Precipitation flow in a confined geometry: Mixing, fingering, and deposition

Abstract

Reactive flow in porous media, leading to solid precipitation and deposition, is a fundamental process with widespread implications across various fields, such as carbonate mineralization during CO2 sequestration process. Despite the extensive research on the precipitation flow, the physical mechanisms behind the coupling between the hydrodynamics and reaction are less well-understood. This thesis investigates the complex interplay between fluid flow and a chemical reaction (A+B=C) that triggers precipitation and deposition in a Hele-Shaw cell with a gap thickness much smaller than the ones used in the past. We find that both electrostatic and hydrodynamic forces influence the onset of fingering. The results reveal that precipitation-induced fingering plays a significant role in altering mixing dynamics and precipitation rate. A model is developed, incorporating a more realistic rheology model and a first-order deposition term into an advection-diffusion-reaction framework, to comprehensively analyze the impact of critical parameters such as injection rate and initial reactant concentrations on hydrodynamic instability resulting from precipitation and deposition. Validation against experimental data demonstrates the model's capability to capture diverse precipitation patterns observed under varying experimental conditions accurately. Additionally, the results highlight the crucial role of the deposition term in accurately predicting the temporal evolution of total solid content observed in the experiments. Furthermore, the thesis explores the influence of porous media heterogeneity on calcium carbonate mineralization dynamics in a 2D radial porous system. Using a flow cell with a bimodal pore throat size distribution, the study investigates the temporal evolution of the mixing front, total precipitation amount, and spatial distribution of deposited particles under different injection rates and reactant concentrations. Findings reveal the formation of stable mixing fronts at higher injection rates, driven by the creation of large aggregates, and demonstrate enhanced precipitation in porous media dominated by advection. Conversely, in diffusion-dominated conditions, the precipitation rate transitions to scaling behaviors observed in a homogeneous media. The experimental observations elucidate the deposition of large aggregates in low-permeability regions, leading to significant alterations in cell permeability and porosity.