On the Role and Evolution of Local Grain Size Heterogeneity During Confined Compression of Boise Sandstone as Seen by X-ray Micro-CT Imaging

MicroCT imaging is performed before and after confined compression testing of a minicore of Boise sandstone to extract quantitative information on the microstructural controls on compaction initiation and distribution, and to test whether grain size distributions tend to conform to a power law through comminution. In contrast with traditional compaction studies, this analysis focuses on local statistics among regions of a given sample as opposed to global statistics in a sample set. The original workflow includes a segmentation strategy and the definition of a series of metrics that are evaluated throughout the entire image volumes before and after testing. The results suggest that local porosity and sorting are the main controls on local strength, whereas neighborhoods with larger mean grain size do not appear to be more prone to yielding. Furthermore, our observations appear to confirm the tendency of grain size distributions to become self-similar through the elimination of same size neighbors at all scales, consistent with the concept of fractal compression. The relationship between grain size statistics and the compaction process is studied by contrasting image-derived metrics among many sub-regions of a sandstone CT scan.Despite a large influence of the macroscopic stress distribution associated with the testing conditions, local metrics statistically provide meaningful insight.Porosity and sorting emerge as the main controls on local strength, whereas neighborhoods with larger mean grain size are not more prone to yielding.Upon grain microcracking and crushing, grain size distributions conform to power laws, consistent with geological observations and numerical simulations.This work provides a possible path to image-based prediction of compaction initiation and development in high porosity aggregates.