Laboratory Experiments for Safe Underground Hydrogen/Energy Storage in Depleted Natural Gas Reservoirs

Fluctuating energy production by renewable sources increases the demand for energy storage capacities, especially caused by the ongoing installation of wind power plants and photovoltaic sites. Transforming electricity into hydrogen, which is used as an energy buffer, will help stabilize electrical grids and provide a safe and reliable energy supply. In this context the storage of large volumes of H2 and H2-bearing gas mixtures in sealed depleted gas fields is a possible option. Borehole casings, tubing and cements may, however, be affected by high temperature, pressure and formation fluid salinity in these heterogeneous sedimentary rocks in the presence of H2 and negatively affect secure hydrogen storage. Preliminary results from laboratory experiments with hydrogen under reservoir conditions indicate that high reservoir temperature (>100°C), pressure (>15 MPa) and formation fluid salinity (TDS >200 g/l) may indeed promote the surface alteration of borehole steel alloys and induce the dissolution of pore-filling mineral (anhydrite, barite, some carbonate species) in the reservoir due to physico-chemical variations in the formation fluids. No such reactions were observed at lower values, suggesting that safe hydrogen storage may be possible under less harsh conditions.