Image-based characterization of multiphase flow in porous media

Abstract

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.