Browsing by Author "Vahid Dastjerdi, Samaneh"

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Open Access
Experimental evaluation of fluid connectivity in two‐phase flow in porous media during drainage
(2022) Vahid Dastjerdi, Samaneh; Karadimitriou, Nikolaos; Hassanizadeh, S. Majid; Steeb, Holger
This study aims to experimentally investigate the possibility of combining two extended continuum theories for two‐phase flow. One of these theories considers interfacial area as a separate state variable, and the other explicitly discriminates between connected and disconnected phases. This combination enhances our potential to effectively model the apparent hysteresis, which generally dominates two‐phase flow. Using optical microscopy, we perform microfluidic experiments in quasi‐2D artificial porous media for various cyclic displacement processes and boundary conditions. Specifically for a number of sequential drainage processes, with detailed image (post‐)processing, pore‐scale parameters such as the interfacial area between the phases (wetting, non‐wetting, and solid), and local capillary pressure, as well as macroscopic parameters like saturation, are estimated. We show that discriminating between connected and disconnected clusters and the concept of the interfacial area as a separate state variable can be an appropriate way of modeling hysteresis in a two‐phase flow scheme. The drainage datasets of capillary pressure, saturation, and specific interfacial area, are plotted as a surface, given by f (Pc, sw, awn) = 0. These surfaces accommodate all data points within a reasonable experimental error, irrespective of the boundary conditions, as long as the corresponding liquid is connected to its inlet. However, this concept also shows signs of reduced efficiency as a modeling approach in datasets gathered through combining experiments with higher volumetric fluxes. We attribute this observation to the effect of the porous medium geometry on the phase distribution. This yields further elaboration, in which this speculation is thoroughly studied and analyzed.
Open Access
Experimental methods and imaging for enzymatically induced calcite precipitation in a microfluidic cell
(2021) Weinhardt, Felix; Class, Holger; Vahid Dastjerdi, Samaneh; Karadimitriou, Nikolaos; Lee, Dongwon; Steeb, Holger
Enzymatically induced calcite precipitation (EICP) in porous media can be used as an engineering option to achieve precipitation in the pore space, for example, aiming at a targeted sealing of existing flow paths. This is accomplished through a porosity and consequent permeability alteration. A major source of uncertainty in modeling EICP is in the quantitative description of permeability alteration due to precipitation. This report presents methods for investigating experimentally the time‐resolved effects of growing precipitates on porosity and permeability on the pore scale, in a poly‐di‐methyl‐siloxane microfluidic flow cell. These methods include the design and production of the microfluidic cells, the preparation and usage of the chemical solutions, the injection strategy, and the monitoring of pressure drops for given fluxes for the determination of permeability. EICP imaging methods are explained, including optical microscopy and X‐ray microcomputed tomography (XRCT), and the corresponding image processing and analysis. We present and discuss a new experimental procedure using a microfluidic cell, as well as the general perspectives for further experimental and numerical simulation studies on induced calcite precipitation. The results of this study show the enormous benefits and insights achieved by combining both light microscopy and XRCT with hydraulic measurements in microfluidic chips. This allows for a quantitative analysis of the evolution of precipitates with respect to their size and shape, while monitoring their influence on permeability. We consider this to be an improvement of the existing methods in the literature regarding the interpretation of recorded data (pressure, flux, and visualization) during pore morphology alteration.
Open Access
Image-based characterization of multiphase flow in porous media
(Stuttgart : Institute of Applied Mechanics, 2024) Vahid Dastjerdi, Samaneh; Steeb, Holger (Prof. Dr.-Ing.)
Multiphase flow in porous media encompasses a wide range of applications, including groundwater management, resource extraction, and carbon dioxide sequestration. This interdisciplinary field intersects geophysics, hydrology, and environmental science and has the potential to revolutionize industrial applications. The dynamics of imbibition and drainage processes in porous media and the relevant underlying physics, as well as developing effective models to describe them, are among the main focuses of research in multiphase porous media flow. This work primarily revolves around equations to compute capillary pressure and accommodate features like hysteresis. To follow this aim, experimental observations are examined by integrating two continuum theories for phase flow in porous media. One theory extends the understanding of multiphase flow by incorporating essential elements in thermodynamic equations, namely phases, and their interfaces, formulating capillary pressure as a function of saturation and phases' specific interfacial area. The fact that interfaces are the locus of force exchange between all the present phases supports the necessity of considering them in describing a multiphase flow system. The other theory addresses limitations in conventional approaches by differentiating between percolating and non-percolating fluid clusters. This theory employs the fact that the distribution of forces is different in the percolating and non-percolating fluid elements. This research merges these theories to enhance the available comprehension of two-phase flow in porous media. In order to collect the pore-scale information necessary as the input parameters in the mentioned continuum theories, microfluidic experiments are carried out and visualized using a customized open-air microscope. The high-resolution recording of experiments provides real-time information on the two-phase flow process. Subsequently, the recorded snapshots are processed via a self-developed segmentation and parameter calculation code. The REV-scale parameters gathered from the experiments, among others, include saturation and specific interfacial area. The results from the experiments show that an approach that considers specific interfacial area when differentiating between percolating and non-percolating fluid elements proves valuable in modeling two-phase porous media flow. Moreover, a linear relation between saturation and specific interfacial area of percolating fluid phases is observed, which could help find more efficient models for multiphase fluid flow in a porous medium. Additionally, the formation of preferential flow paths after cyclic phase displacements is documented. These preferential flow paths, referred to as an effective porous medium, remain unaltered when enough fluid clusters are stranded. The stranded fluid clusters and the solid matrix form the effective porous medium, which constrains the flow to the preferential flow pathways for both fluids, regardless of the wetting properties of the flow system. This observation highlights the need to differentiate between primary and scanning events in applications. These results could contribute to advancing a two-phase flow theory capable of capturing dynamic conditions and hysteresis phenomena, emphasizing the importance of considering interfacial area and phase connectivity in continuum theories.
Open Access
Spatiotemporal distribution of precipitates and mineral phase transition during biomineralization affect porosity-permeability relationships
(2022) Weinhardt, Felix; Deng, Jingxuan; Hommel, Johannes; Vahid Dastjerdi, Samaneh; Gerlach, Robin; Steeb, Holger; Class, Holger
Enzymatically induced calcium carbonate precipitation is a promising geotechnique with the potential, for example, to seal leakage pathways in the subsurface or to stabilize soils. Precipitation of calcium carbonate in a porous medium reduces the porosity and, consequently, the permeability. With pseudo-2D microfluidic experiments, including pressure monitoring and, for visualization, optical microscopy and X-ray computed tomography, pore-space alterations were reliably related to corresponding hydraulic responses. The study comprises six experiments with two different pore structures, a simple, quasi-1D structure, and a 2D structure. Using a continuous injection strategy with either constant or step-wise reduced flow rates, we identified key mechanisms that significantly influence the relationship between porosity and permeability. In the quasi-1D structure, the location of precipitates is more relevant to the hydraulic response (pressure gradients) than the overall porosity change. In the quasi-2D structure, this is different, because flow can bypass locally clogged regions, thus leading to steadier porosity-permeability relationships. Moreover, in quasi-2D systems, during continuous injection, preferential flow paths can evolve and remain open. Classical porosity-permeability power-law relationships with constant exponents cannot adequately describe this phenomenon. We furthermore observed coexistence and transformation of different polymorphs of calcium carbonate, namely amorphous calcium carbonate, vaterite, and calcite and discuss their influence on the observed development of preferential flow paths. This has so far not been accounted for in the state-of-the-art approaches for porosity–permeability relationships during calcium carbonate precipitation in porous media.