Conventional manufacturing of microfluidic devices from glass substrates is a complex, multi-step process that involves different fabrication techniques and tools. Hence, it is time-consuming and expensive, in particular for the prototyping of microfluidic devices in low quantities. This article describes a laser-based process that enables the rapid manufacturing of enclosed micro-structures by laser micromachining and microwelding of two 1.1-mm-thick borosilicate glass plates. The fabrication process was carried out only with a picosecond laser (Trumpf TruMicro 5×50) that was used for: (a) the generation of microfluidic patterns on glass, (b) the drilling of inlet/outlet ports into the material, and (c) the bonding of two glass plates together in order to enclose the laser-generated microstructures. Using this manufacturing approach, a fully-functional microfluidic device can be fabricated in less than two hours. Initial fluid flow experiments proved that the laser-generated microstructures are completely sealed; thus, they show a potential use in many industrial and scientific areas. This includes geological and petroleum engineering research, where such microfluidic devices can be used to investigate single-phase and multi-phase flow of various fluids (such as brine, oil, and CO2) in porous media.

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.

The physical process whereby an immiscible fluid phase replaces a second resident fluid in a porous medium is characteristic of many subsurface operations that include remediation of non-aqueous phase liquids (NAPLs), enhanced oil recovery (EOR), and carbon capture and storage (CCS) technology (Edery et al., 2018;Singh et al., 2017). Mobilization of residual NAPL and oil blobs and trapping of gas bubbles are critical to such operations (Geistlinger & Mohammadian, 2015).In CCS applications, the trapping of supercritical carbon dioxide in the interstitial spaces of porous rocks (known as capillary or residual trapping) inhibits plume migration and enhances storage safety and capacity (Al-Menhali et al., 2016;Krevor et al., 2015). Capillary trapping can contribute up to 40% of the overall CO 2 trapping in the first 100 years post-injection (Li et al., 2015), and it is strongly influenced by the wettability of the porous medium (

Carbon dioxide (CO2) emissions from power stations and industrial plants are seen as major contributors to what is known as the greenhouse gas (GHG) effect. Carbon dioxide capture and storage (CCS) is one technology which may reduce the quantity of CO2 released into the atmosphere but development of CCS has slowed due to the absence of a viable financial model. Metering technology is a prerequisite in enabling realistic financial decisions to be taken; however, there is currently a paucity of research into the types of flowmeters which would be suitable for incorporating into CCS transportation chains. This paper reviews and summarizes existing metering technologies with a view to establishing their suitability for measuring high mass flowrate, supercritical CO2. Open channel, differential pressure, velocity measurement, direct mass measurement, and electrical, magnetic, thermal, sonic, and radiation technologies are all considered. The challenges associated with each generic group are described, and recommendations made regarding the practicalities of using particular types of meter for CO2 transport in CCS applications. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.

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