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 N 2 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.

Abstract Low-permeability (unconventional) reservoirs exhibit heterogeneities at multiple scales that affect flow. While macro-scale heterogeneities are typically evaluated using well-test or production-analysis techniques, core-scale (and finer) analyses are relied upon to evaluate micro-and nano-scale heterogeneities. Pore structure is a known control on flow at the core scale; for unconventional reservoirs, however, pore-size distributions, pore accessibility, and connectivity are challenging to evaluate. In the present study, a combination of neutron-scattering methods, fluid invasion, and imaging techniques were used to evaluate the degree of pore accessibility and connectivity in a tight oil reservoir within the Cardium Fm. of western Canada. In previous work, cm- to sub-cm scale variations in lithology (elementary lithological components, or ELCs) have been shown to affect flow at the core scale significantly and that reservoir quality varies with the ELCs. The fundamental controls on flow within these ELCs ( i.e. at the pore scale), however, are poorly understood. The aim of the present study was to gain insight into these controls. Small-angle and ultra-small angle neutron scattering (SANS/USANS) has revealed that while the Cardium samples exhibit a wide range in pore-size distribution, the accessibility of pores varies significantly with pore size. In particular, the large pore fraction seems to be less accessible than the small pore fraction, which is counter-intuitive. Mercury intrusion data partially support this finding. High-resolution scanning electron microscopy (SEM) imaging suggests that pores within mineral grains may indeed be disconnected/isolated. The SANS/USANS interpretations are based on a simple 2-component (pores + average mineral phase) model, however; detailed mineral mapping reveals that several components may affect significantly the scattering behavior which leads to the conclusion that a multi-phase model may be more appropriate, and that use of the conventional 2-phase model could lead to errors in calculated pore-size distributions and the percentage of disconnected porosity.

Abstract Total scattering experiments using synchrotron X-rays and spallation neutrons are providing new insights into the structural characteristics of synthetic and natural ferrihydrite, a poorly crystalline nanomineral that has industrial applications and is pervasive in the environment. Modern synchrotron and neutron facilities with dedicated total scattering beamlines now enable the collection of scattering data for ferrihydrite to large scattering angles and with superior signal/noise ratio. The pair distribution function, or PDF, derived from these scattering data is a real-space depiction of atomic structure with exceptional resolution. A number of recent high-energy X-ray total scattering studies have focused on as-precipitated, pure synthetic ferrihydrite of different particle sizes, as well as ferrihydrite co-precipitated with environmentally relevant impurities, such as aluminum, arsenic, chromium, and silicon. The findings from these investigations have contributed to our understanding of the extended framework of iron and oxygen in ferrihydrite, and the specific associations of these various impurities over a range of impurity content. In situ and ex situ synchrotron total scattering methods are being applied in studies of the structural, physical, chemical, and magnetic changes taking place during ferrihydrite transformations. Neutron total scattering is shedding new light on the association of water with the surfaces and in the bulk structure of ferrihydrite. In several of these studies, real-space fitting of PDFs derived from both neutrons and X-rays are being used to test both new and previously proposed structural models for synthetic ferrihydrite. Total scattering and PDF analysis is also revealing new insights into the structural characteristics of different samples of natural ferrihydrite that were formed in a diverse range of geochemical settings. The results of these studies, combined with new PDF data for a suite of natural samples presented in this review, show that the structure of natural ferrihydrite can vary almost continuously between high- and low-crystallinity end members. The natural samples with the greatest degree of structural order are virtually identical to pure laboratory ‘six-line’ ferrihydrite. Interestingly, total scattering shows that the majority of the natural ferrihydrite samples in the suite presented here are less crystalline than ‘two-line’ ferrihydrite, the variety of synthetic ferrihydrite that is often assumed in laboratory studies to be equivalent to natural ferrihydrite. The implications of this decreased crystallinity are not yet fully understood in terms of evaluating and predicting the chemical behavior of natural ferrihydrite in the environment.

Abstract Following the discovery of X-ray scattering on crystalline materials, crystallography and the experimental application of diffraction techniques have resulted in our current understanding of the atomic arrangements and bonding in condensed phases. Soon after Max von Laue’s famous experiments in 1912 (Fig. 1 ), for which he received the Nobel Prize in Physics in 1914, a period of pioneering work began. Starting with father and son Bragg in the early twenties, the “century of crystal-structure determination” brought insight to the atomic view of solid matter, which only had been a matter of speculation before the discovery of scattering by crystals. Scattering techniques were de-veloped over the subsequent years, not only using X-ray radiation, but also involving electron and neutron scattering phenomena. Nowadays, with the evolution of powerful radiation sources, such as neutron spallation sources or synchrotron radiation facilities, the nature of atomic structure can be visualised even for the most complex macromolec-ular systems which include thousands of atoms. The pioneering work of structure solution was carried out at ambient conditions, starting with basic structures such as of sodium chloride, zincblende or diamond. Structure solution was not straightforward from the beginning. The so-called “phase problem”, i.e. the fact that the amount of phase shift on wave interference could not be determined experimentally from diffraction data, kept crystallographers busy for decades. It resulted in fundamental approaches, such as the Fourier summation of a set of squared (but not phased) amplitudes as introduced by A.L. Patterson (1934) . H. Hauptman and J. Karle (1950) employed statistics and probability distributions as applied in the “direct methods” to overcome the phase problem.

Abstract Understanding the structure of the Earth's interior, only indirectly inferred from seismic observations, requires modelling based on structural data, and the thermodynamic properties and phase relations of minerals at high pressures and temperatures. Since experimental studies under these conditions are often limited, particularly on high pressure phases that can be synthesised in only very small amounts, an important objective of earth sciences is to develop the capability of predicting these properties under various pressure and temperature conditions prevalent in the Earth. It is now possible to theoretically explore the entire spectrum of thermal vibrations of crystals using lattice dynamical methods. The vibrational average, known as the phonon density of states, is the basis for the calculation of the various thermodynamic properties. The accuracy of the theoretical calculations of the phonon density of states and the phonon dispersion relations can be evaluated by comparison with their experimental measurements by inelastic neutron scattering on large powder and single crystal samples, respectively. In this paper, the theory of lattice dynamics and inelastic neutron scattering and the experimental measurements using neutrons from reactor and spallation sources are reviewed, along with the derivation of thermodynamic properties from the calculated phonon density of states. Work accomplished in this area, both theoretical and experimental, on a number of major rock forming silicate minerals, including olivine (forsterite and fayalite), enstatite, various garnets and the aluminium silicate polymorphs (andalusite, sillimanite and kyanite) are discussed. We start with a discussion of lattice dynamics in a single crystal. A crystal is often

Abstract X-ray and neutron single crystal diffraction, now paralleled by powder diffraction techniques, is the principal tool for the experimental investigation of crystal structures. For the most part the information obtained is the volume averaged model of the atom arrangement in the crystal, so that only a small subset of the published structural studies advance beyond the determination of atomic positions and site occupancies in the crystallographic cell. However, it is well proven that the analysis of accurately measured diffraction intensities may yield important physico-chemical information, such as the electron density distribution, the vibrational behaviour of the atoms about their average positions, or the potential energy of the molecular conformation in the crystal. The main scope of this contribution is to emphasise the importance of the experimentally derived atomic displacement parameters obtained by diffraction methods from ordered crystal structures. A few concepts will be illustrated using cuprite-type structures as case studies: (1) the advantage of neutron nuclear scattering over X-ray scattering by electrons in discriminating the vibrational contribution from the charge density contribution to the apparent atomic displacement behaviour; (2) the use of the temperature dependence of the atomic displacement parameters in the detection of site disorder effects; (3) the comparison of atomic displacement parameters as extracted from diffraction and spectroscopic data; (4) the use of neutron single crystal diffraction in detecting the anharmonic contribution to the overall harmonic atomic vibrational behaviour. It is argued that the accurate measurement