Subsurface processes play a crucial role in determining the efficiency and viability of key applications with significant technical and economic implications, including hydrocarbon production, CO₂/H₂ geo-storage, and environmental engineering. A comprehensive understanding of natural behavior including microstructures, morphologies, and various petrophysical properties at pore scale is vital for optimizing the utilization of underground energy storage formations. Despite ongoing efforts, the behavior of diverse natural phenomena in the subsurface remains inadequately understood. This work leverages imaging techniques in conjunction with flow displacement experiments in investigating various natural phenomena, such as CO₂/H₂ geo-sequestration and fracture propagation. Additionally, the significance of microfluidic experiments in studying the dynamics of multiphase flows are briefly underscored. As a conclusion, porous media characterisation at pore scale is valuable for the advance in the understanding of natural phenomenon in subsurface engineering and the subsurface sciences, and upscaling them across space and time.

Traditional correlation analyses based on whole-rock data have limitations in discerning pore development determinants in shale oil reservoir, given the complex lithology of shale formations and intricate interdependencies (multicollinearity) among geological variables. In this study, mercury injection capillary pressure and digital analysis of scanning electron microscopy were employed to examine the macropore structures of both whole rocks and their constituent lithologies for the Upper Triassic Chang-7 shale of the Ordos Basin. Variations were observed among clay shale (shale primarily consisting of clay-sized mineral grains), massive siltstone and silty laminae within the Chang-7 shale. Through the combination of correlation analysis and scanning electron microscope digital technique, it was demonstrated that total organic carbon content primarily controls the level of macropore development, while lithology primarily governs macropore types and structures. Although quartz and pyrite exhibit correlations with macropore volume, they do not emerge as primary factors; instead, they appear interconnected to total organic carbon. Due to detrital mineral framework preservation during compaction, larger macropores are more developed in massive siltstones and silty laminae than in clay shale. Additionally, silty laminae, situated closer to the source rock and influenced by organic acids, exhibit a higher abundance of larger dissolution pores, potentially favoring shale oil development. This study overcomes traditional method constraints, disentangling multi-correlations, and providing new insights into shale macropore development mechanisms, potentially advancing shale oil exploration and production.

With the advent of X-ray micro-computed tomography which is now routinely used, pore-scale fluid transport and processes can be observed in three-dimensional (3D) at the micro-scale. Multiphase flow experiments that are conducted under $i\mathrm{}n\mathrm{}s\mathrm{}i\mathrm{}t\mathrm{}u$ imaging scanning conditions can be utilized to study the pore-scale physics relevant to subsurface technological applications. X-ray micro-tomographic imaging is a non-destructive technique for quantifying these processes in 3D within confined pores. This paper presents a review for the usage of X-ray micro-computed tomography experiments to investigate wettability effect on multiphase flow. The fundamental workflow of combining experiments with pore-scale $i\mathrm{}n\mathrm{}s\mathrm{}i\mathrm{}t\mathrm{}u$ imaging scanning such as equipment requirements, apparatus design and fluid systems are firstly described. Then imaging analysis toolkit is presented for how to quantify interfacial areas, curvatures, contact angles, and fluid properties through these images. Furthermore, we show typical examples, illustrating recent studies for the wettability characterization by using X-ray micro-computed imaging.