EXPLORING THE HYDROMECHANICS OF A HETEROGENEOUS POROUS SANDSTONE: COUPLED IN SITU EXPERIMENTS WITH X-RAY AND NEUTRON IMAGING

In geoengineering, such as oil and gas production, geological CO2 storage, geothermal projects, and environmental remediation, a detailed understanding of the hydraulic and mechanical properties of sandstone properties is crucial. Traditional theories on the hydraulic and mechanical behavior of rocks rely on bulk measurements from boundary sensors, which fail to capture complex heterogeneity in structure and processes, such as localized deformation and sedimentary fabrics, leading to inaccurate predictions of fluid transport properties in geological systems. To address these limitations, full-field measurements using imaging techniques like X-ray and neutron tomography and Digital Image Correlation (DIC) can provide detailed insights into rock hydromechanics. These techniques not only reveal structural and deformation details but can also be used to track fluid movement during percolation tests. Combining different methods mitigates their individual limitations and enhances our understanding of sandstone hydromechanics. This thesis presents a combined experimental approach to characterize the hydromechanical behavior of porous rocks during triaxial-permeability tests, validated through two experimental campaigns at the NeXT instrument at Institut Laue-Langevin (ILL). Additionally, pre-Darcy flow was investigated using neutron radiography at the Neutra instrument at Paul Scherrer Institute (PSI). The thesis covers the entire development of the experimental cycle, from designing the experimental setup to developing image analysis algorithms and correlating full-field results with bulk measurements. The final chapter employs numerical modeling using the Finite Element Method to further elucidate experimental phenomena, creating digital replicas of the tests with analogous boundary conditions and full-field sample properties from the images. The experimental setup, imaging analysis tool, and numerical modeling in this thesis provide new insights into the hydromechanical behavior of porous granular rocks. Specifically, the evolution of both local and bulk permeability under deformation, the role of porosity in strain development and localization, and the variation in permeability with flow rate in undeformed samples are discussed.