Seasonal Hydrogen Storage in Dutch Depleted Gas Reservoirs

Abstract

The Netherlands will need to transform her traditionally fossil fueled energy system in the coming decades to achieve the goal of reducing CO2 emissions to net-zero in 2050. Therefore, an increase in renewable energy sources as solar and wind energy in the overall energy mix will be essential. However, due to the highly variable energy production patterns of these renewable energy sources, a primary need for energy storage is created. Since electricity can not be stored on a large enough scale to balance significant energy fluctuations, the need for a gaseous CO2 neutral energy carrier is created. In The Netherlands, this role could potentially be fulfilled by green hydrogen gas. Green hydrogen can be stored in geological formations such as depleted gas reservoirs. Due to the immense storage volumes and frequent occurrence in the Dutch subsurface, depleted gas reservoirs could be an excellent opportunity to serve as large scale energy storage sites. Moreover, underground natural gas storage in gas reservoirs is a proven and used technique in The Netherlands. Utilizing a natural gas reservoir as a hydrogen storage site comes with several challenges. This report provides a full overview of all the challenges with underground hydrogen storage in geological formations as aquifers, depleted gas reservoirs and salt caverns based on literature. In this way, the full potential and risks of using depleted gas reservoirs for this technique is clearly highlighted. Using this overview, a priority scheme for the usage of different geological formations as storage facilities for hydrogen is proposed. In combination with possible meteorological conditions combined with different Dutch policy scenarios, a minimum seasonal storage need of 16 TWh through the use of hydrogen is identified. Using the priority scheme, rock salt caverns are used as much as possible to fulfill the minimal need for seasonal hydrogen storage. By performing an analysis on the potential subsurface storage capacity in The Netherlands, it becomes clear that the Dutch subsurface can not realize more than 12.1 TWh of potential hydrogen storage capacity by only utilizing salt caverns. Since depleted gas reservoirs are identified as the best alternative for underground hydrogen storage, a minimum need for hydrogen storage from Dutch depleted gas reservoirs is estimated at 3.9 TWh in 2050. In this thesis, all physical and chemical aspects that are important during the subsurface storage of hydrogen in porous media are addressed. This leads to the identification of potential losses of hydrogen during the storage of the gas in the depleted gas reservoir. Analyzing all the possible methods leading to potential hydrogen loss shows that on the long term, bacterial conversion seems to be the biggest challenge if no measures against this conversion are taken. Using numerical reservoir simulation as a quantification and sensitivity analysis tool, the hydrodynamic behaviour of hydrogen in contact with other gasses is described. This is done by introducing a dimensionless gravity number. The interpretation of this number shows if the displacement process is either dominated by viscous or gravitational forces. Furthermore, the displacement efficiency of hydrogen towards other gasses is analyzed. Displacement of hydrogen towards residual gasses in porous media dominated by viscous forces proves to be more efficient than the displacement dominated by gravitational forces. By performing cyclic storage simulations, the overall efficiency of injecting and reproducing hydrogen from a depleted gas reservoir is examined. This is done for both homogeneous and heterogeneous reservoirs. By performing a sensitivity analysis on the input parameters of the simulator, an overview is given of the parameters that will have the most positive or negative impact on the cycle efficiency. The results of the simulation show a regular cycle efficiency that is estimated at roughly 70%. Applying a higher difference in injection and production pressure leads to a lower cycle efficiency whereas using a more elongate reservoir as storage site shows to have a positive effect on the overall cyclic efficiency.