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Salt Crystallization in Porous Media is a critical phenomenon found in various natural processes and applications, such as the degradation of built structures, gas recovery and storage, and underground CO₂ storage. This phenomenon impacts the petrophysical properties of rocks, particularly porosity and permeability, fundamental parameters in the description of fluid flow in porous media. The reduction of permeability due to salt crystallization is typically estimated in reservoir simulators by means of empirical relationships. However, the validity of these relationship is not always guaranteed, and precise experimental data on the link between salt crystallization and permeability is scarce.
We developed an experimental protocol promoting, as much as possible, a homogeneous distribution of salt crystals at the scale of the representative elementary volume (REV), enabling a reliable assessment of their impact on permeability. We therefore propose an experimental approach based on vacuum drying. We conducted successive cycles of saturation with a potassium chloride saline solution, followed by vacuum drying, on various artificial porous media samples with different pore sizes (VitraPOR cylinders, 6 mm diameter, pore sizes between 40-100 µm, 100-160 µm, 160-250 µm, 250-500 µm). These cycles were repeated until a maximum amount of salt was reached within the porous medium. At each step, X-ray tomography scans were performed to quantify and visualize salt deposits, alongside weight measurements to compare the amounts of precipitated salt. After each cycle, the permeability was measured experimentally by placing the confined sample in a Hassler cell and measuring the pressure drop over the sample while injecting an inert fluid at a controlled rate.
The results of this study demonstrate that vacuum drying allows for a homogeneous distribution of salt crystals within the pore network, with a progressive accumulation of salt after each cycle as precipitation primarily remains in the same locations (Figure 1). Such homogeneity was not achieved using conventional drying methods, which tend to induce heterogeneous crystallization, primarily at the sample edges, making it difficult to establish an accurate experimental relationship between permeability and salt quantity. Successive permeability measurements enabled us to establish an experimental curve linking permeability to the deposited salt mass. These findings provide a promising avenue for improving and refining the modeling of physical phenomena involving salt crystallization in porous media. Future perspectives of this study include expanding the experiments to different types of natural rocks, such as Savonnières limestone and Bentheimer sandstone, as well as using a more commonly encountered salt in various application domains where this phenomenon occurs, namely NaCl.
Acknowledgements: The authors acknowledge the support from the ERC Starting Grant PRD-Trigger (grant agreement N° 850853), the Fédération de Recherche IPRA (FR CNRS-UPPA 2952), and the Research Foundation Flanders (FWO, G004820N).
| Country | France |
|---|---|
| Water & Porous Media Focused Abstracts | This abstract is related to Water |
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