Impact of mixing-driven precipitation and sharp soil interfaces on solute transport: from laboratory visualization to numerical modeling
(English) Understanding the dynamics of solute transport in highly heterogeneous porous systems represents an inherent challenge for assessing various subsurface activities, such as carbon sequestration and groundwater remediation. This difficulty arises from the inability to directly observe the pr...
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| Tipo de recurso: | tesis doctoral |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/440633 |
| Acceso en línea: | https://hdl.handle.net/2117/440633 https://dx.doi.org/10.5821/dissertation-2117-440633 |
| Access Level: | acceso embargado |
| Palabra clave: | solute transport mixing porous media heterogeneity mixing-driven precipitation (MDP) sharp soil interfaces geological carbon sequestration (GCS) groundwater remediation laboratory experiment numerical modeling 624 - Enginyeria civil i de la construcció en general 55 - Geologia. Meteorologia Àrees temàtiques de la UPC::Enginyeria civil |
| Sumario: | (English) Understanding the dynamics of solute transport in highly heterogeneous porous systems represents an inherent challenge for assessing various subsurface activities, such as carbon sequestration and groundwater remediation. This difficulty arises from the inability to directly observe the processes occurring in the subsurface. To improve the understanding of the impact of heterogeneity on solute transport, it is crucial to visualize and evaluate these processes in well-controlled experimental settings. The objective of this thesis is to enhance the current understanding of the impact of heterogeneity on solute transport dynamics through laboratory experiments and numerical modeling. The work offers new experimental insights into solute transport, mixing, and chemical reactions in highly heterogeneous porous media, with a particular focus on the role of mineral precipitation and sharp soil interfaces in transport dynamics, aiming to enhance the conceptual and numerical understanding of these complex processes. The first part of the thesis investigates the impact of Mixing-Driven Calcite Precipitation (MDP) on solute transport. Laboratory experiments were conducted in an intermediate-scale Hele-Shaw cell, simulating a coarse-sand porous medium to observe the spatiotemporal evolution of calcite precipitation under mixing conditions. Self-organized heterogeneities in the precipitate structure were observed, with calcite layers forming symmetric patterns aligned with the main flow, contrasting with the asymmetry predicted by a semi-analytical model under idealized conditions. Tracer tests conducted before and after precipitation demonstrated significant impacts on solute transport, including the emergence of strong anomalous transport features, such as earlier solute arrival, a distinct double peak, and pronounced tailing. The thesis continues with a chapter that evaluates how self-organized heterogeneous porous media, induced by mineral precipitation, should be characterized in a solute transport model to effectively reproduce the resulting non-Fickian transport behavior. To achieve this, we analyze the spatial variability of hydraulic conductivity by implementing different permeability scenarios in a random walk particle tracking model. Our results highlight the importance of capturing two key features to effectively describe solute transport. First, delineating the total precipitated area is crucial for accurately representing flow diversion caused by permeability reduction, which explains the emergence of the double peak in solute concentrations. However, fully capturing both the double peak transition and tailing requires representing the internal structure of the high-precipitation zones within the precipitated area, as these characterize internal preferential flow channels. The thesis concludes with an experimental work that investigates the impact of sharp interfaces in reactive and conservative solute transport. Experiments were conducted in an intermediate-scale horizontal tank to visualize and evaluate the spatiotemporal evolution of solutes plumes. The results show that the reaction product encounters anomalous resistance when crossing the interface between coarse and fine materials. This effect is less pronounced during the fine-to-coarse (FC) transition. An unexpected enhancement of the transverse spread of the reaction product is observed in the coarse-to-fine (CF) transition, accompanied by a slower release within the fine material. A sudden decrease in the longitudinal resident concentration is detected across the heterogeneity interface. Mixing metrics reveal that, as the apparent transverse dispersivity increases near the interface during the CF transition, both the scalar dissipation rate and the total mass reacted also rise, indicating greater solute reactivity compared to the FC configuration. |
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