In-situ synchrotron characterization of fracture initiation and propagation in shales during indentation

The feasibility and advantages of synchrotron imaging have been demonstrated to effectively characterise fracture initiation and propagation in shales during indentation tests. These include 1) fast (minute-scale) and high-resolution (μm-scale) imaging of fracture initiation, 2) concurrent spatial and temporal information (4D) about fracture development, 3) quantification and modelling of shale deformation prior to fracture. Imaging experiments were performed on four shale samples with different laminations and compositions in different orientations, representative of three key variables in shale microstructure. Fracture initiation and propagation were successfully captured in 3D over time, and strain maps were generated using digital volume correlation (DVC). Subsequently, post-experimental fracture geometries were characterized at nano-scale using complementary SEM imaging. Characterisation results highlight the influence of microstructural and anisotropy variations on the mechanical properties of shales. The fractures tend to kink at the interface of two different textures at both macroscale and microscale due to deformation incompatibility. The average composition appears to provide the major control on hardness and fracture initiation load; while the material texture and the orientation of the indentation to bedding combine to control the fracture propagation direction and geometry. This improved understanding of fracture development in shales is potentially significant in the clean energy applications

Linking multi-scale 3D microstructure to potential enhanced natural gas recovery and subsurface CO2 storage for Bowland shale, UK

Injection of CO2 into shale reservoirs to enhance gas recovery and simultaneously sequester greenhouse gases is a potential contributor towards the carbon-neutral target. It offers a low-carbon, low-cost, low-waste and large-scale solution during the energy transition period. A precondition to efficient gas storage and flow is a sound understanding of how the shale’s micro-scale impacts on these phenomena. However, the heterogeneous and complex nature of shales limits the understanding of microstructure and pore systems, making feasibility analysis challenging. This study qualitatively and quantitatively investigates the Bowland shale microstructure in 3D at five length scales: artificial fractures at 10–100 mm scale, matrix fabric at 1–10 mm-scale, individual mineral grains and organic matter particles at 100 nm–1 mm scale, macropores and micro-cracks at 10–100 nm scale and organic matter and mineral pores at 1–10 nm-scale. For each feature, the volume fraction variations along the bedding normal orientation, the fractal dimensions and the degrees of anisotropy were analysed at all corresponding scales for a multi-scale heterogeneity analysis. The results are combined with other bulk laboratory measurements, including supercritical CO2 and CH4 adsorption at reservoir conditions, pressure-dependent permeability and nitrogen adsorption pore size distribution, to perform a comprehensive analysis on the storage space and flow pathways. A cross-scale pore size distribution, ranging from 2 nm to 3 mm, was calculated with quantified microstructure. The cumulative porosity is calculated to be 8%. The cumulative surface area is 17.6 m2 g1 . A model of CH4 and CO2 flow pathways and storage with quantified microstructure is presented and discussed. The feasibility of simultaneously enhanced gas recovery and subsurface CO2 storage in Bowland shale, the largest shale gas potential formation in the UK, was assessed based using multi-scale microstructure analysis. The potential is estimated to store 19.0–21.2 Gt CO2 as free molecules, together with 18.3–28.5 Gt CO2 adsorbed onto pore surfaces, implying a theoretical maximum of 47.5–49.5 Gt carbon storage in the current estimate of 38 trillion cubic metres (B1300 trillion cubic feet) of Bowland shale. Simple estimates suggest 6.0–15.8 Gt CO2 may be stored in practice

Variability in spatial distribution of mineral phases in the Lower Bowland Shale, UK, from the mm- to μm-scale: quantitative characterization and modelling

The microstructure of a highly laminated Lower Bowland Shale sample is characterized at the micron-to millimeter scale, to investigate how such characterization can be utilized for microstructure-based modelling of the shale's geomechanical behavior. A mosaic of scanning electron microscope (SEM) back-scattered electron (BSE) images was studied. Mineral and organic content and their anisotropy vary between laminae, with a high variability in fracturing and multi-micrometer aggregates of feldspars, carbonates, quartz and organics. The different microstructural interface types and heterogeneities were located and quantified, demonstrating the microstructural complexity of the Bowland Shale, and defining possible pathways for fracture propagation. A combination of counting-box, dispersion, covariance and 2D mapping approaches were used to determine that the total surface of each lamina is 3 to 11 times larger than the scale of heterogeneities relative to mineral proportion and size. The dispersion approach seems to be the preferential technique for determining the representative elementary area (REA) of phase area fraction for these highly heterogeneous large samples, supported by 2D quantitative mapping of the same parameter. Representative microstructural models were developed using Voronoï tessellation using these characteristic scales. These models encapsulate the microstructural features required to simulate fluid flow through these porous Bowland Shales at the mesoscale

Structural relaxation in a system of dumbbell molecules

The interaction-site-density-fluctuation correlators, the dipole-relaxation functions, and the mean-squared displacements of a system of symmetric dumbbells of fused hard spheres are calculated for two representative elongations of the molecules within the mode-coupling theory for the evolution of glassy dynamics. For large elongations, universal relaxation laws for states near the glass transition are valid for parameters and time intervals similar to the ones found for the hard-sphere system. Rotation-translation coupling leads to an enlarged crossover interval for the mean-squared displacement of the constituent atoms between the end of the von Schweidler regime and the beginning of the diffusion process. For small elongations, the superposition principle for the reorientational $\alpha$-process is violated for parameters and time intervals of interest for data analysis, and there is a strong breaking of the coupling of the $\alpha$-relaxation scale for the diffusion process with that for representative density fluctuations and for dipole reorientations.Comment: 15 pages, 14 figures, Phys. Rev. E in pres

An efficient semiparametric maxima estimator of the extremal index

The extremal index $\theta$, a measure of the degree of local dependence in the extremes of a stationary process, plays an important role in extreme value analyses. We estimate $\theta$ semiparametrically, using the relationship between the distribution of block maxima and the marginal distribution of a process to define a semiparametric model. We show that these semiparametric estimators are simpler and substantially more efficient than their parametric counterparts. We seek to improve efficiency further using maxima over sliding blocks. A simulation study shows that the semiparametric estimators are competitive with the leading estimators. An application to sea-surge heights combines inferences about $\theta$ with a standard extreme value analysis of block maxima to estimate marginal quantiles.Comment: 17 pages, 7 figures. Minor edits made to version 1 prior to journal publication. The final publication is available at Springer via http://dx.doi.org/10.1007/s10687-015-0221-

Amelioration of bleomycin-induced lung fibrosis in hamsters by dietary supplementation with taurine and niacin: biochemical mechanisms.

Interstitial pulmonary fibrosis induced by intratracheal instillation of bleomycin (BL) involves an excess production of reactive oxygen species, unavailability of adequate levels of NAD and ATP to repair the injured pulmonary epithelium, and an overexuberant lung collagen reactivity followed by deposition of highly cross-linked mature collagen fibrils resistant to enzymatic degradation. In the present study, we have demonstrated that dietary supplementation with taurine and niacin offered almost complete protection against the lung fibrosis in a multidose BL hamster model. The mechanisms for the protective effect of taurine and niacin are multifaceted. These include the ability of taurine to scavenge HOCl and stabilize the biomembrane; niacin's ability to replenish the BL-induced depletion of NAD and ATP; and the combined effect of taurine and niacin to suppress all aspects of BL-induced increases in the lung collagen reactivity, a hallmark of interstitial pulmonary fibrosis. It was concluded from the data presented at this Conference that the combined treatment with taurine and niacin, which offers a multipronged approach, will have great therapeutic potential in the intervention of the development of chemically induced interstitial lung fibrosis in animals and humans

Computing Fresnel integrals via modified trapezium rules

In this paper we propose methods for computing Fresnel integrals based on truncated trapezium rule approximations to integrals on the real line, these trapezium rules modified to take into account poles of the integrand near the real axis. Our starting point is a method for computation of the error function of complex argument due to Matta and Reichel (J Math Phys 34:298–307, 1956) and Hunter and Regan (Math Comp 26:539–541, 1972). We construct approximations which we prove are exponentially convergent as a function of N , the number of quadrature points, obtaining explicit error bounds which show that accuracies of 10−15 uniformly on the real line are achieved with N=12 , this confirmed by computations. The approximations we obtain are attractive, additionally, in that they maintain small relative errors for small and large argument, are analytic on the real axis (echoing the analyticity of the Fresnel integrals), and are straightforward to implement