Many physical processes in the field of rock physics are influenced by the presence of fractures and microcracks. Therefore, intact rock samples are often used for reproducible experimental studies, and cracks are artificially created by various methods. For this, one possibility is the use of thermal treatments. In this work, twelve thermal treatments, differing in the applied maximum temperature and the applied cooling condition (slow versus fast cooling) are experimentally studied for dry Bianco Carrara marble under ambient conditions. Two sizes of cylindrical core samples are investigated to identify a potential size effect. As effective quantities on the core-scale, the bulk volume, the bulk density, and the P- and S-wave velocities, including shear wave splitting, are examined. To obtain a three-dimensional insight into the mechanisms occurring on the micro-scale level, micro X-Ray Computed Tomography (micro-XRCT) imaging is employed. For both cooling conditions, with increasing maximum temperature, the bulk volume increases, and the propagation velocities significantly drop. This behavior is amplified for fast cooling. The bulk volume increase is related to the initiated crack volume as micro-XRCT shows. Based on comprehensive measurements, a logarithmic relationship between the relative bulk volume change and the relative change of the ultrasound velocities can be observed. Although there is a size effect for fast cooling, the relationship found is independent of the sample size. Also the cooling protocol has almost no influence. A model is derived which predicts the relative change of the ultrasound velocities depending on the initiated relative bulk volume change.

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.

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.