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The challenge of characterizing subsurface fluid flow has motivated extensive laboratory studies, yet fluid flow through rock specimens in which fractures are created and maintained at high‐stress conditions remains underinvestigated at this time. The studies of this type that do exist do not include in situ fracture geometry measurements acquired at stressed conditions, which would be beneficial for interpreting the flow behavior. Therefore, this study investigates the apparent permeability induced by direct‐shear fracture stimulation through Utica shale (a shale gas resource and potential caprock material) at high triaxial stress confinement and for the first time relates these values to simultaneously acquired in situ X‐ray radiography and microtomography images. Change in fracture geometry and apparent permeability was also investigated at additional reduced stress states. Finite element and combined finite‐discrete element modeling were used to evaluate the in situ observed fracturing process. Results from this study indicate that the increase in apparent permeability through fractures created at high‐stress (22.2 MPa) was minimal relative to the intact rock (less than 1 order of magnitude increase), while fractures created at low stress (3.4 MPa) were significantly more permeable (2 to 4 orders of magnitude increase). This study demonstrates the benefit of in situ X‐ray observation coupled with apparent permeability measurement to analyze fracture creation in the subsurface. Our results show that the permeability induced by fractures through shale at high stress can be minor and therefore favorable in application to CO2 sequestration caprock integrity but unfavorable for hydrocarbon recovery from unconventional reservoirs.

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This article describes the effect of fabrication conditions on as-sintered microstructures of various stoichiometric ratios of uranium dioxide, UO 2 + x , with the aim of enhancing the understanding of the fabrication process and developing and validating a predictive microstructure-based model for fuel performance. We demonstrate the ability of novel, non-destructive methods such as near-field highenergy X-ray diffraction microscopy (nf-HEDM) and micro-computed tomography (μ-CT) to probe bulk samples of high-Z materials by non-destructively characterizing three samples: UO 2.00 , UO 2.11 , and UO 2.16 , which were sintered at 1450°C for 4 hours. The measured 3D microstructures revealed that grain size and porosity were influenced by deviation from stoichiometry.

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