Reactive transport modeling at the pore scale and upscaling to the Darcy scale
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Author
Date
2022Type
- Doctoral Thesis
ETH Bibliography
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Abstract
Reactive transport processes are fundamental for a large number of applications. At the millimeter--centimeter scale, reactive transport controls the electrolysis in rechargeable batteries, the dendritic growth in lithium-ion batteries, separation processes in chromatographic columns, and the corrosion of steel in concrete structures. At the meter--kilometer scale, reactive transport is relevant for geothermal energy extraction, geologic carbon sequestration, radioactive waste disposal, rock weathering, hydraulic stimulation, the remediation of contaminated sites, and the in-situ leaching of minerals. Therefore, developing reactive transport models is beneficial for understanding and predicting the behavior of reactive systems. Using geothermal energy utilization as an example, what would happen after the heat is extracted from the brine? Will the dissolved minerals precipitate and clog up the pipes? When we use supercritical CO2 as the working fluid, what will happen to the subsurface? Will the porosity or permeability of the reservoir change due to mineral reactions? Such questions can be addressed using reactive transport modeling. The main problems in developing a useful model for subsurface reactive transport are the large spatial and time scale differences between our understanding of reaction kinetics established in the lab and the application in the field. The reaction kinetics of minerals at the temperature and pressure conditions of a geothermal reservoir can also be hard to determine. Furthermore, detailed small-scale information relevant to reactive transport processes cannot be realized using geological modeling and geophysical methods. To contribute to our knowledge of field-scale reactive transport processes, the first part of the thesis focuses on the connection between mineral dissolution processes at the pore and the averaged spatial scale. I established a relationship between dissolution kinetics at these two scales using the reaction order. In addition, I developed a method for a flow-through experiment with which the pore-scale heterogeneity of a sample of porous medium can be assessed using the outlet/inlet concentrations of dissolved minerals. The second part of the thesis is dedicated to modeling the coulombic effects among ionic species in aqueous solutions. Such effects are also known as electromigration and are relevant in tight geological formations such as shale or clay, where the pores are on the scale of sub-micrometers. In these tiny pores, the coulombic effects are particularly relevant since the transport is primarily diffusion-controlled. Referring to results of lab-scale reactive flow experiments performed in a Hele-Shaw cell, I show that the coulombic effects can be essential when modeling reactive transport processes. Finally, I conclude the thesis with a summary and with perspectives. I discuss further research opportunities using the validated reactive transport model. One tangible result of this doctoral work is a modelling tool for reactive transport, RetroPy, which is freely available to the research community. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000585564Publication status
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Publisher
ETH ZurichOrganisational unit
09494 - Saar, Martin O. / Saar, Martin O.
Funding
175673 - Analysing spatial scaling effects in mineral reaction rates in porous media with a hybrid numerical model (SNF)
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Is supplemented by: https://doi.org/10.3929/ethz-b-000579224
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