Characterization of pore-space heterogeneity in sandstone by X-ray computed tomography

Abstract

Abstract In this study we review some of the recent advances in the application of X-ray computed tomography (X-ray CT) to geomaterials. This non-destructive technique based on density contrasts provides 2D images comparable with micrographs and 3D reconstructions at various resolutions depending on the acquisition setup. Synchrotron images with resolution of a few microns allow for 3D mapping of the pore space and can be used to perform 3D fluid flow simulations. ‘Industrial’ CT systems can provide images of centimetre-sized samples with a resolution of c . 50 µm. This resolution is suitable for studying centimetre-scale structural heterogeneities and compaction localization, as illustrated in recent studies. Starting from images taken at both synchrotron and industrial resolutions in intact samples of porous sandstones, we show that important conclusions on pore-space heterogeneity can be drawn from global and local analysis of the distributions of X-ray attenuation values. The global analysis is used in particular to identify relatively homogeneous materials in which compaction bands are likely to develop. Local analysis performed over small clusters of voxels appears to have more potential for the geometric description of the pore space. We show the existence of a resolution at which the local coefficient of variation of the X-ray distributions reaches a maximum. This resolution, which is about an order of magnitude lower than synchrotron resolution, appears to be related to the pore size, and the corresponding coefficient of variation to the porosity.