Effect of Water on Effective Pore Structures for Medium-Rank Coal: Based on the Prefreezing Nitrogen Adsorption-Desorption Experiment

Water is ubiquitous in coal reservoirs, and its distribution can have a remarkable influence on the effective pore space of methane. This study conducted the combination experiments of moisture equilibrium and prefreezing nitrogen adsorption-desorption to explore the adsorption behavior of water in coal pores and thus to reveal the distribution characteristics of water in pores with different scales as well as the influence of water on pore structures. The results showed that the adsorption mechanism of water vapor undergoes a transition from monolayer to multilayer to condensation with the increase in relative humidity (RH). The occurrence characteristics of adsorbed water in coal pores are controlled by the RH and pore size. When the RH is increased from 0 to 98%, the nitrogen adsorption capacity, specific surface area, and effective pore volume of the samples were all decreased significantly due to the different adsorption modes of water, which is more significant in pores with d < 10 nm. Additionally, the relative pressure corresponding to the branching position of the nitrogen adsorption-desorption curve will be changed with the increase in moisture content. Based on this, it is calculated that the adsorbed water will change the smoothness of the pore wall and the complexity of the pore structure.

Physicochemical characterization of dapagliflozin and its solid-state behavior in stress stability test

As an active pharmaceutical ingredient, dapagliflozin propanediol monohydrate (D-PD) has been used in the solvated form consisting of dapagliflozin compounded with (S)-propylene glycol and monohydrate at a 1:1:1 ratio. However, dapagliflozin propanediol loses the solvent's reduced lattice structure at slightly higher temperatures. Due to its sensitive solid-state stability, the temperature and humidity are strictly controlled during the production and storage of dapagliflozin. Thus, crystalline molecular complexes containing pharmaceutical salts, solvates, monohydrates, and cocrystals have recently been developed as alternative strategies. This study investigated the dapagliflozin free base (D-FB), D-PD, and dapagliflozin l-proline cocrystals (D-LP). Their solid-state behavior was also evaluated in stress stability studies. The compounds were analyzed using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier-transform infrared (FT-IR) spectroscopy, dynamic vapor sorption (DVS), and powder rheology testing. In addition, Carr's index, the Hausner ratio, contact angle, and intrinsic dissolution rate were calculated. Dapagliflozin exhibited distinct physical properties depending upon the differences in solid form and also showed significant differences in solid-state behavior in the stress stability test. In conclusion, D-LP was superior to D-FB or D-PD in physicochemical and mechanical properties.

Experimental Investigation of Gas Dynamic Effects Using Nanoporous Synthetic Materials as Tight Rock Analogues

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% Al2O3) 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 CO2 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).

Model-free classification of X-ray scattering signals applied to image segmentation

This article describes a modeling framework to relate the molecular orientation of nanostructures to polarized resonant soft X-ray scattering measurements using the Born approximation and a full tensor treatment.

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.

Geomechanical and petrophysical properties of mudrocks: introduction

Mudstones (shales) are of particular importance as the source rocks for oil and gas, and increasingly so as the reservoirs for unconventional hydrocarbons. They are also the most common sedimentary rocks on Earth, and, hence, are frequently encountered in excavations and foundations for buildings. These factors point to a pressing need to develop an increased fundamental understanding of their geomechanical and petrophysical properties. The mineral content of mudstones has a dominant effect on their mechanical properties. Presence of clay minerals within them results in plasticity and ductility that can pose particular engineering challenges, but swelling clays in particular can lead to serious problems of mechanical stability of boreholes and in construction. Good hydraulic fracture performance is linked to brittleness and high elastic moduli. This in turn is favoured by high silica or carbonate content and diagenetic cementation. Permeability to fluids depends on the interconnectivity of storage pores through orientated crack networks. New advances in imaging technologies are permitting very-high-resolution three-dimensional imaging down to the nanometre scale. Such studies will eventually lead to technological advances that exploit more effectively these enigmatic rocks.