Multi-scale characterization of the hydromechanical behavior of a heterogeneous porous sandstone using neutron and X-ray tomographies

Understanding the hydromechanical behavior of porous media such as sandstones is critical to various geoengineering applications such as geologic carbon storage, geothermal projects, oil and gas production and environmental remediation in aquifers. In these contexts, accurate quantification of the constitutive hydromechanical behavior of sandstones is necessary to predict reservoir responses. In this work, neutron tomography data were acquired during coupled triaxial-flow tests on Idaho Gray sandstone cores to characterize the full-field hydromechanical response. The hydromechanical response was then correlated to macroscopic observations obtained at the sample boundaries and to the initial natural microstructural heterogeneity characterized using high-resolution X-ray tomography. The flow tests involved saturating samples with D₂O and performing volume-driven H₂O injection, with rapid (1-min) neutron in situ tomography. Digital volume correlation (DVC) on high-resolution neutron tomography data enabled tracking of 3D strain evolution describing the mechanical deformation. Neutron tomography data acquired during the permeability tests enabled 4D (3D + time) fluid flow analysis, revealing heterogeneous percolation paths. The comparison of the initial porosity and strain fields indicated that sample porosity heterogeneity influenced both strain evolution and shear band localization. Additionally, a relationship was identified between the evolution of the fluid flow field and the strain field. Notably, changes in percolation paths correlated with the evolution of the volumetric strain field.