This study explores the potential of repurposing depleted natural gas reservoirs for green hydrogen storage, utilizing the material balance equation (MBE) framework. The presence of an aquifer, a common feature in many depleted reservoirs, is considered, and the Carter and Tracy aquifer model is applied alongside the Peng-Robinson equation of state for hydrogen. A case study is conducted using a reference reservoir geometry with varying hydraulic properties (porosity and permeability) and a range of natural gas production rates. Results indicate that natural gas production rate, formation permeability, and porosity are critical factors not only for gas extraction but also for determining the feasibility of hydrogen storage. The study finds that typical sandstone reservoirs are most suitable for hydrogen storage, while formations with very high or low permeability present challenges. The findings highlight that with appropriate reservoir management, depleted gas reservoirs could serve as an effective hydrogen storage solution, contributing to a more flexible and resilient energy system. Future research should focus on understanding biochemical reactions in these reservoirs when exposed to hydrogen, which remains a relatively unexplored area.