Underground hydrogen storage (UHS) in porous reservoirs offers a promising solution for addressing the temporal and spatial variability of renewable energy sources. To safely and efficiently utilize these reservoirs for UHS at an affordable cost, it is essential to understand the diverse disciplines involved at various scales. This study combines large-scale techno-economic evaluations with micro- scale laboratory research to assess the commercial and technical viability of UHS in porous media. A techno-economic case study of commercial-scale UHS in a depleted gas field in the Dutch nearshore is investigated, defining the integrated scope of infrastructure and facilities and estimating associated costs. Additionally, the multiphase flow behavior and redistribution of hydrogen in sandstone rock are analyzed through experimental assessment of relative permeability, capillary trapping, dissolution, and Ostwald ripening using CT imagery. The case study compares various surface facility design concepts, revealing that the Levelized Cost of Hydrogen Storage (LCOHS)
ranges from [cannot be disclosed for confidentiality reasons] , depending on the required purification scope of the production stream. Cushion gas cost significantly impacts the LCOHS. The multiphase flow behavior was examined on a micro-scale by co-injecting hydrogen and brine at varying fractional flows into a vertically placed 17 cm Berea sandstone rock sample at 25°C and 50 bar, while observing under CT imaging during both drainage and imbibition. High- resolution CT imaging visualized Ostwald ripening at the pore scale after several periods without flow. The experimental results indicate a hydrogen end-point relative permeability of 0.043 and a linear trapping coefficient of 0.725. No preferential flow paths were observed, however, dissolution was shown to have an impact the saturation profiles. Pore-scale image analysis demonstrated that Ostwald ripening leads to the fragmentation of mid-sized hydrogen ganglia and the growth of larger ganglia over time. These findings provide valuable insights into optimizing UHS and provide input for large-scale reservoir simulations, emphasizing the importance of integrating techno-economic assessments with detailed laboratory research for the commercial success of UHS.