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The utilization of depleted natural gas reservoirs is a significant consideration for large-scale hydrogen (H₂) storage and production. However, accurate knowledge of cushion gas compositions such as nitrogen (N₂), methane (CH₄), and carbon dioxide (CO₂) is crucial, as they are critical components that affect the rock-fluid interfacial phenomenon, thereby impacting deployment feasibility. Moreover, there are limited reported studies on rock/brine/gas-mixture wettability and gas-mixture/brine surface tension for this type of reservoir. To address this gap, we explore the possibility of using N₂ as a cushion gas (in the presence of CH₄ and CO₂) on a pristine quartz for H₂ storage across various pressure (500–3000) psi, temperature (30–70) °C, and salinity (2–20) wt.%. We conducted extensive contact angle (CA) and surface tension (ST) experiments for different gas mixtures (H₂–N₂–CH₄–CO₂) to generate relevant …