Seminars Archive

Preferred orientation and elastic anisotropy of shales investigated with synchrotron X-ray diffraction

Abstract
Shales and mudstones comprise over half of the rocks in sedimentary basins, and are the main seals of hydrocarbon reservoirs and have thus received a lot of interest. One property of shales is their high velocity anisotropy that is significant for seismic prospecting. Anisotropy is mainly due to the alignment of minerals that is attained during sedimentation, compaction and secondary deformation. Shales are composed of many phases with extremely complex diffraction patterns. The development of the texture analysis with the Rietveld method on hard X-ray synchrotron diffraction images permits to quantify preferred orientation (texture) of mineral phases in shales, and it has been successfully used in a range of different materials. Here a complete analysis of an example of Jurassic Opalinus Clay from Mont Terri (Switzerland), that is being investigated in the context of radioactive waste disposal, is illustrated and compared with different samples. From texture patterns we can model polycrystal elastic properties by averaging over the orientation distribution. Data for predicted acoustic velocities can then be compared with experiments where velocities have been measured in a multianvil pressure apparatus.