Recent advances in microanalytical imaging and machine learning enable quantitative, multiscale characterization of geological materials with direct relevance for subsurface energy storage. This study presents an integrated workflow combining Broad Ion Beam (BIB) sample preparation, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and advanced machine learning to quantify pore structures, mineralogy, and their spatial relationships from the micrometre to nanometre scale (Klaver et al. 2021).High-resolution secondary electron (SE2) and backscattered electron (BSE) imaging, complemented by low-resolution EDX data, provides multimodal datasets for automated analysis. Pore networks are segmented using a pre-trained U-Net deep learning model, enabling efficient and accurate porosity quantification. Mineralogical phases are identified and quantified through a semi-automatic, decision-tree–based segmentation approach. The alignment of SE2 and BSE datasets allows porosity to be directly correlated with specific mineral phases, establishing a robust link between microstructure, mineral composition, and petrophysical properties (Jiang et al, 2021).The applicability of this technology-driven approach is demonstrated through two case studies. Case study 1 investigates geological hydrogen storage in underground salt caverns, focusing on the impact of biotic and abiotic reactions on anhydrite. Flow-cell experiments combined with cryogenic BIB-SEM analyses enable early detection of microstructural, mineralogical, and pore-space changes induced by hydrogen, hydrogen sulfide, and microbial sulfate reduction. Despite slow reaction kinetics, microstructural observations reveal the substantial onset of chemical alteration, biofilm formation, and evolving pore connectivity at the submicron scale, providing essential constraints for geochemical and hydraulic models (Berest et al., 2024).Case study 2 examines fault sealing in mechanically layered limestone–marl successions. Oriented transfer samples from normal fault systems were analysed using multiscale microanalytical workflows to capture marl smearing, mechanical mixing, fracturing, and cementation processes. High-quality microstructural datasets serve as ground truth for training machine learning algorithms for efficient interpretation of 2D image data. The results show that fault cores are composed of recurrent structural building blocks whose distribution and sealing capacity are strongly controlled by the presence and properties of marly interbeds (Schmatz et al., 2022).Overall, the integrated microscopy–machine learning framework provides a transferable, data-driven approach for quantifying coupled structural, hydraulic, and geochemical processes in complex geological systems.ReferencesBerest et al.,2024. Risk assessment of hydrogen storage in a conglomerate of salt caverns in the Netherlands. KEM-28 report. https://www.kemprogramma.nl/documenten/2024/04/03/kem-28-project-rapportfinal-report-kem-28-h2c3-240403_v2Jiang et al., 2021.Workflow for high-resolution phase segmentation of cement clinker from combined BSE image and EDX spectral data. Journal of Microscopy, 1-7.Klaver et al., 2021. Automated carbonate reservoir pore and fracture classification by multiscale imaging and deep learning. 82nd EAGE Annual Conference & Exhibition, Oct 2021, Volume 2021, p.1 – 5.Schmatz et al., 2022. Prediction of Fault Rock Permeability With Deep Learning: Training Data from Transfer Samples of Fault Cores. 83rd EAGE Annual Conference & Exhibition, Jun 2022, Volume 2022, p.1 – 5.

Janos Urai's contributions have significantly enhanced our understanding of salt deformation, particularly in predicting the long-term evolution of solution-mined caverns and radioactive-waste repositories in salt formations. His work delved into phenomena such as the weakening of rock salt by water during long-term creep at low differential stresses. Unlike most laboratory measurements, which are at higher differential stress, Urai's research considers dislocation creep and pressure solution (dissolution-precipitation creep), processes not commonly included in current engineering predictions.Microstructural observations on Zechstein 2 (Z2) rock salt cores in the northern Netherlands reveal substantial grain-size-dependent differences in rock salt rheology. The study compares undeformed salt layers with strongly deformed diapiric ones, showcasing variations in megacrystals and fine-grained halite microstructures that point to different microphysical processes. The microstructural analysis, including optical microscopy of gamma-irradiated thin sections, recrystallized grain-size measurements, electron microscopy, and subgrain-size piezometry, indicates differential stresses between 0.5 and 2 MPa during deformation.The findings highlight the importance of pressure solution creep at low differential stresses, demonstrating its significant impact on strain rate in rock salt. Integrating these results into constitutive flow laws reveals a four-order-of-magnitude difference in strain rates between halite types, emphasizing the role of different dominant deformation mechanisms. The study suggests that incorporating pressure solution creep and microstructural analysis can substantially enhance engineering and tectonic models of rock salt deformation in low-stress conditions.

Two main goals for the industrial, slurry‐based electrode processing are a high process speed and the maximum possible material efficiency. This makes an increased drying rate and active material share favorable, but both are limited by adverse effects on the electrode quality. The adverse effects of fast drying are associated with the migration of binder. In this article, the slurry properties of water‐based graphite slurries are manipulated using a synthetic, layered silicate as additive. The influence of the polymer‐particle composite network on the viscosity, adhesion strength, and cell performance is investigated. By addition of a small amount of additive (0.5 wt% of the dry electrode), the binder migration is mitigated up to a drying rate of 6 g m−2 s−1 for graphite anodes with ≈4.2 mAh cm−2 (corresponding with 30 s drying time) leading to a possible increase of eight times the process speed compared to drying with 0.75 g m−2 s−1 if adverse effects on the tortuosity of the electrodes can be solved. In this work, a combination of additive usage is pointed out with a multilayer approach and first insights are provided in how the binder migration may be mitigated to gain structurally optimized fast‐dried electrodes without losses in electrode quality.

Many methods have been proposed to analyse SEM-EDS hypermaps of hydrated cementitious materials but none can fit all purposes. In this presentation, we review existing methods for phase identification, stoichiometry quantification, and microstructure quantification in cementitious materials and related materials. We first discuss the unique contribution of SEM-EDS with respect to the outstanding scientific challenges towards sustainable construction materials. We then compare the SEM-EDS and image analysis techniques which contribute to answering these challenges. Convergence and divergence in current methods and workflows, and knowledge gaps are highlighted in terms of the specificities of the material (phase assemblage complexity, grain sizes, mixtures, etc.). The discussion is weighted by the required expert knowledge for the sample preparation, microscope operation, and data analysis. We conclude by discussing how microscopy and image analysis integrate into the overall experimental toolkit to investigate and improve cementitious materials.

Microscopic petrographic analysis of fine-grained sediments requires standardised, high-quality preparation of polished sections, generally conducted by water-involved grinding and polishing techniques following respective norms (ISO 7404-2, 2009; ASTM, 2021). However, vitrinite reflectance results show significant variations between different laboratories, partly caused by inconsistencies in sample preparation or poor sample preparation, e.g. due to the effect of swelling clays. This study evaluates the effect of alternative preparation techniques on the reliability and consistency of vitrinite reflectance data measured on shales containing dispersed organic matter (kerogen type III) using (1) an oil-based lubricant for traditional grinding and polishing and (2) BIB (broad-ionbeam) polishing. Different preparation techniques were applied on ten samples from two well sections (Hervest 5 and Prosper-Haniel) from the Ruhr Basin (Germany), covering the coal-bearing Pennsylvanian sedimentary successions of the Westphalian B and C with a maturity range of 0.56 to 0.78% and 0.73 to 0.92% vitrinite reflectance, followed by vitrinite reflectance measurements. Preparation under the use of oil-based lubricant led to similar reflectance values compared to traditional water-based grinding and polishing. Oil-based treatment improved the quality of two samples having the lowest thermal maturities, as indicated by increased vitrinite reflectance values by up to 0.1%. After BIB polishing, vitrinite reflectance systematically increased by up to 0.25% (relative increase of +29%), with the highest BIBinduced reflectance increase observed at a thermal maturity of 0.86% vitrinite reflectance (before BIB polishing). A practical geological approach was tested by calibrating 1D basin models using post-BIB vitrinite reflectance values. The data reveal a systematic trend in vitrinite reflectance between pre- and post-BIB polishing, suggesting that BIB-polishing might has future potential to be established as a routine for sample preparation for microscopic observation of organic material.

Training data is the backbone of developing either Machine Learning (ML) models or specific deep learning algorithms. The paucity of well-labeled training image data has significantly impeded the applications of ML-based approaches, especially the development of novel Deep Learning (DL) methods like Convolutional Neural Networks (CNNs) in mineral thin section images identification. However, image annotation, especially pixel-wise annotation is always a costly process. Manually creating dense semantic labels for rock thin section images has been long considered as an unprecedented challenge in view of the ubiquitous variety and complexity of minerals in thin sections. To speed up the annotation, we propose a human-computer collaborative pipeline in which superpixel segmentation is used as a boundary extractor to avoid hand delineation of instances boundaries. The pipeline consists of two steps: superpixel segmentation using MultiSLIC, and superpixel labeling through a specific-designed tool. We use a cutting-edge methodology Virtual Petroscopy (ViP) for automatic image acquisition. Bentheimer sandstone sample is used to conduct performance testing of the pipeline. Three standard error metrics are used to evaluate the performance of MultiSLIC. The result indicates that MultiSLIC is able to extract compact superpixels with satisfying boundary adherence given multiple input images. According to our test results, large and complex thin section images with pixel-wisely accurate labels can be annotated with the labeling tool more efficiently than in a conventional, purely manual work, and generate data of high quality.

Micro-plugs of the Upper Devonian to Lower Mississippian Woodford Shale from the Ardmore Basin in southern Oklahoma were analyzed before and after hydrous pyrolysis (300, 320, 330, and 340 degrees C for 24 h) by using a combination of It-FTIR, CP-Py-GC/MS, BIB-SEM-EDS techniques to investigate kerogen transformation and evolution of pore space.Tasmanites and Leiosphaeridia in Woodford Shale are abundant macerals characterized by relatively long, unbranched alkyl chains, with an additional carboxyl component, and a minor contribution of aromatic structures based on It-FTIR spectra results. The aliphatic vasCH2/ vasCH3 ratios show almost no correlation with pyrolysis temperatures, except for a minor increase of the ratio for both samples after pyrolysis at 330 degrees C, which may be attributed to cracking of C-C bonds next to a tertiary carbon atom. A decreasing aliphaticity and increasing aromaticity for alginite with increasing pyrolysis temperature and thus thermal maturity is indicated by the reduction of aliphatic CHx stretching bands and increasing gamma CH/ vCHx ratios. The relative abundance of olefinic bonding (vC=C) decreases in alginite compared to aromatic hydrogen (gamma CH) with higher pyrolysis temperature, and thus formation of monoaromatic rings is indicated by the condensation ratios (gamma CH/ vC=C); similar observations have been made on natural maturation series. This is in line with the CP-Py-GC/MS results on whole kerogen showing an increase of aromatic structures over aliphatic pyrolysis products with increasing thermal maturities, though with some differences between the two samples investigated. The differences are probably related to higher alginite/bituminite ratios in one of the samples, which also contain more N-compounds. In contrast, the other sample enriched in bituminite contains more S-compounds. Both FTIR spectra and EDS results document a loss of carbonyl/carboxyl C=O functional groups and/or O content with thermal maturation. The hydrocarbon generation potential parameter "A-Factor" (vCHx/ vCHx + vC=C), analyzed on alginite in this study, is rather consistent at different pyrolysis temperatures with a value of about 0.9 and with a slight tendency of higher values at higher pyrolysis temperatures. SEM observations show that there is no significant occurrence of microfractures in the initial samples and after pyrolysis at 300 degrees C, while microcracks and organic pores formed pore networks when pyrolysis temperature increased from 320 degrees C to 340 degrees C. Most of the newly generated cracks are parallel to the bedding. Mineral-filled Tasmanites cysts in Woodford Shale are silica-rich and may be related to the dissolution of siliceous tests (e.g., radiolarians).

. Constitutive laws of rock salt are required for the prediction of long-term deformation of radioactive waste repositories and solution mined caverns, which are used for energy storage and play an important role in the energy transition. Much of this deformation is at differential stresses of a few MPa. The vast majority of laboratory measurements of 15 salt creep are at much higher differential stress and require extrapolation over many orders of magnitude. This extrapolation can be made more reliable by including microphysical information on the deformation mechanisms in the laboratory samples, integrated with microstructural analysis of samples deformed in natural laboratories at low differential stress. Rock salt can deform at widely different rates at the same temperature and deviatoric stress, depending on state variables such as grain size, solid solution- and second phase- impurities, crystallographic preferred orientation, water content and 20 grain boundary structure. Both dislocation creep and dissolution-precipitation creep processes are common, but dissolution-precipitation creep (pressure solution) is not commonly included in current engineering predictions. Here we show evidence for large grain size-dependent differences in halite rheology based on microstructural observations from Zechstein rock salt cores of the Northern Netherlands that experienced different degrees of tectonic deformation. We studied the relatively undeformed Z2 (Stassfurt Formation)‚ horizontal-layered salt from Barradeel, and compare it with 25 much stronger deformed equivalent in diapiric salt form Winschoten, Zuidwending, and Pieterburen. We used optical microscopy of Gamma-irradiated thin sections for microtectonic analysis, recrystallized grain size measurements and subgrain size piezometry, SEM-EDX and XRD for second phase mineralogy. Subgrain size piezometry shows that this deformation took place at differential stress between 0.5 and 2 MPa, providing a natural laboratory. In the undeformed, layered salt from Barradeel we find cm-thick layers of single crystalline halite (Kristalllagen) alternating 30 with fine-grained halite and thin anhydrite layers. The domal salt samples are typical of the well-known "Kristallbrocken" salt, and consist of cm-size tectonically disrupted megacrystals surrounded by fine-grained halite with grain size of a few mm. We infer high strains in the fine-grained halite as shown by folding and boudinage of thin anhydrite layers, as compared to the megacrystals, which are internally much less deformed and develop subgrains during dislocation creep. Subgrain size shows comparable differential stresses in Kristallbrocken than in matrix salt. The fine-grained matrix salt is dynamically 35 recrystallized, has few subgrains and microstructures indicating deformation by solution-precipitation processes. We infer that the finer grained halite deformed dominantly via pressure solution and the megacrystals dominantly by dislocation creep. This provides evidence that the fine-grained matrix salt is much weaker than Kristallbrocken because of different dominant deformation mechanisms. This is in agreement with microphysical models of pressure solution creep in which grain size has 40 a significant effect on strain rate at these low differential stress. Our results on the operation of pressure solution creep in rock salt at differential stress of a few MPa point to the importance of this mechanism at low differential stresses around engineered structures but also in most salt tectonic settings. We suggest that including results of microstructural analysis can strongly improve engineering models of rock salt deformation. We recommend that this mechanism of grain size dependent rheology is included more consistently in the constitutive laws 45 describing deformation of engineered structures in rock salt.

As normal faults accumulate displacement, smearing of weaker fine-grained materials, such as clays, along their fault plane can reduce fault permeability and thus affect fluid flow in subsurface reservoirs, making clay smear development relevant for groundwater, geothermal and CO2 storage applications. Here we use analogue experiments to investigate the potential of smearing of weaker layers along fault planes in a multi-layer sequence of granular materials.The natural prototype is the interbedded limestone and marl sedimentary units of the Malm formation in a quarry in southern Germany. The normal faults in the quarry have small offset (usually < 50 cm) and dip between 40° – 65° predominantly trending NE – SW. We observe discontinuous marl smearing along the fault planes, which are surrounded by deformation zones with a dense tensile fracture population. Average limestone and marl bed thicknesses on both footwall and hanging wall is 32 cm and 4.5 cm, and 33 cm and 2.5 cm respectively.Our analogue experiments are scaled to represent layers at quarry scale. We tested several sand and gypsum plaster mixtures using empirical and ring shear methods to find cohesive strength contrasts suitable for simulating the limestone-marl sequences. The material tests show that with increasing plaster content and confining pressure, cohesion increases, while the angle of internal friction shows a non-linear behaviour for plaster/sand mixtures. We here use sand for marl layers and gypsum for limestone. We sieve the materials in a 50 x 30 cm box of which half the base plate can drop down along a prescribed angle. We analyse deformation from 2D-timelapse and 3D-CT image data, using PIV and image analysis.Models with sand (marl) layers within gypsum (limestone) without overburden show numerous mode I fractures at the free surface with localized fault planes. Shear zones are steep with dip angles in the range of 66° - 84°. Models with overburden form shear zones with dips ranging from 65° - 83°, forming less mode I fractures, but instead mainly shear fractures that cut across each cohesive layer. Sand smearing is observed to vary in models without overburden, while it is a consistent component of the fault zones at depth in models with overburden. We find that the quantity of sand smear is a function of the thickness of the embedded sand layers. The sand pours into large openings formed between cohesive gypsum powders with simultaneous mixing of the materials during fault displacement. This process causes an accumulation of sheared granular materials along the fault zone and in turn expands the shear zone width.The experiments with overburden show steep dipping fragmented fault zones, as well as the formation of tensile fractures that form in, and cut through cohesive beds, similar to what is observed in the quarry. Sand smearing processes of rolling and mixing in dilatant portions during displacement is however more brittle in nature than ductile smearing observed in the quarry.

Tight carbonate rocks are important hydrocarbon and potential geothermal reservoirs, for example, in CO 2 -Enhanced Geothermal Systems. We report a study of outcrop samples of tectonically undeformed tight carbonates from the upper Jurassic “Malm ß” formation in Southern Germany near the town of Simmelsdorf (38 km NE of Nuremberg) to understand bulk petrophysical properties in relation to microstructure and to compare models for permeability prediction in these samples. We applied Archimedes isopropanol immersion, Helium pycnometry, mercury injection, gamma density core logging, and gas permeability measurements, combined with microstructural investigations and liquid metal injection (LMI-BIB-SEM). In addition, ultrasonic velocity was measured to allow geomechanical comparison of stratigraphically equivalent rocks in the South German Molasse Basin (SGMB). Results show only small variations, showing that the formation is rather homogeneous with bulk porosities below 5% and argon permeabilities around 1.4E−17 m 2 . The presence of stylolites in some of the samples has neither a significant effect on porosity nor permeability. Pores are of submicron size with pore throats around 10 nm and connected as shown by Mercury injection and Liquid Metal injection. Samples have high dynamic Young’s Modulus of 73 ± 5 GPa as expected for lithified and diagenetically overmature limestones. Moreover, no trends in properties were observable toward the faults at meter scale, suggesting that faulting was post-diagenetic and that the matrix permeabilities were too low for intensive post-diagenetic fluid–rock interaction. Petrophysical properties are very close to those measured in the SGMB, illustrating the widespread homogeneity of these rocks and justifying the quarry as a reasonable reservoir analog. Permeability prediction models, such as the percolation theory-based Katz-Thompson Model, Poiseuille-based models, like the Winland, the Dastidar, the capillary tube, and the Kozeny-Carman Models, as well as several empirical models, namely, the Bohnsack, the Saki, and the GPPT Models, were applied. It is shown that the capillary tube Model and the Saki Model are best suited for permeability predictions from BIB-SEM and mercury injection capillary pressure results, respectively, providing a method to estimate permeability in the subsurface from drill cuttings. Matrix permeability is primarily controlled by the pore (throat) diameters rather than by the effective porosity.

The KEM-17 project of the Dutch State Supervision of Mines presented a critical review of concepts of cavern abandonment and related science. It recommended that analyses of cavern abandonment are done as an integrated project, addressing (i) micro-scale physical processes, (ii) cavern scale models based on field scale experiments and numerical models, (iii) the salt dome scale, to model the far field of the salt caverns. The Cavern Closure Consortium (CCC) project is based on this, focusing on the Haaksbergen and Heiligerlee cavern fields in the Netherlands. We build on (i) innovative deformation experiments, integrated with state of the art microstructural analysis to define constitutive equations for deformation and permeation, focusing on the poorly understood domain below 8 MPa differential stress, (ii) numerical finite element models of the cavern field combined with cavern-scale field experiments to define the closure parameters and temperature evolution of the cavern, and (iii) state of the art numerical models at the scale of the whole salt pillow or salt dome to define the "ist-Zustand". All these contributions are closely integrated and will lead to much improved prediction of the evolution of the caverns after closure and abandonment.

Burning of clinker is the most influencing step of cement quality during the production process. Appropriate characterisation for quality control and decision-making is therefore the critical point to maintain a stable production but also for the development of alternative cements. Scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDX) delivers spatially resolved phase and chemical information for cement clinker. This data can be used to quantify phase fractions and chemical composition of identified phases. The contribution aims to provide an overview of phase fraction quantification by semi-automatic phase segmentation using high-resolution backscattered electron (BSE) images and lower-resolved EDX element maps. Therefore, a tool for image analysis was developed that uses state-of-the-art algorithms for pixel-wise image segmentation and labelling in combination with a decision tree that allows searching for specific clinker phases. Results show that this tool can be applied to segment sub-micron scale clinker phases and to get a quantification of all phase fractions. In addition, statistical evaluation of the data is implemented within the tool to reveal whether the imaged area is representative for all clinker phases.

Summary While the influence of clay smear on the sealing properties of fault zones in siliciclastic rocks can be predicted by validated concepts such as the SGR or CSP reliable models for predicting the structural and hydraulic properties of faults in layered limestone-marl sequences do not yet exist. The main goal of our study is to analyse the development of fault sealing as a result of marl smearing in interaction with mechanical mixing as well as fracturing and cementation processes in dependence of mechanically alternating bedding and fault geometry. Oriented transfer samples of fault cores from different normal fault systems destabilised by the fault process with adjacent damage zone were successfully extracted from outcrops with Jurassic limestone in a quarry Northern Bavaria, Germany. Microanalytical tools and multiscale (m-nm) analyses workflows were developed to provide ground truth for the training of machine learning algorithms for the efficient interpretation of 2D microstructural image data. The systematic macroscopic and microstructural examination of the transfer specimens has shown that the fault zones are built up by recurrent building blocks, whose variation and expression are strongly influenced by the presence and nature of interbedded marly layers.

Abstract Tight carbonate rocks are important potential although unconventional geothermal and hydrocarbon underground storage reservoirs and prospective CO 2 -EGS sites. We study these rocks by using the Upper Jurassic “Malm ß” in Southern Germany as an outcrop analog example to understand bulk properties in relation to microstructure and to test a variety of models for permeability prediction. Bulk petrophysical methods (Archimedes isopropanol immersion method, Helium pycnometry, mercury injection capillary pressure, gamma density core logging, gas permeability measurements) combined with microstructural investigations (BIB-SEM) are applied. Samples are macroscopically undeformed limestones collected from a tectonically overprinted quarry wall near the town of Simmelsdorf (38 km NE of Nürnberg city). Bulk porosities are below 5% and argon permeabilities are on average 1.4E-17m 2 . The presence of stylolites in some of the samples has neither a significant effect on porosity nor permeability. Pore sizes are in the submicron range and the diagenetically lithified stiff limestones are characterized by a relatively high Young’s Modulus averaging 73±5 MPa. Moreover, no trends in properties were observable towards the faults, indicating that faulting was post-diagenetic and that the matrix permeabilities were too low for intensive post-diagenetic fluid-rock interaction. Petrophysical properties are very close to those measured in stratigraphic equivalent rocks of the South German Molasse Basin, illustrating the widespread homogeneity of these rocks and justifying the quarry scale (500 x 580 m) as a reasonable reservoir analog for these rocks in the subsurface. The application of various permeability prediction models showed that the Capillary Tube model and the Saki Model are very well suited for predicting permeabilities from BIB-SEM and mercury injection capillary pressure results, respectively. We thereby found that the matrix permeability is primarily controlled by the pore throat diameters rather than the effective porosity.

Commercial carbon fiber (CF) fabrics are popular electrode materials for bioelectrochemical systems (BES), but are usually not optimized for the specific application. This study investigates BES-relevant material characteristics on fabric level, such as weave types and weave parameters. The two contrasting weave types plain and leno weave were characterized with respect to their envisaged application types: 1) BES with mainly advective flow regimes and 2) stirred systems, which could benefit from fluid flow through a fabric electrode. Experiments with batch and continuously fed pure cultures of Geobacter sulfurreducens PCA and Shewanella oneidensis MR-1 reveal that µm-scale electrode topologies are of limited use for the thick biofilms of G. sulfurreducens, but can boost S. oneidensis’ current generation especially in batch and fed-batch reactors. For advective flow regimes, deeper layers of biofilm inside microporous electrodes are often mass transport limited, even with thin biofilms of S. oneidensis. Therefore, low porosity plain weave electrodes for advective flow operation as in wastewater treating BES should be thin and flat. A trade-off between maximized current density and electrode material utilization exists, which is optimized exemplarily for an advective flow operation. For stirred BES of biotechnological applications, a flow-through of electrolyte is desired. For this, leno weave fabrics with pores at cm-scale are produced from 100% CF for the first time. In a preliminary evaluation, they outperform plain weave fabrics. Mass transfer investigations in stirred BES demonstrate that the large pores enable efficient electrode utilization at lower power input in terms of stirring speed.

A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical tests have been performed to characterise the bulk mechanical, hydro-mechanical, and failure behaviour of Opalinus Clay, important questions remain about micromechanisms: how do microstructural evolution and deformation mechanisms control the complex rheology? What is the in situ microstructural shear evolution, and can it be mimicked in the laboratory? In this contribution, scanning electron microscopy (SEM) was used to image microstructures in an Opalinus Clay sample deformed in an unconsolidated–undrained triaxial compression test at 4 MPa confining stress followed by argon broad ion beam (BIB) polishing. Axial load was applied (sub-)perpendicular to bedding until the sample failed. The test was terminated at an axial strain of 1.35 %. Volumetric strain measurements showed bulk compaction throughout the compression test. Observations on the centimetre to micrometre scale showed that the samples exhibited shear failure and that deformation localised by forming a network of micrometre-wide fractures, which are oriented with angles of 50∘ with respect to horizontal. In BIB–SEM at the grain scale, macroscale fractures are shown to be incipient shear bands, which show dilatant intergranular and intragranular microfracturing, granular flow, bending of phyllosilicate grains, and pore collapse in fossils. Outside these zones, no deformation microstructures were observed, indicating only localised permanent deformation. Thus, micromechanisms of deformation appear to be controlled by both brittle and ductile processes along preferred deformation bands. Anastomosing networks of fractures develop into the main deformation bands with widths up to tens of micrometres along which the sample fails. Microstructural observations and the stress–strain behaviour were integrated into a deformation model with three different stages of damage accumulation representative for the deformation of the compressed Opalinus Clay sample. Results on the microscale explain how the sample locally dilates, while bulk measurement shows compaction, with an inferred major effect on permeability by an increase in hydraulic conductivity within the deformation band. Comparison with the microstructure of highly strained Opalinus Clay in fault zones shows partial similarity and suggests that during long-term deformation additional solution–precipitation processes operate.

To improve the understanding of gas transport processes in tight rocks (e.g., shales), systematic flow tests with different gases were conducted on artificial micro- to nanoporous analogue materials. Due to the rigidity of these systems, fluid-dynamic effects could be studied at elevated pressures without interference of poro-elastic effects. Flow tests with narrow capillaries did not reveal any viscosity anomaly in a confined space down to capillary diameters of 2 µm. Experiments with nanoporous ceramic disks (> 99% Al 2 O 3 ) conducted at confining pressures from 10 to 50 MPa did not indicate any stress dependence of permeability coefficients. Analysis of the apparent permeability coefficients over a mean gas pressure range from 0.2 to 30.5 MPa showed essentially linear Klinkenberg trends with no indication of second-order slip flow. The Klinkenberg-corrected permeability coefficients measured with helium were consistently higher than those measured with all other gases under the same conditions. This “helium anomaly” was, however, less pronounced than the same effect observed in natural rocks, indicating that it is probably not related to fluid-dynamic effects but rather to gas–solid interactions (e.g., sorption). Permeability tests with CO 2 on the nanoporous membrane show significant deviations from the linear Klinkenberg trend around the critical point. This is due to the drastic changes of the thermodynamic properties, in particular the isothermal compressibility, in this pressure and temperature range. Helium pycnometry, mercury intrusion porosimetry and low-pressure nitrogen sorption showed good agreement in terms of porosity (~ 28%) and the most prominent pore diameter (~ 68.5 nm).

Summary Carbonate rocks are heterogeneous at microscopic and macroscopic scales, hence, their characterization is challenging, expensive and time-consuming. Petrophysical analyses cannot provide information on the full geometry and pore space connectivity. Moreover, these analyses are time consuming and require evaluation by experts. Current imaging techniques do not cover a representative range of scales, have difficulty to image microporosity, and are not well integrated with the expert knowledge available. An automated tool for identifying and classifying pores and fractures does not yet exist. This contribution presents a novel multi-scale workflow dedicated to carbonate rocks that integrates innovative methods with state-of-the-art imaging technologies for automated classification of connected pores from nano- to centimeter scale: 1) Virtual Petrograph (ViP), an automated high resolution petrographic microscope to acquire and visualize high-resolution cross-polarized image-maps of ultra-thin sections; 2) Broad Ion Beam – Scanning Electron Microscopy (BIB-SEM), a 2D preparation and imaging technique that preserves the most delicate microstructures and images microporosity in detail over representative areas; 3) Liquid Metal Injection (LMI) followed by BIB-SEM, a porosimetry technique to distinguish connected and unconnected pore space. Validated pore maps will be the input for statistical analysis and used to train deep learning algorithms for pore segmentation and classification.

Abstract. A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical laboratory tests have been performed to characterize the bulk mechanical, hydro-mechanical and failure behaviour of Opalinus Clay, important questions remain about microphysics: How do microstructural evolution and deformation mechanisms control the 15 complex rheology over time scales not accessible in the laboratory. In this contribution, Scanning Electron Microscopy (SEM) was used to image microstructures in an Opalinus Clay sample deformed in an unconsolidated-undrained triaxial compression test at 4 MPa confining stress followed by Argon Broad Ion Beam (BIB) polishing. Axial load was applied (sub-) perpendicular to bedding until the specimen failed. The test was terminated at an axial strain of 1.35 %. Volumetric strain measurements showed bulk compaction throughout the compression test. Observations on the cm- to μm-scale showed that deformation 20 localized by forming a network of μm-thick fractures. In BIB-SEM at the grain scale, incipient deformation zones show dilatant inter- and intragranular micro-cracking, granular flow, plastic deformation and bending of phyllosilicate grains, and pore collapse in fossils. Outside these zones, no deformation microstructures were observed indicating localized damage. Thus, microphysics of deformation appear to be controlled by both brittle and ductile processes along preferred orientations. Anastomosing networks of deformation bands develop into the main deformation bands along which the sample fails. 25 Microstructural observations and the stress-strain behaviour were integrated into a deformation model with three different stages of damage accumulation representative for the deformation of the compressed Opalinus Clay sample. Results on the microscale explain how the sample locally dilates while bulk measurement shows compaction, with an inferred major effect on permeability evolution. Comparison with the microstructure of highly strained Opalinus Clay in fault zones shows minor similarity and suggest that during long-term deformation additional solution-precipitation processes operate.