The potential applications of hydrogen as an energy vector as a part of the solution to decarbonize emissions from use of natural gas and transportation is the subject of much research. Hydrogen storage in the geological subsurface helps to mitigate the effects of fluctuating energy production from renewable energy sources. Nevertheless, there is little comprehensive work on full scale simulation of all the processes associated with the injection, storage and re-producing of hydrogen.
Physical phenomena involved in this process include mixing of hydrogen with native components in the reservoir and potentially cushion gas, ga, relative permeability hysteresis, solubility of various gases into the aqueous phase; effect of hydrogen impurity (e.g., CO2, H2S, CH4) and bio-methanation in the presence bacteria. Numerical simulation can be used for dynamic numerical modelling of the storage when all these complex processes are in action.
Solubility of hydrogen can be modelled using a solubility table, Henry's correlation, or K-values table. The effect of other gases on the geochemistry of the rock and fluid can be studied in detail using chemical and geochemical reaction concepts. The activity of bacteria in an underground hydrogen storage field may result in synthetic methane production. Such reactions can be modelled based on bacterial activity levels using Arrhenius type reactions. The level of biomass activity depends on salinity, temperature and bacterial types and availability of nutrients.
A sub-sector from a North Sea reservoir is used to simulate these processes described and predictions of individual injection/production at various cycles are created. Issues regarding improved monitoring and design of laboratory experiments for future field operations are highlighted. This study shows how simulation can be instrumental in understanding and designing underground hydrogen storage projects, providing predictions of storage volumes, produced gas quality and quantity under various scenarios. The paper also describes the reaction parameters, upscaling, and tuning techniques required for simulation at full field scale.