Confocal scanning laser microscopy applied to the study of pore and crack networks in rocks

Confocal scanning laser microscopy (CSLM) is a powerful tool to image the t hree-dimensional (3D) microstructure of objects in many different fields. T he goal of this paper is to show that, in particular, confocal microscopy i s a useful tool in geosciences because it provides accurate and relevant in formation on the 3D geometry of the pore space in rocks. Three important ge ological processes have been investigated: cracking in granites, cementatio n and diagenetic compaction in sandstones and hydrothermal alteration in gr anular materials. CSLM was used to characterise 3D crack networks in La Pey ratte granite samples in which cracking was artificially induced either by heating samples at selected temperatures in order to induce thermal crackin g, or by performing mechanical tests in order to develop stress-induced cra cking at room temperature. Qualitative and quantitative results show the di fferent mechanisms acting during natural cracking. CSLM was also used to st udy the natural cementation of sediments; for this purpose 3D observations of the pore system of Fontainebleau sandstone samples with different degree s of cementation and diagenesis were done. We found large differences in co nnectivity, pore size and shape depending on cementation. Finally, we prese nt some results on artificial granular materials (sintered glass beads) alt ered by hot water (220 degreesC): some microstructural parameters were anal ysed in order to quantify the effect of alteration on the microstructural p roperties of the granular material. We concluded from this study that the l arge drop in permeability (6 orders of magnitude), when comparing non-alter ed to altered samples, is due to a complete change of the pore structure an d a strong reduction of the mean pore size. (C) 2001 Elsevier Science Ltd. All rights reserved.