EarthFlow: Unravelling the spatio-temporal nature of rock deformation using 4D X-ray tomography
Talk by François Renard (ISTerre, Univ. Grenoble Alpes & PGP, UiO) in relation with the EarthFlow project, but addressed to a broad audience.
Examples of 3D X-ray tomography imaging of microstructures and deformations in rocks. a) Microfractures in a shale rock [Kobchenko et al., 2011]. b) Hydraulic fracture in a limestone [Renard et al., 2009]. c) Fracturing by salt damage into a sandstone [Noiriel et al., 2010]. d) View of a grain of carbonate with pressure solution creep indentations. e) View of fossil burrows in a shale. f) Views of melt at grain boundaries into a peridotite rock [Zhu et al., 2011].
The rocks of the Earth’s crust deform in diverse environments such as fault zones, volcanoes, geological reservoirs, sedimentary basins, mountain ranges, and oceanic crust. These deformations, either brittle (i.e. fracturing) or ductile (i.e. creep) play a major role in the release of the internal energy of the planet and control the transport of fluids between its deepest parts to the surface. As such, they also play a key role in the formation, migration, and trapping of underground georesources and the sustainability of long term waste storage in geological repositories.
The development of high resolution 3D microtomography imaging, using laboratory X-ray tomographs or synchrotron sources, now allows one to scan rock samples, without destroying them, at higher and higher resolutions, down to 0.1 micron, and shorter acquisition durations, down to a fraction of a second (Figure 1). With this technique, some difficulties of observing deformation under thermodynamic conditions relevant for geodynamic processes are overcome: rocks can be deformed and heated actually inside the X-ray beam with the result that one can watch them evolve live in 3D and time. In the next years, in PGP, we will develop a novel rock 'see through' deformation triaxial rig coupled to X-ray microtomography at the ESRF and 3D numerical models, to answer the following scientific questions:
- How do fracturing and creep mechanisms interact in rocks and control rupture nucleation?
- How does deformation couple with fluid flow in fractures and porous rocks?
- How do phase transformations in rocks induce fracturing?