PVT Analysis for Hydrogen and Methane Mixtures for Underground Hydrogen Storage

Hydrogen has been identified as an energy carrier that could play a major role in decarbonization. Large-scale hydrogen storage is required to face future challenges in terms of energy and environmental transition. Underground Hydrogen Storage (UHS) in depleted gas reservoirs is broadly recognized as a promising strategy to safely store large quantities of hydrogen, which can be injected into the porous rocks as a pure component (100% of H2) or as a mixture with methane. In order to properly design storage activity in a depleted gas reservoir, it is extremely important to define a reliable 3D reservoir dynamic model able to simulate the behavior of the system under all the possible considered operating conditions. To properly represent the interaction between injected hydrogen or mixture with the reservoir fluids, the Equations of state adopted in the compositional simulation must be validated against laboratory data in the pressure and temperature ranges representative of possible operating conditions, and if necessary, properly calibrated. In this paper, we provide the results of experiments carried out on H2-CH4 mixtures within ranges of temperature and pressure conditions representative of depleted gas candidates for storage activities. Constant Mass Expansion (CME) tests were performed using a PVT cell. Pressures up to 300 bar and a temperature range from 30 to 60°C, representing the typical range for a gas storage reservoir in Italy and Europe, were applied. Four different mixtures were considered: pure H2, 50 mole% H2-50 mole% CH4, 10%H2-90 mole% CH4, pure CH4. Results are represented in terms of gas compressibility factor (z factor) curves as a function of pressure for different temperatures and compositions. Furthermore, the obtained results are compared with the GERG-2008 equation of state (EoS). In the considered pressure and temperature ranges, the GERG-2008 EoS provides a satisfactory match with the experimental data for all the considered cases.