Abstract
Understanding transport phenomena and governing mechanisms of different physical and chemical processes in porous media has been a critical research area for decades. Correlating fluid flow behaviour at the micro-scale with macro-scale parameters, such as relative permeability and capillary pressure, is key to understanding the processes governing subsurface systems, and this in turn allows us to improve the accuracy of modelling and simulations of transport phenomena at a large scale. Over the last two decades, there have been significant developments in our understanding of pore-scale processes and modelling of complex underground systems. Microfluidic devices (micromodels) and imaging techniques, as facilitators to link experimental observations to simulation, have greatly contributed to these achievements. Although several reviews exist covering separately advances in one of these two areas, we present here a detailed review integrating recent advances and applications in both micromodels and imaging techniques. This includes a comprehensive analysis of critical aspects of fabrication techniques of micromodels, and the most recent advances such as embedding fibre optic sensors in micromodels for research applications. To complete the analysis of visualization techniques, we have thoroughly reviewed the most applicable imaging techniques in the area of geoscience and geo-energy. Moreover, the integration of microfluidic devices and imaging techniques was highlighted as appropriate. In this review, we focus particularly on four prominent yet very wide application areas, namely “fluid flow in porous media”, “flow in heterogeneous rocks and fractures”, “reactive transport, solute and colloid transport”, and finally “porous media characterization”. In summary, this review provides an in-depth analysis of micromodels and imaging techniques that can help to guide future research in the in-situ visualization of fluid flow in porous media.
Highlights
Porous media contain a complex network of interconnected pores that allow fluids to flow through a porous medium
Reactive ion etching (RIE) is a ‘dry etching’ technology in which a material is selectively removed from the material surface by a chemically reactive plasma that is generated under low pressure is a limited number of pore network patterns than can be achieved with glass beads
The chemical, mechanical and thermal properties of micromodels should satisfy the requirements of experimental studies
Summary
Porous media contain a complex network of interconnected pores that allow fluids to flow through a porous medium. These devices have found use in geoscience, hydrogeology, petroleum and geo-energy engineering research to conduct experimental investigations of various processes occurring in porous media These physical micromodels contain an artificial structure of interconnected pores whose shapes are designed in such a way to represent simplified geometries of geomaterials, such as rocks and core plugs. The following section provides an in-depth analysis of the different types of microfluidic devices manufactured from a wide range of materials to replicate internal structures of various geomaterials This includes the review of various fabrication techniques (i.e., methods used for the generation and enclosure of pore network patterns), as well as a critical analysis of the advantages and limitations for each method. Highly-transparent High stiffness Direct laser writing enables rapid prototyping of micromodels Highly-transparent High stiffness Resistant to acids & solvents
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