Hydrogen-Methane Blend Storage in Depleted Reservoirs: An Option for Reusing Decommissioned Offshore Platforms

The paper presents an innovative approach to studying the reuse of a decommissioned natural gas production platform for the seasonal storage and extraction of a hydrogen-methane (H2-CH4) mixture from a depleted reservoir. The reuse plan involves removing outdated equipment from the platform’s decks while retaining essential components such as wellheads and separators. Exploiting a depleted reservoir for the injection of an H2-CH4 mixture requires a thorough understanding of its specific characteristics. This paper focuses on the engineering approach adopted in the basic design phase for such a conversion, providing recommendations and HSE guidelines. Given the hazardous nature of substances like hydrogen in the gas mixture, the paper also examines potential risk scenarios, particularly those involving containment loss. A qualitative and quantitative assessment of these risks is conducted to evaluate their impact on the structure and equipment. The results of this assessment serve as a foundation for later studies on layout optimization and domino effect prevention. Additionally, some critical scenarios are simulated using an innovative approach known as the Source Box Accident Model (SBAM), which was proposed in previous works. SBAM leverages Computational Fluid Dynamics (CFD) but decouples the accidental phenomenon into a release phase and a dispersion phase. This method overcomes the challenges conventional CFD tools face in assessing congested plant configurations, providing more precise estimations of gas cloud behavior. The simulation results indicate that the released gas remains within the platform deck domain, and the flammable cloud is significantly smaller than what traditional, simplified tools predict.