Periodic Reporting for period 3 - PRD-Trigger (Precipitation triggered rock dynamics: the missing mesoscopic link)
Période du rapport: 2023-02-01 au 2024-07-31
Climate change leads to increasing weathering cycles on landscapes and the built environment. Promotion of alternative energy sources such as geothermal energy, or underground CO2 storage, intensifies cyclic perturbations of the underground environment. Both lead to precipitation-dissolution cycles of salts, natural constituents of brines present inside porous rock. When precipitation occurs inside the pores, stresses build up which eventually crack the material, and thus degrade the rocks’ structure. This might be a positive outcome, e.g. increasing the production rate of a geothermal reservoir or underground storage capacity, or, on the contrary, be the cause of severe deterioration of natural building stones and coastal erosion.
What triggers rock dynamics up to fracturing during salt precipitation? Can we ultimately control, and thus engineer, this trigger? The ERC Starting Grant project “Precipitation triggered rock dynamics: the missing mesoscopic link” (PRD-Trigger) advocates that the answer lies at the mesoscale, this is, the scale of the pore network of the rock. Specifically, it will combine 4D X-ray micro-tomographic imaging with a mesoscopic numerical simulator integrated into the image analysis workflow to identify and hierarchize key factors in precipitation-induced damage. By acting on the identified trigger(s), damage control and crack healing will then be demonstrated on core-scale rocks. These advanced methods could be used to increase durability of building stones, for protection of coastal areas and historic stone-buildings, as well as to optimize geoengineering of the subsurface.
What triggers rock dynamics up to fracturing during salt precipitation? Can we ultimately control, and thus engineer, this trigger? The ERC Starting Grant project “Precipitation triggered rock dynamics: the missing mesoscopic link” (PRD-Trigger) advocates that the answer lies at the mesoscale, this is, the scale of the pore network of the rock. Specifically, it will combine 4D X-ray micro-tomographic imaging with a mesoscopic numerical simulator integrated into the image analysis workflow to identify and hierarchize key factors in precipitation-induced damage. By acting on the identified trigger(s), damage control and crack healing will then be demonstrated on core-scale rocks. These advanced methods could be used to increase durability of building stones, for protection of coastal areas and historic stone-buildings, as well as to optimize geoengineering of the subsurface.
During the first reporting period, research focused on dynamic precipitation experiments in rocks to identify key correlations between morphological identifiers of the pore space (pore size, shape, connectivity), fluid and salt distributions and precipitation-induced damage, based on quantitative image processing of in-situ 4D X-ray micro-computed tomography experiments. A customized image analysis workflow is being established merging morphological recognition, phase segmentation and digital volume correlation. An optimal salt accumulation protocol has been defined to prepare samples that are subsequently prone to salt damage when being weathered in the X-ray scanner. A test cell is being finalized for controlling temperature, confining pressure, flow rate and gauge pressure in order to perform salt weathering flow-through experiments in the X-ray scanner. During the coming year, this will provide unique datasets on simultaneous transport, salt precipitation and mechanics in millimetric-sized rock samples.
The PRD-Trigger team aims to establish a robust framework at the pore-scale of rock material that will enable unravelling the trigger(s) for precipitation-induced rock dynamics. Therefore, the true coupling between local heat and mass transfer, local precipitation and pressures, and local deformations, which constitute the overall mechanical response of a rock, need to be revealed. These novel physical insights will open ways of defining protocols to regulate a rock’s mechanical and permeability response to precipitation or dissolution reactions by controlling the relevant governing processes.