Characterizing Low-Permeable Granitic Rock from Micrometer to Centimeter Scale: X-ray Microcomputed Tomography, Confocal Laser Scanning Microscopy and ¹⁴C-PMMA Method

Abstract

First results of combining X-ray microcomputer tomography (µCT), confocal laser-scanning microscopy (CLSM) and 14C-polymethylmethacrylate (14C-PMMA) impregnation techniques in the study of granitic rock samples are reported. Combining results of µCT and CLSM with those of the 14C-PMMA technique, the mineral-specific porosity and morphology of the open pore space, as well as its connectivity, could be analyzed from a micrometer up to a decimeter scale.

Three different types of granite were studied. In two cases part of the micro-fissure and pore apertures were found to be in a micrometer scale, but in one case all grain-boundary openings were below the detection limit. Micrometer-scale apertures could be analyzed by CLSM and µCT. The benefit of µCT is that it can also provide the heterogeneous distribution of minerals in 3D. The 2D porosity distributions in the mineral phases, consisting of nanometer-scale pores, could be measured by the 14C-PMMA method together with the micro-fissures. This method does not, however, give the exact pore apertures. The limitations and applicability of the methods are discussed.