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Experimental study of reactive transport in porous media : application to dissolution coupled with density gradients

Abstract : Predicting the instabilities triggered by the chemical reaction of a percolating fluid passing through soluble rock is a major scientific challenge for many fields of application (formation of karstic systems, fracture evolution, acid stimulation of oil wells or CO2 sequestration and storage). Indeed, the dissolution of the solid matrix often leads to the appearance and development of channels, called wormholes, which modify the hydrodynamic characteristics (permeability and porosity) of the crossed medium. The objective of this thesis is to study, through an experimental laboratory program, the influence of the variation of the physical properties of the percolating fluid and in particular the variation of its density on the configuration of the wormholes. In other words, the coupling between chemical and hydrodynamic instabilities induced by density contrast is studied. In a first step, the experimental program is based on the interpretation of images acquired during the injection of pure water ("acid" phase) in a saline massif ("soluble" rock) reconstituted in 2D via a Hele-Shaw type cell and considering different injection configurations. In a second step, the use of X-ray tomography allowed to approach these effects in a 3D configuration consisting of specimens of salts dissolved by under-saturated salt solutions. Whatever the studied configuration, the experimental results suggest that the dissolution regimes can still be described by the two classical adimensional numbers, namely the Damköhler and Péclet numbers. The regime diagram is not very sensitive to variations in density contrast, especially for relatively strong Péclet and weak Damköhler numbers, but suffers a slowing down of the propagation of the dissolution front when the Richardson number (ratio of gravitational and convective effects) increases. The analysis of morphological descriptors such as volume, dissolved/undissolved zone interface, tortuosity and pore size distribution shows that the density contrast has a non-negligible influence on the dissolution regimes for medium to strong Richardson. Some of our experimental results were confirmed by two-dimensional numerical simulations conducted with COMSOL Multiphysics® software.
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Submitted on : Wednesday, February 24, 2021 - 11:28:11 AM
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Assohoun Ahoulou. Experimental study of reactive transport in porous media : application to dissolution coupled with density gradients. Hydrology. Université de Lorraine, 2020. English. ⟨NNT : 2020LORR0172⟩. ⟨tel-03150910⟩



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