HR: 1330h
AN: T42A-0270    [PDF]
TI: A Close View Into the 3D Geometry of Grain-to-Grain Contacts and Surface Roughness in Sandstones Using Laser Scanning Confocal Microscopy
AU: Menendez, B
EM: beatriz.menendez@geol.u-cergy.fr
AF: UMR CNRS 7072 Univ. Cergy-Pontoise, Av.du Parc - Le Campus - Bat I, Cergy-Pontoise, 95031 France
AU: David, C
EM: christian.david@geol.u-cergy.fr
AF: UMR CNRS 7072 Univ. Cergy-Pontoise, Av.du Parc - Le Campus - Bat I, Cergy-Pontoise, 95031 France
AU: * Louis, L
EM: laurent.louis@geol.u-cergy.fr
AF: UMR CNRS 7072 Univ. Cergy-Pontoise, Av.du Parc - Le Campus - Bat I, Cergy-Pontoise, 95031 France
AU: Martinez Nistal, A
EM: angel@lupo.quimica.uniovi.es
AF: Universidad de Oviedo, Servicio de Proceso de Imagenes, Oviedo, 33006 Spain
AB: Due to its sharp resolution ($<$ 1 micron) and its ability in building 3D reconstructions from images scanned at various depths, laser scanning confocal microscopy (LSCM) is a powerful tool to render the three-dimensional geometry of microstructural features like pores, cracks and grains. This technique was used in particular to study the grain-to-grain contacts and grain surface topology at small scale in several sandstones. For that purpose, the rock samples to be studied were impregnated with a fluorescent dyed (Rhodamine B) resin in order to discriminate the void space from the grains. The next stage is then to make thin-sections with a thickness larger than usual ($>$ 100 microns) that can be studied under LSCM. Three different sandstones have been studied: the Rothbach sandstone (Vosges mountains, Eastern France), the Bentheim sandstone (Germany) and the Darley Dale sandstone (UK). On each sample several three dimensional blocks have been investigated with size 228 by 152 microns and depths ranging from 35 to 100 microns. From each block, series of tens of parallel "virtual sections" have been recorded, separated by 1 or 2 microns in depth. We show on several examples the complex structure of grain-to-grain contacts which may be associated to the heterogeneity in cement distribution. In particular for the Rothbach sandstone, we found that the topology of the grain surfaces is dominated by the coating of clay particles which leads to a high surface roughness. Complementary SEM studies revealed that the clays are also present as cementing material between the grains. A thorough petrophysical study has shown that the anisotropy of P wave velocity in the Rothbach sandstone can be explained by an anisotropic distribution of cement: whereas this could not be confirmed from our LSCM and SEM analysis, we observed that the spatial distribution of contact lengths is anisotropic which explains qualitatively the spatial variability of P wave velocity. Finally we show examples of Hertzian cracks that initiated from the contact between grains in Darley Dale sandstone samples that experienced mechanical loading under triaxial conditions.
DE: 5102 Acoustic properties
DE: 5112 Microstructure
SC: Tectonophysics [T]
MN: 2003 Fall Meeting