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Instruments / Technical Area	Publication Details	Published
I13-2-Diamond Manchester Imaging	Comparison of methods to segment variable-contrast XCT images of methane-bearing sand using U-nets trained on single dataset sub-volumes Fernando Alvarez-Borges , Oliver N. F. King , Bangalore N. Madhusudhan , Thomas Connolley , Mark Basham , Sharif I. Ahmed Methane 2, 1 - 23 DOI: 10.3390/methane2010001 Diamond Proposal Number(s): [16205] Open Access Show Abstract ▼ Abstract: Methane (CH4) hydrate dissociation and CH4 release are potential geohazards currently investigated using X-ray computed tomography (XCT). Image segmentation is an important data processing step for this type of research. However, it is often time consuming, computing resource-intensive, operator-dependent, and tailored for each XCT dataset due to differences in greyscale contrast. In this paper, an investigation is carried out using U-Nets, a class of Convolutional Neural Network, to segment synchrotron XCT images of CH4-bearing sand during hydrate formation, and extract porosity and CH4 gas saturation. Three U-Net deployments previously untried for this task are assessed: (1) a bespoke 3D hierarchical method, (2) a 2D multi-label, multi-axis method and (3) RootPainter, a 2D U-Net application with interactive corrections. U-Nets are trained using small, targeted hand-annotated datasets to reduce operator time. It was found that the segmentation accuracy of all three methods surpass mainstream watershed and thresholding techniques. Accuracy slightly reduces in low-contrast data, which affects volume fraction measurements, but errors are small compared with gravimetric methods. Moreover, U-Net models trained on low-contrast images can be used to segment higher-contrast datasets, without further training. This demonstrates model portability, which can expedite the segmentation of large datasets over short timespans.	Dec 2022
I12-JEEP: Joint Engineering, Environmental and Processing	Pore-scale imaging of hydrogen displacement and trapping in porous media Eike M. Thaysen , Ian B. Butler , Aliakbar Hassanpouryouzband , Damien Freitas , Fernando Alvarez-Borges , Samuel Krevor , Niklas Heinemann , Robert Atwood , Katriona Edlmann International Journal Of Hydrogen Energy 105 DOI: 10.1016/j.ijhydene.2022.10.153 Diamond Proposal Number(s): [26730] Open Access Show Abstract ▼ Abstract: Hydrogen can act as an energy store to balance supply and demand in the renewable energy sector. Hydrogen storage in subsurface porous media could deliver high storage capacities but the volume of recoverable hydrogen is unknown. We imaged the displacement and capillary trapping of hydrogen by brine in a Clashach sandstone core at 2–7 MPa pore fluid pressure using X-ray computed microtomography. Hydrogen saturation obtained during drainage at capillary numbers of <10−7 was ∼50% of the pore volume and independent of the pore fluid pressure. Hydrogen recovery during secondary imbibition at a capillary number of 2.4 × 10−6 systematically decreased with pressure, with 80%, 78% and 57% of the initial hydrogen recovered at 2, 5 and 7 MPa, respectively. Injection of brine at increasing capillary numbers up to 9.4 × 10−6 increased hydrogen recovery. Based on these results, we recommend more shallow, lower pressure sites for future hydrogen storage operations in porous media.	Nov 2022
I12-JEEP: Joint Engineering, Environmental and Processing	Correlative neutron and X-ray tomography imaging of pile installation in chalk Fernando Alvarez-Borges , Genoveva Burca , Robert Atwood , Andrew James , Mark Wolstenholme , Sharif Ahmed Géotechnique DOI: 10.1680/jgeot.21.00318 Diamond Proposal Number(s): [26232] Show Abstract ▼ Abstract: Neutron and X-ray tomography (NCT and XCT, respectively) are imaging techniques increasingly being applied in geomechanics research. They are used to non-destructively reveal different microstructural aspects of geomaterials: XCT is often used to observe/quantify differences in density or porosity, while NCT reveals the presence and distribution of hydrogenous materials such as water. The correlated use of NCT and XCT for geomechanics and geotechnics research is in its infancy. To this date, very few experiments have been carried out that combine both techniques, and none have been used to investigate geomaterial-structure interaction. This paper presents the first correlative NCT-XCT imaging study of pile installation. A scaled model pile was installed in an unsaturated intact chalk cylinder and in-situ NCT and ex-situ XCT synchrotron-based imaging was applied consecutively. Chalk was used because the behaviour of displacement piles installed in this material is still subject to considerable uncertainty. Results reveal for the first time the interaction between installation-induced changes in chalk density and water distribution variations, with evidence of water displacement into the densified material in the vicinity of the installed pile. A straightforward method for correlative bulk density-moisture content determination from NCT-XCT images of geomaterials are presented and their limitations discussed.	Jul 2022

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