In geoenergy applications, mudrocks prevent fluids to leak from temporary (H 2 , CH 4 ) or permanent (CO 2 , radioactive waste) storage/disposal sites and serve as a source and reservoir for unconventional oil and gas. Understanding transport properties integrated with dominant fluid flow mechanisms in mudrocks is essential to better predict the performance of mudrocks within these applications. In this study, small-angle neutron scattering (SANS) experiments were conducted on 71 samples from 13 different sets of mudrocks across the globe to capture the pore structure of nearly the full pore size spectrum (2 nm–5 μm). We develop fractal models to predict transport properties (permeability and diffusivity) based on the SANS-derived pore size distributions. The results indicate that transport phenomena in mudrocks are intrinsically pore size-dependent. Depending on hydrostatic pore pressures, transition flow develops in micropores, slip flow in meso- and macropores, and continuum flow in larger macropores. Fluid flow regimes progress towards larger pore sizes during reservoir depletion or smaller pore sizes during fluid storage, so when pressure is decreased or increased, respectively. Capturing the heterogeneity of mudrocks by considering fractal dimension and tortuosity fractal dimension for defined pore size ranges, fractal models integrate apparent permeability with slip flow, Darcy permeability with continuum flow, and gas diffusivity with diffusion flow in the matrix. This new model of pore size-dependent transport and integrated transport properties using fractal models yields a systematic approach that can also inform multiscale multi-physics models to better understand fluid flow and transport phenomena in mudrocks on the reservoir and basin scale.

Summary We apply scanning SAXS and WAXS microscopy to different mudrock samples. The method characterizes the microstructure in terms of porosity and preferential pore alignment of small pores 6 −202 nm size. These small features are experimentally challenging to resolve for statistically relevant sample volumes with state of the art characterization techniques, such as imaging methods. A key novelty in this study is the quantification of the mineralogy and mineral phase content from the WAXS measurements. Thus, a detailed quantification and comparison of important microstructural parameters is achieved. The method is used in a raster scanning mode, where thousands of consecutive measurements are performed, with a high micrometric spatial resolution, over mm sized sample areas. Therefore, simultaneously the variation of the microstructure is resolved on the pore and lamina scale. We propose to use scanning SAXS-WAXS microcopy in future studies for investigations of the systematic relationships between mineralogy and the pore network.

Summary The pore structure of organic rich mudrocks is associated with both inorganic and organic constituents. The contribution of organic matter to the pore structure has been investigated on Posidonia and Bossier Shale samples having different organic carbon content and thermal maturity. Development and distribution of organic matter pores were studied by using small angle neutron scattering technique at a broad pore scale size investigation, from 2 nm to 2 µm. The pore structure of the mudrocks studied is highly complicated at which total pore volume and specific surface area are not significantly affected by thermal maturation, however, the maturity attribute contributes to different pore size distribution on meso- and macro-pores. Thermal maturation is likely to be the factor of amalgamating small organic matter pores into larger pores in overmature organic rich mudrocks, potentially causing an increase in pore volume at macroscale pores. Although not considerably, the increased macroporosity can enhance the permeability of pore network for viscous gas flow in organic rich mudrocks.

When dust and other particulates accumulate on the surface of solar modules, the power output of these soiled modules is significantly reduced. To combat this issue, antisoiling coatings can be placed on the top glass surface of solar modules. While there exists some understanding of how antisoiling coatings reduce soiling and reflection losses, approaches to characterize the durability and stability of the chemistry and morphology of antisoiling PV glass module coatings and how they evolve in response to soiling interactions are currently underdeveloped. Here we present the use of small-angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) as a methodology for studying the morphology and chemistry of pristine and soiled antisoiling coatings. This work demonstrates the effectiveness of SAXS in observing coating morphology despite the presence of soil surface layers-a capability which sets it apart as a strong characterization tool for antisoiling coatings on PV glass. XPS and XAS are used as complementary techniques to characterize the evolution of coating surface chemistry before and after soiling. XAS is shown to detect subtle chemical changes in the coating surface that cannot be detected by XPS.

Summary Small angle neutron scattering (SANS) and nitrogen low-pressure adsorption (LPS) have been used to characterise the pore structure of two organic lean mudrocks, Opalinus Clay, Mont Terri, Switzerland and Carmel Claystone, Utah. This was done in order to obtain a better understanding of H2 and CO2 transport, reaction and sorption related to radioactive waste disposal and carbon storage, respectively. The pore structure information derived by SANS and LPS are comparable and the results have revealed a vast heterogeneity from 2 nm to 2 µm, which can be related to the high clay contents. Due to the high clay contents, pores smaller than 10 nm constitute a large fraction of total porosity (25–30 %) and most of specific surface area (up to 80 %) in the sample mudrocks. Accordingly, these interplays contribute to a pore network of few-to-several nano-Darcy permeability in which pore size dependent transport mechanisms can vary from high sorptive diffusional fluid flow in small pores to low sorptive slip flow regime at progressively larger pores.

In most cases, the analysis of small-angle and wide-angle X-ray scattering (SAXS and WAXS, respectively) requires a theoretical model to describe the sample's scattering, complicating the interpretation of the scattering resulting from complex heterogeneous samples. This is the reason why, in general, the analysis of a large number of scattering patterns, such as are generated by time-resolved and scanning methods, remains challenging. Here, a model-free classification method to separate SAXS/WAXS signals on the basis of their inflection points is introduced and demonstrated. This article focuses on the segmentation of scanning SAXS/WAXS maps for which each pixel corresponds to an azimuthally integrated scattering curve. In such a way, the sample composition distribution can be segmented through signal classification without applying a model or previous sample knowledge. Dimensionality reduction and clustering algorithms are employed to classify SAXS/WAXS signals according to their similarity. The number of clusters, i.e. the main sample regions detected by SAXS/WAXS signal similarity, is automatically estimated. From each cluster, a main representative SAXS/WAXS signal is extracted to uncover the spatial distribution of the mixtures of phases that form the sample. As examples of applications, a mudrock sample and two breast tissue lesions are segmented.

The determination of effective diffusion coefficients of gases or solutes in the water‐saturated pore space of mudrocks is time consuming and technically challenging. Yet reliable values of effective diffusion coefficients are important to predict migration of hydrocarbon gases in unconventional reservoirs, dissipation of (explosive) gases through clay barriers in radioactive waste repositories, mineral alteration of seals to geological CO 2 storage reservoirs, and contaminant migration through aquitards. In this study, small‐angle and very small angle neutron scattering techniques have been utilized to determine a range of transport properties in mudrocks, including porosity, pore size distributions, and surface and volume fractal dimensions of pores and grains, from which diffusive transport parameters can be estimated. Using a fractal model derived from Archie's law, we calculate effective diffusion coefficients from these parameters and compare them to laboratory‐derived effective diffusion coefficients for CO 2 , H 2 , CH 4 , and HTO on either the same or related mudrock samples. The samples include Opalinus Shale from the underground laboratory in Mont Terri, Switzerland, Boom Clay from a core drilled in Mol, Belgium, and a marine claystone cored in Utah, USA. The predicted values were compared to laboratory diffusion measurements. The measured and modeled diffusion coefficients show good agreement, differing generally by less than factor 5. Neutron or X‐ray scattering analysis is therefore proposed as a novel method for fast, accurate estimation of effective diffusion coefficients in mudrocks, together with simultaneous measurement of multiple transport parameters including porosity, pore size distributions, and surface areas, important for (reactive) transport modeling.

Abstract Porosity of shales is an important parameter that impacts rock strength for seal or wellbore integrity, gas-in-place calculations for unconventional resources or the diffusional solute and gas transport in these microporous materials. From a well section obtained from the Mont Terri Underground Rock Laboratory in St Ursanne, Switzerland, we determined porosity, pore size distribution and specific surface areas on a set of 13 Opalinus Clay samples. The porosity methods employed are helium-pycnometry, water and mercury injection porosimetry, liquid saturation and immersion, and low pressure N2 sorption, as well as small-angle to ultra-small-angle neutron scattering (SANS–USANS). These were used in addition to mineralogical and geochemical methods for sample analysis that comprise X-ray diffraction, X-ray fluorescence, total organic carbon content and cation exchange capacity. We find large variations in total porosity, ranging from approximately 23% for the neutron-scattering method to approximately 10% for mercury injection porosimetry. These differences can partly be related to differences in pore accessibility, while no or negligible inaccessible porosity was found. Pore volume distributions between neutron scattering and low-pressure sorption compare very well but differ significantly from those obtained from mercury porosimetry: this is realistic since the latter provides information on pore throats only, and the two former methods on pore throats and pore bodies. Finally, we find that specific surface areas determined using low-pressure sorption and neutron scattering match well.

Summary The determination of fabric and pore structure of shales remains a challenging task which is mainly due to the wide range of pore sizes (and shapes) ranging from molecular dimensions to microns. High resolution imaging techniques fail to provide information over representative regions of interest, while more conventional characterization techniques may only assess volume averaged properties of the pore systems. Thus, open questions remain regarding the effects of the multi-scale pore network of shales in the retention and transport of hydrocarbons during unconventional production processes. We apply scanning small- and wide-angle X-ray scattering (SAXS and WAXS) microscopy to obtain averaged but detailed information from the micro- and meso-pore structures of shales. By combining SAXS/WAXS with raster-scanning microscopy, we obtain local scattering information from 1–100 nm-size pores in micrometer-size volumes over a large (2 × 2) mm2 scanning area. We derive porosity, pore size distribution and orientation, as well as mineralogy of specially prepared thin section samples, covering length scale ranges of nm to sub-microns and from microns to millimeters, with a gap that can potentially be closed The method further enables the linking of porosity to shale matrix components, which is integrated in a multi-scale imaging workflow involving μCT, and SEM/EDX analysis, aimed at allowing for the full pore network characterization of shales.

The pore space of shales and mudrocks ranges from molecular dimensions to micrometers in length scale. This leads to great variation in spatial characteristics across many orders of magnitude, which poses a challenge for the determination of a representative microscopic pore network for such systems. Standard characterization techniques generally provide volume averaged properties while high-resolution imaging techniques do not assess a representative range of pore sizes because of limitations in the spatial resolution over the field of view. Due to this complexity, open questions remain regarding the role of the pore network in retention and transport processes, which in turn control oil and gas production. Volume-averaged but spatially resolved information is obtained for pores of size from 2 to 150 nm by applying scanning small- and wide-angle X-ray scattering (SAXS and WAXS) microscopy. Scattering patterns are collected in a scanning microscopy mode, such that microvoxels are sampled sequentially, over a total of 2 x 2 mm(2) raster area on specifically prepared thin sections with a thickness of 10-30 /Am. Spatially resolved variations of porosity, pore-size distribution, orientation, as well as mineralogy are derived simultaneously. Aiming at a full characterization of the shale pore network, the measurements and subsequent matrix porosity analysis are integrated in a multiscale imaging workflow involving FIB-SEM, SEM, and mu-CT analysis.

Summary While the determination of porosity on sandstones is well established, porosities determined on shales are much less straightforward due to limited coring or inadequate pore preservation. Porosity in shale has an important control on many petrophysical, geomechanical and geochemical parameters of shales. Most of the porosity in shales is associated with small pore throat sizes, ranging in diameter from few up to about 100 nm. Pore throat sizes in carbonate or sandstone reservoir rocks are typically determined using mercury injection porosimetry (MIP). It is however well understood that MIP on shales underestimates porosity due to its limited accessibility. It is well known that using different methods for determining shale porosity results in different porosity values which is due to the different accessibility. Nonetheless, porosity is generally used as an absolute, intrinsic parameter without considering the method for determination. To address this issue we compare porosity, specific surface areas and pore volume distributions from fluid invasion and radiation methods on a total of 14 different Opalinus Clay samples recovered from the shaly facies at the Mont Terri underground laboratory in St. Ursanne, Switzerland.

During imbibition, initially connected oil is displaced until it is trapped as immobile clusters. While initial and final states have been well described before, here we image the dynamic transient process in a sandstone rock using fast synchrotron‐based X‐ray computed microtomography. Wetting film swelling and subsequent snap off, at unusually high saturation, decreases nonwetting phase connectivity, which leads to nonwetting phase fragmentation into mobile ganglia, i.e., ganglion dynamics regime. We find that in addition to pressure‐driven connected pathway flow, mass transfer in the oil phase also occurs by a sequence of correlated breakup and coalescence processes. For example, meniscus oscillations caused by snap‐off events trigger coalescence of adjacent clusters. The ganglion dynamics occurs at the length scale of oil clusters and thus represents an intermediate flow regime between pore and Darcy scale that is so far dismissed in most upscaling attempts.

The onset of oil mobilization during imbibition has been imaged with pore-scale resolution under dynamic flow conditions viscocapillary balance, by using fast synchrotron-based X-ray computed microtomography. Oil mobilization under unsteady-state displacement has been studied for sintered glass, sandstone and carbonate rock, which demonstrate distinctly different behavior with respect to the cluster-size distributions and respective time evolution.For the sandstone sample, which showed the largest saturation change between the three samples, over 50% of the oil was mobilized during imbibition. The cluster-size distribution computed from the tomography images, but also detailed visualization at the pore scale revealed that during imbibition the largest (initially connected) cluster breaks off into smaller segments. Over time, successively larger segments break off, which increases the frequency of intermediate-size clusters. In most cases, each segment breaks off into even smaller segments, but also in fewer cases clusters merge and increase in size.These findings support the view that at the onset of oil-mobilization clusters prefer to break off instead of moving as a large cluster, which gives further insight into the ganglion dynamics flow regime. It is also shown that imbibition dynamics is more complex than assumed under common percolation models, where, for instance, disconnected nonwetting-phase clusters become immobile and remain static. The experimental data instead clearly show time evolution for disconnected clusters that can lead to reconnection or further break off.

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 m. 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 -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.

Pore-scale events in multiphase flow in porous rock have been directly imaged in real time by using fast (15 to 60 seconds) synchrotron-based X-ray computed microtomography. In the past, pore-scale fluid displacements in porous media could only be imaged under quasistatic conditions where at scanning times of several minutes to hours, fluid distributions were subject to capillary redistribution. Here, pore-scale displacement events in porous rock were imaged in situ in real time in natural rock under dynamic flow conditions, where the pressure gradient and the viscocapillary balance were maintained during scanning. Two elementary processes, Haines jumps in drainage and snap-off in imbibition, were studied in detail for sintered glass, sandstone, and carbonate rock. We found that most Haines jump events do not displace the wetting phase pore-by-pore, but typically involve 10 to 20 individual pores and that filling events are cooperative. We also found that in sandstone rock 64% of the externally applied work is actually dissipated during these jumps and approximately 36% is converted into interfacial energy.

Newly developed high-speed, synchrotron-based X-ray computed microtomography enabled us to directly image pore-scale displacement events in porous rock in real time. Common approaches to modeling macroscopic fluid behavior are phenomenological, have many shortcomings, and lack consistent links to elementary pore-scale displacement processes, such as Haines jumps and snap-off. Unlike the common singular pore jump paradigm based on observations of restricted artificial capillaries, we found that Haines jumps typically cascade through 10-20 geometrically defined pores per event, accounting for 64% of the energy dissipation. Real-time imaging provided a more detailed fundamental understanding of the elementary processes in porous media, such as hysteresis, snap-off, and nonwetting phase entrapment, and it opens the way for a rigorous process for upscaling based on thermodynamic models.

X-ray computed microtomography reveals the internal features of pearls with great detail. This method is useful for identifying some of the natural or cultured pearls that are difficult to separate using traditional X-radiography The long measurement time, the cost of the instrumentation, and the fact only one pearl at a time can be imaged are some of this method's disadvantages.