Measuring intergranular force in granular media

A new method is proposed to measure intergranular forces in granular geomaterial from time-lapsehigh-resolution X-ray computed tomographyimaging using a grain trackingapproachand discrete element metho

Elucidating the Structure and Composition of Individual Bimetallic Nanoparticles in Supported Catalysts by Atom Probe Tomography

Understanding and controlling the structure and composition of nanoparticles in supported metal catalysts are crucial to improve chemical processes. For this, atom probe tomography (APT) is a unique tool, as it allows for spatially resolved three-dimensional chemical imaging of materials with sub-nanometer resolution. However, thus far APT has not been applied for mesoporous oxide-supported metal catalyst materials, due to the size and number of pores resulting in sample fracture during experiments. To overcome these issues, we developed a high-pressure resin impregnation strategy and showcased the applicability to high-porous supported Pd-Ni-based catalyst materials, which are active in CO2 hydrogenation. Within the reconstructed volume of 3 × 105 nm3, we identified over 400 Pd-Ni clusters, with compositions ranging from 0 to 16 atom % Pd and a size distribution of 2.6 ± 1.6 nm. These results illustrate that APT is capable of quantitatively assessing the size, composition, and metal distribution for a large number of nanoparticles at the sub-nm scale in industrial catalysts. Furthermore, we showcase that metal segregation occurred predominately between nanoparticles, shedding light on the mechanism of metal segregation. We envision that the presented methodology expands the capabilities of APT to investigate porous functional nanomaterials, including but not limited to solid catalysts

Micro-XCT images, grain size distributions and mechanical data used in: "Uniaxial compaction of sand using 4D X-ray tomography: The effect of mineralogy on grain-scale compaction mechanisms."

The mechanical behaviour of sand aggregates is often studied as a proxy for poorly consolidated sands and highly porous sandstones. Only recently research aimed at understanding sand deformation has started to use techniques that allow for direct observation of the in-situ grain-scale processes. Using state-of-the-art, time-lapse micro X-ray computed tomography (micro-XCT) imaging, the influence of mineralogy on the compaction of sand aggregates has been investigated by performing uniaxial compaction experiments on four different mineral assemblies (quartz, K-feldspar, quartz + K-feldspar and quartz + K-feldspar + clay) at room temperature and dry conditions. For the experiments, a bespoke uniaxial compaction device (sample diameter 2 mm) was constructed and coupled with micro-XCT imaging. This enabled in-situ observation of the strain-accommodating processes during deformation. To verify that the microstructural evolution observed in the small-scale experiments is representative for larger aggregate behaviour, conventional, centimetre-sized, control experiments were performed. The observed inelastic deformation was mainly accommodated by processes such as intragranular cracking and intergranular sliding. At low axial stresses (10 MPa), grain fracturing mainly occurred in K-feldspar grains, if present, along cleavage planes. Only at higher axial stresses, fracturing of quartz grains, if present, was also observed. Presence of clays, in pores and grain contacts, delayed the onset of quartz grain breakage and enhanced porosity reduction as clay in grain contacts facilitated grain sliding and rearrangement. The data provided in this dataset include all micro-XCT images, the grain size distributions determined using a Malvern Instruments Mastersizer S long bed particle sizer, the grain size distributions determined based on the micro-XCT images, and the mechanical data obtained in uniaxial compaction tests on pure quartz, pure feldspar, a mixture of quartz and feldspar, and a mixture of quartz, feldspar and clay material. The mechanical data illustrates the stresses and strains during small-scale experiments which were imaged using X-ray tomography. All scans on which the manuscript is based are provided as a series of .tif-images which together form the 3D micro-XCT data

Micromechanics of High-Pressure Compaction in Granular Quartz Aggregates

The mechanical behavior of porous sandstones is generally modeled using concepts from granular mechanics, often overlooking the effect of cementation. To probe the key differences between sand and sandstone mechanics, we performed triaxial deformation experiments on Ottawa quartz sand at 5- to 40 MPa effective confining pressure. At 5 MPa, the samples are able to dilate. At higher confinement, the aggregates show continuous compaction, displaying strain hardening. The stress-strain behavior is nonlinear, and the exact onset of inelastic compaction could not be determined accurately. Measured P-wave velocities show the development of anisotropy. With increasing axial strain, the along-axis velocities tend to increase, while velocities perpendicular to the compression axis tend to decrease (at low pressure) or remain constant (at high pressure). In samples deformed under elevated pressure conditions, acoustic emission event locations are diffuse. Microstructural investigations show an increase in grain chipping and crushing with increasing confining pressure, but no evidence of localized compaction could be observed. The nature of the pore fluid, either decane or water, does not significantly influence the mechanical behavior at strain rates of 10−6 to 10−4 s−1. Grain angularity and grain-size distribution also did not significantly change the mechanical behavior. We infer that our observations indicate that the lack of cementation introduces additional degrees of freedom for grains to slide, rotate, and reorganize at the sample scale, precluding the existence and sustainability of stress concentrations beyond the grain scale. This results in progressive compaction and hardening, and lack of compaction localization

Micromechanics of High-Pressure Compaction in Granular Quartz Aggregates

The mechanical behavior of porous sandstones is generally modeled using concepts from granular mechanics, often overlooking the effect of cementation. To probe the key differences between sand and sandstone mechanics, we performed triaxial deformation experiments on Ottawa quartz sand at 5- to 40 MPa effective confining pressure. At 5 MPa, the samples are able to dilate. At higher confinement, the aggregates show continuous compaction, displaying strain hardening. The stress-strain behavior is nonlinear, and the exact onset of inelastic compaction could not be determined accurately. Measured P-wave velocities show the development of anisotropy. With increasing axial strain, the along-axis velocities tend to increase, while velocities perpendicular to the compression axis tend to decrease (at low pressure) or remain constant (at high pressure). In samples deformed under elevated pressure conditions, acoustic emission event locations are diffuse. Microstructural investigations show an increase in grain chipping and crushing with increasing confining pressure, but no evidence of localized compaction could be observed. The nature of the pore fluid, either decane or water, does not significantly influence the mechanical behavior at strain rates of 10−6 to 10−4 s−1. Grain angularity and grain-size distribution also did not significantly change the mechanical behavior. We infer that our observations indicate that the lack of cementation introduces additional degrees of freedom for grains to slide, rotate, and reorganize at the sample scale, precluding the existence and sustainability of stress concentrations beyond the grain scale. This results in progressive compaction and hardening, and lack of compaction localization

Micromechanics of High-Pressure Compaction in Granular Quartz Aggregates

The mechanical behavior of porous sandstones is generally modeled using concepts from granular mechanics, often overlooking the effect of cementation. To probe the key differences between sand and sandstone mechanics, we performed triaxial deformation experiments on Ottawa quartz sand at 5- to 40 MPa effective confining pressure. At 5 MPa, the samples are able to dilate. At higher confinement, the aggregates show continuous compaction, displaying strain hardening. The stress-strain behavior is nonlinear, and the exact onset of inelastic compaction could not be determined accurately. Measured P-wave velocities show the development of anisotropy. With increasing axial strain, the along-axis velocities tend to increase, while velocities perpendicular to the compression axis tend to decrease (at low pressure) or remain constant (at high pressure). In samples deformed under elevated pressure conditions, acoustic emission event locations are diffuse. Microstructural investigations show an increase in grain chipping and crushing with increasing confining pressure, but no evidence of localized compaction could be observed. The nature of the pore fluid, either decane or water, does not significantly influence the mechanical behavior at strain rates of 10−6 to 10−4 s−1. Grain angularity and grain-size distribution also did not significantly change the mechanical behavior. We infer that our observations indicate that the lack of cementation introduces additional degrees of freedom for grains to slide, rotate, and reorganize at the sample scale, precluding the existence and sustainability of stress concentrations beyond the grain scale. This results in progressive compaction and hardening, and lack of compaction localization

Geochemical interactions between hydraulic fracturing fluid and fractured Whitby Mudstone

We examine how a mechanically-induced fracture network may influence geochemical reaction between shale and stimulation fluid used in hydraulic fracturing. Two different types of bedding-parallel fractures, a simple fracture between bedding planes and a damage zone with multiple fractures, were induced in the Whitby Mudstone (Early Jurassic) from the UK. Both fractured shales were subsequently reacted with stimulation fluid at 10 MPa and 100°C for about 2000 hours. pH increased from 2.1 to about 6 after 1000 hours of reaction in both shales, but pH increased slightly more rapidly by reaction in the shale with the damage zone. Total dissolved inorganic carbon evolved in similar fashion in both experiments and did not readily distinguish between the two styles of fracturing induced in the Whitby Mudstone

Geochemical interactions between hydraulic fracturing fluid and fractured Whitby Mudstone

We examine how a mechanically-induced fracture network may influence geochemical reaction between shale and stimulation fluid used in hydraulic fracturing. Two different types of bedding-parallel fractures, a simple fracture between bedding planes and a damage zone with multiple fractures, were induced in the Whitby Mudstone (Early Jurassic) from the UK. Both fractured shales were subsequently reacted with stimulation fluid at 10 MPa and 100°C for about 2000 hours. pH increased from 2.1 to about 6 after 1000 hours of reaction in both shales, but pH increased slightly more rapidly by reaction in the shale with the damage zone. Total dissolved inorganic carbon evolved in similar fashion in both experiments and did not readily distinguish between the two styles of fracturing induced in the Whitby Mudstone

New approaches in experimental research on rock and fault behaviour in the Groningen gas field

This paper describes a research programme recently initiated at Utrecht University that aims to contribute new, fundamental physical understanding and quantitative descriptions of rock and fault behaviour needed to advance understanding of reservoir compaction and fault behaviour in the context of induced seismicity and subsidence in the Groningen gas field. The NAM-funded programme involves experimental rock and fault mechanics work, microscale observational studies to determine the processes that control reservoir rock deformation and fault slip, modelling and experimental work aimed at establishing upscaling rules between laboratory and field scales, and geomechanical modelling of fault rupture and earthquake generation at the reservoir scale. Here, we focus on describing the programme and its intended contribution to understanding the response of the Groningen field to gas production. The key knowledge gaps that drive the programme are discussed and the approaches employed to address them are highlighted. Some of the first results emerging from the work in progress are also reported briefly and are providing important new insights