeability of porous media at low Reynolds numbers for both Newtonian as well as non-Newtonian fluids. We employ a stencil rescaling method to better describe the solid-fluid interface. The accuracy of the code is verified by comparing numerical solutions to analytical ones for a set of simplified model setups. Results show that stencil rescaling significantly increases the accuracy at no additional computational cost. Finally, we use our modeling framework to predict the permeability of a Fontainebleau sandstone, and demonstrate numerical convergence. Results show very good agreement with experimental estimates as well as with previous studies. We also demonstrate the ability of the code to simulate the flow of power law fluids through porous media. As in the Newtonian case, results show good agreement with analytical solutions.