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.