Evaluating the Thermophysical Behaviours of H2–CH4 Mixtures for Underground Hydrogen Storage: Implications for Nigerian Gas Reservoirs

Underground hydrogen storage (UHS) has attracted a significant amount of interest in recent years due to the global demand for cleaner energy. It is a pivotal technology that can ensure the success of the energy transition, enabling large-scale renewable energy integration and decarbonisation through storage of hydrogen in the subsurface to balance demand and supply of hydrogen. This research investigates the phase behaviour and thermophysical properties of hydrogen when mixed with potential impurities in the subsurface. It analyses binary hydrogen gas mixtures with methane (CH4) under varying temperature and pressure conditions, with a focus on their applicability for underground hydrogen storage. A numerical model was developed using the GERG-2008 equation of state to evaluate critical properties such as density, viscosity, and heat capacity across a range of compositions. Possibly phase transitions were noticed as a certain P-T range. Machine learning techniques were employed by creating a pipeline, including linear regression, random forest, support vector regression, and decision tree regression, to predict key properties such as viscosity, density, and heat capacity. After extensive evaluation and hyperparameter tuning, linear regression demonstrated the best performance, achieving a high coefficient of determination (R2 = 0.9851) on the test data. This robust predictive model offers a reliable tool for assessing the behaviour of hydrogen mixtures under subsurface conditions The findings provide critical insights into the thermophysical properties and phase behaviour of hydrogen mixtures, aiding in the selection of optimal gas compositions for UHS. By leveraging data-driven approaches alongside thermodynamic modelling, this study lays the foundation for scalable and efficient UHS systems in Nigeria and beyond.