Unravelling the spatio-temporal nature of rock deformation using 4D X-ray tomography

Rocks in the 30 kilometers thick upper layer of the Earth, called the crust, deform slowly, for example during the formation of geological reservoirs, or very fast, for example during earthquakes. Such deformations control how voids and fractures are created underground and how fluids may circulate in rocks and transport hydrocarbons, heat (geothermal energy), or minerals that later deposit as ores. Here, we reproduce rock deformation processes, coupled to fluid circulations, using a state-of-the-art deformation apparatus that reproduces conditions of pressure, temperature, and fluid flow in a rock sample similar to that at 3 to 8 kilometers depth. This rig is installed at the European Synchrotron Radiation Facility in Grenoble (France), where high-energy X-rays are used, for the first time, to image in real-time the evolution of the rocks. One doctorate student has performed experiments with this unique deformation apparatus. One post-doctoral fellow has performed big data analysis (machine learning) and numerical simulations of the physical processes at work during the coupled fluid flow - deformation of the rocks. This project has involved collaboration between the Njord Centre at the University of Oslo, and internationally renowned researchers for the universities of Maryland, Utrecht, and Grenoble Alpes. A collaboration with a famous graphic artist from Norway enabled to develop new science-art interactions. New paintings are now exposed at UiO.

The new rock deformation apparatus, the Hades rig, installed at the European Synchrotron Radiation Facility has attracted a wide international attention. This apparatus is now copied and the technique is being developed on other synchrotrons (Soleil in Paris, Swiss Light Source, Advanced Photon Source in USA). The main results allowed to 1) image rock deformation processes in 4D with high time resolution, 2) develop new numerical methods to model rock deformations (discrete element models, machine learning), 3) train two early career female researchers, one of them has obtained a YFF grant (Jessica McBeck) and the other one should defend her PhD in 2020 (Neelima Kandula), 4) establish international collaborations with the Universities of Maryland and Utrecht and strengthen collaborations with the University Grenoble Alpes. Finally, the PI has submitted an ERC Advanced grant proposal in august 2020, based on results of the present FriPro project.

When rocks deform in the interior of the Earth and along plate boundaries, they release part of the internal energy of the planet. These deformations may be either brittle, for example during earthquakes, or ductile, for example in shear zones or during slow earthquakes. The search for precursors to brittle deformations and for the parameters that control the transition towards ductile processes in the presence of reactive fluids represents key challenges to be investigated in this project. A major difficulty in understanding many geodynamic processes is that they occur at depths where data and samples cannot be accessed directly. However, in specially designed laboratory experiments, it is now possible to reproduce the conditions and thus geodynamic processes occurring between 0 and 10 km depths. A triaxial rock deformation rig, the only one of its kind worldwide because it is see-through at such thermodynamic conditions, has been developed at the Univ. of Oslo, in collaboration with the European Synchrotron Radiation Facility (ESRF). Samples under pressure and temperature will be imaged in-situ using synchrotron X-ray tomography directly inside the rig at a spatial resolution down to 0.6 micrometer under a photon energy of 60 keV. This device is installed on the beamline ID19 at the ESRF, the only beamline in Europe where the necessary energy and spatial resolution can be reached. With this new apparatus, a major advance is expected in rock physics, and more generally in material sciences, with several international academic research groups engaged. We will use the 3D data acquired at different spatial resolution at the ESRF to search for aseismic precursors to rupture and simulate mechano-chemical processes where fluid flow and chemical reactions are coupled to deformation. These studies will be fundamental to search for the evolution of fluid transport properties in the Earth's crust and applications in the domain of geo-engineering will be also developed.