Digital rock physics combines microtomographic imaging with advanced numerical simulations of effective material properties. It is used to complement laboratory investigations with the aim to gain a deeper understanding of relevant physical processes related to transport and effective mechanical properties. We apply digital rock physics to reticulite, a natural mineral with a strong analogy to synthetic open-cell foams. We consider reticulite an end-member for high-porosity materials with a high stiffness and brittleness. For this specific material, hydro-mechanical experiments are very difficult to perform. Reticulite is a pyroclastic rock formed during intense Hawaiian fountaining events. the honeycombed network of bubbles is supported by glassy threads and forms a structure with a porosity of more than 80%. Comparing experimental with numerical results and theoretical estimates, we demonstrate the high potential of in situ characterization with respect to the investigation of effective material properties. We show that a digital rock physics workflow, so far applied to conventional rocks, yields reasonable results for high-porosity rocks and can be adopted for fabricated foam-like materials with similar properties. Numerically determined porosities, effective elastic properties, thermal conductivities and permeabilities of reticulite show a fair agreement to experimental results that required exeptionally high experimental efforts.

<p>Microtomographic imaging techniques and advanced numerical simulations are combined by digital rock physics (DRP) to obtain effective physical material properties. The numerical results are typically used to complement laboratory investigations with the aim to gain a deeper understanding of physical processes related to transport (e.g. permeability and thermal conductivity) and effective elastic properties (e.g. bulk and shear modulus). The present study focuses on DRP and laboratory techniques applied to a rock called reticulite, which is considered as an end-member material with respect to porosity, stiffness and brittleness of the skeleton. Classical laboratory investigations on effective properties, such as ultrasonic transmission measurements and uniaxial deformation experiments, are very difficult to perform on this class of high-porosity and brittle materials.</p><p>Reticulite is a pyroclastic rock formed during intense Hawaiian fountaining events. The open honeycombed network has a porosity of more than 80 % and consists of bubbles that are supported by glassy threads. The natural mineral has a strong analogy to fabricated open-cell foams. By comparing experimental with numerical results and theoretical estimates we demonstrate the potential of digital material methodology with respect to the investigation of porosity, effective elastic properties, thermal conductivity and permeability</p><p>We show that the digital rock physics workflow, previously applied to conventional rock types, yields reasonable results for a high-porosity rock and can be adopted for fabricated foam-like materials. Numerically determined effective properties of reticulite are in good agreement with the experimentally determined results. Depending on the fields of application, numerical methods as well as theoretical estimates can become reasonable alternatives to laboratory methods for high porous foam-like materials.</p>

We applied three oscillatory methods, the previously presented axial pore-pressure and pore-flow methods, and the laboratory application of the radial oscillatory pore-flow method, and performed steady-state flow-through experiments (Darcy tests), for comparison, in experiments on samples of Westerly granite and Wilkeson sandstone. The granite and the sandstone exhibit pore spaces dominated by micro-fractures and by the granular-medium character with a connected porosity of about 1 and 10 %, respectively. Permeability determined by the axial pore-pressure method shows the closest agreement with the results of the Darcy tests. Apparent porosity and drained modulus derived from specific storage capacity deviate from measured connected porosity and reference values, respectively. The observed deviations of the hydraulic properties between methods suggest that they bear information about the structure of the pore space. Only for the sandstone, anisotropy in hydraulic properties appears to contribute to differences between the results of the various methods. We argue that oscillatory testing provides three indicators for heterogeneity, period dependence, the relation between apparent and connected porosity, and the relation between amplitude ratio and apparent penetration depth, calculated from the simple scaling law for homogeneous materials. These indicators consistently classify the samples of Wilkeson sandstone as hydraulically homogeneous and those of Westerly granite as heterogeneous.

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