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Continuum‐scale models used to model and predict two‐phase flow in the subsurface are often based on averaged flow parameters and do not consider pore‐scale fluid flow phenomena, for example, ganglion dynamics and thin‐film flow. As such, a major challenge in upscaling two‐phase flow for groundwater engineering applications is understanding the impact of disconnected flow and ganglion dynamics on continuum‐scale flow functions such as relative permeability‐saturation and capillary pressure‐saturation curves. In this study, we explored how changes in wettability and fluid velocity affect ganglion dynamics. We conducted pore‐scale numerical simulations with OpenFOAM to investigate the displacement of decane by water. Additionally, we examined how displaced phase saturation (a continuum‐scale flow function) responds to changes in dynamic fluid connectivity. We identified three different fluid flow regimes, that is, the connected pathway flow regime, ganglion dynamics (GD) flow regime, and droplet traffic flow regime, and studied the effects of changes in the wettability of the porous medium and the velocity of the invading fluid on the transitions between these different regimes. Our research showed that transitions between connected and disconnected pore‐scale flow regimes, which are induced by changes in fluid velocity and wettability, have a significant impact on both fluid displacement efficiency and average fluid flow transport kinetics. Plain Language Summary: The transport and confinement of hydrocarbons, organic pollutants or carbon dioxide (CO2) within rock pores is a complicated process that occurs on a minuscule scale and is crucial to groundwater engineering activities. The interplay of intricate fluid dynamics and alterations in rock and fluid characteristics at the microscopic level can have a considerable influence on continuum‐scale flow properties. Continuum‐scale models used to predict fluid flow in the subsurface are usually based on averaged flow parameters and do not account for the physics that occur at the pore scale. This often leads to disparities between the flow predictions made at the pore scale and at the field scale. A long‐standing challenge in scaling up flow from the pore scale to the continuum scale lies in addressing the impact of disconnected fluid ganglia and ganglion dynamics on overall flow transport kinetics. This work aims to bridge this gap between the pore and continuum scales. We investigate the behavioral response of the saturation function (a continuum‐scale function) to wettability and flow rate‐induced changes in dynamic fluid connectivity. Key Points: Changes in wettability and fluid flow rate induce transitions between connected and disconnected pore‐scale flow regimesTransitions between pore‐scale flow regimes have significant effects on the saturation function and flow transport kineticsThe Lomeland, Ebeltoft, and Thomas (L‐E‐T) relative permeability model can capture the effects of pore‐scale changes in fluid connectivity [ABSTRACT FROM AUTHOR]

Usually, models describing flow and transport for sub‐surface engineering processes at the Darcy‐scale do not take into consideration the effects of pore‐scale flow regimes and fluid connectivity on average flow functions. In this article, we investigate the impact of wettability on pore‐scale flow regimes. We show that fluid connectivity at the pore scale has a significant impact on average flow kinetics and therefore its contribution should not be ignored. Immiscible two‐phase flow simulations were performed in a two‐dimensional model of a Berea sandstone rock for wettability conditions ranging from moderately water‐wet to strongly oil‐wet. The simulation results show that wettability has a strong impact on invading fluid phase connectivity, which subsequently influences flow transport resistance. The effect of invading‐phase connectivity and ganglion dynamics (GD) on two‐phase displacement kinetics was also investigated. It was found that invading phase connectivity decreases away from the neutrally wet (intermediate wet) state. This study provides evidence that GD accelerate fluid flow transport kinetics during immiscible displacement processes. Lastly, the impact of wettability on fluid displacement efficiency and residual saturations was investigated. Maximum displacement efficiency occurred at the neutrally wet state. Key Points: The dominance of ganglion dynamics increases as the wettability shifts away from the neutrally wet stateGanglion dynamics accelerate displacement kinetics and reduce resistance to transport of the invading phaseFluid displacement efficiency increases as the connected pathway flow regime becomes more dominant [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]