Enzymatically Induced Calcite Precipitation (EICP) in porous media can be used as an engineering option to achieve targeted precipitation in the pore space, e.g. with the aim to seal flow paths. This is accomplished through an alteration of porosity and, consequently, permeability. A major source of uncertainty in modelling EICP is in the quantitative description of permeability alteration due to precipitation. This study investigates experimentally the time-resolved effects of growing precipitates on porosity and permeability on the pore scale in a PDMS-based micro-fluidic flow cell. The experimental methods are explained; these include the design and construction of the micro-fluidic cells, the preparation and usage of the chemical solutions, including the injection strategy, and the monitoring of pressure drops at given flux rates to conclude on permeability. Imaging methods are explained with application to EICP, including optical microscopy and X-Ray micro-Computed Tomography (XRCT) and the corresponding image processing and analysis. We present and discuss detailed experimental results for one particular micro-fluidic set-up as well as the general perspectives for further experimental and numerical simulation studies on induced calcite precipitation. The results of the study show the enormous benefits and insights of combining both light microscopy and XRCT with hydraulic measurements in micro-fluidic devices. This allows for a quantitative analysis of the evolution of precipitates with respect to their size and shape, while monitoring the influence on permeability. We can demonstrate that we improved the interpretation of monitored flow data dependent on changes in pore morphology.

Employing kinetic interface sensitive (KIS) tracers, we investigate three different types of glass-bead materials and two natural porous media systems to quantitatively characterize the influence of the porous-medium grain-, pore-size, and texture on the “mobile” interfacial area between an organic liquid and water. By interpreting the breakthrough curves (BTCs) of the reaction product of the KIS tracer hydrolysis we obtain a relationship for the specific interfacial area (IFA) and wetting saturation. The immiscible displacement process coupled with the reactive tracer transport across the fluid-fluid interface is simulated with a Darcy-scale numerical model. The results show that the current reactive transport model is not always capable to reproduce the breakthrough curves of tracer experiments and that a new theoretical framework is required. Total solid surface area of the grains, i.e., grain surface roughness, is shown to have an important influence on the capillary-associated IFA by comparing results obtained from experiments with spherical glass beads having very small or even no surface roughness and those obtained from experiments with the natural sand. Furthermore, a linear relationship between the mobile capillary associated IFA and the inverse mean grain diameter can be established. The results are compared with the data collected from literature measured with high-resolution microtomography and partitioning tracer methods. The capillary associated IFA values are consistently smaller because KIS tracers measure the mobile part of the interface. Through this study, the applicability range of the KIS tracers is considerably expanded and the confidence in the robustness of the method is improved.

Previous laboratory experiments with KIS tracers have shown promising results with respect to the quantification of fluid-fluid interfacial area (IFA) for dynamic, two-phase flow conditions. However, pore-scale effects relevant for two-phase flow (e.g. the formation of hydrodynamically stagnant/ immobile zones) are not yet fully understood, and quantitative information in how far these effects influence the transport of the tracer reaction products is not yet available. Therefore, a pore-scale numerical model that includes two-phase, reactive flow and transport of the KIS tracer at the fluid-fluid interface is developed. We propose a new method to quantitatively analyze how the concentration of the KIS-tracer reaction product in the effluent is affected by the presence of immobile zones. The model employs the phase field method (PFM) and a new continuous mass transfer formulation, consistent with the PFM. We verify the model with the analytical solution of a reaction-diffusion process for two-phase flow conditions in a conceptual capillary tube. The applicability of the model is demonstrated in NAPL/water drainage scenarios in a conceptual porous domain, comparing the results in terms of the spatial distribution of the phases and the quantified macro-scale parameters (saturation, capillary pressure, IFA and solute concentration). Furthermore, we distinguish the mobile and immobile zones based on the local Péclet number, and the corresponding solute mass in these two zones is quantified. Finally, we show that the outflow concentration can be employed to selectively determine the mobile part of the IFA.