Grains, grids and mineral surfaces: approaches to grain-scale matrix modeling based on X-ray micro-computed tomography data

Abstract

X-ray micro-computed tomography (X-μCT) generates 3D mineral distribution maps currently with a resolution of about 10 μm. For tight crystalline rocks, this implies that the mineral grains are well resolved, while micro-fractures, having apertures of less than 10 μm, are not resolved. In this study, we propose a method to analyze the properties (size, volume, surface area) of the mineral grains based on X-μCT data. The numerical approach uses a resolution similar to that of the X-μCT data and hence shares the same limitations. For example, it is clear that a large fraction of the mineral surface area is due to so-called roughness, with scales below 10 μm. In the second part of the study, methods to generate the diffusion-available pore space are discussed. The inter-granular space (distance between grains) is often smaller than 10 μm, and we need to design methods to be able to perform diffusion simulations in the matrix. Three methods, all based on X-μCT, are discussed, and it is demonstrated that models with realistic global properties (mean porosity and effective diffusion coefficient) can be developed based on the suggested techniques.

STED nanoscopy – A novel way to image the pore space of geological materials

“…STED high‐resolution fluorescence microscopy might be beneficial to support recent developments of grain‐scale matrix transport modelling by confirming model assumptions and giving direct input data. Indeed, the use of pore‐scale direct numerical modelling of flow and reactive transport needs an accurate description of microscale rock matrix properties, in particular, of intra‐ and intergranular pore surfaces, which is limited by the resolution of current X‐ray microcomputed tomography (X‐ray μ‐CT) presently to a scale of about 10 μm 56,57 …”