EAGE/DGMK Joint Workshop on Underground Storage of Hydrogen

The overall objective of the research project H2STORE was to build practical experience on a laboratory scale on biochemical and geochemical processes with different hydrogen/natural gas mixtures. All tests were run on different reservoir rocks of various, German reservoirs. The research project HyINTEGER focused more on the interaction of the different reservoir rocks with the wellbore cement and the casing.

Underground hydrogen storage (UHS) coupled to the power-to-gas technology as potential energy storage for renewable energies gained more attention within the last years. In order to plan and calculate the technical and economic feasibility of an UHS, the processes occurring in the subsurface have to be understood. This study presents a successful history match of a hydrogen storage field test, where microbial activity was identified during hydrogen injection. Therefore, the field data was implemented into a dynamic model in the open-source software DuMux. With the used mathematical model, which describes the bio-reactive flow in the reservoir, the change of gas compositions in the withdrawn gas was matched. For the matching process, the initial microbial density and the diffusion coefficients of CO2 and H2 into CH4, were adjusted.

Based on extensive experiences from previous case studies, laboratory analyses on several gas caverns and porous underground gas storages as well as many years of research it is known that most potential H2-underground storages are already colonized with microorganisms which can consume hydrogen as sole energy source. Particularly relevant to a feed-in of hydrogen are methanogenic Archaea and especially sulfate-reducing Prokaryotes (SRP). In addition to chemical changes in the formation water and blockage of the pore space, SRP leads in particular to a formation of hydrogen sulphide (H2S). Because of the dominance and resilience of SRP to adverse living conditions (tolerance to high pH, temperature, mineralization), we find this group of microorganisms in numerous gas storages as well as in oil and gas reservoirs. In contrast to caverns, pore reservoirs offer favorable conditions for microbial growth due, among other things, to large growth surfaces, pressure-driven flow processes, complex minerals (carbonate, sulfate, etc.) and often low mineralization. Our many years of experience suggest that feeding hydrogen into microbially colonized underground pore reservoirs will inevitably lead to stimulation of the microbial population. Hence, the foreseeable microbial risks of hydrogen injection into porous underground storages must therefore be discussed.

The storage of hydrogen in porous underground gas storages is a promising solution for large-scale energy storage in Germany. This solution provides a cost effective and large capacities in comparison to other storage types, however hydrogen interactions in UGS is a perplexing topic due to its foreign nature and therefore its behavior in the subsurface could be unpredictable. The HyInteger Project was tasked with investigating the integrity of subsurface equipment and near wellbore region in strongly corrosive environments in porous UGS containing hydrogen for long-term safe and reliable storage. Hydrogen interactions with the near-wellbore region in underground gas storages are investigated in small-scale laboratory experiments. Autoclaves are implemented to recreate typical underground gas storage conditions containing hydrogen gas. Pressures up to 200 Bar and temperatures up to 120°C can be achieved allowing for a huge range of testing possibilities and research avenues to be explored. Petro-physical, geochemical and material investigations are carried out in order to observe potential changes to the near-wellbore region and its subsurface equipment due to hydrogen presence.

There is little knowledge on the relevant physico-chemical parameters that govern the interaction between hydrogen and reservoir fluids under typical reservoir conditions, which are high salinity, elevated temperature and pressure. Furthermore, high gas losses through diffusion are assumed. As a first step, hydrogen solubilities in synthetic reservoir brines with chloride as anion and Na, Mg, K as cations were determined. Concentrations from 0 to ≤5 molar were individually investigated for a grid of temperatures ranging from 25 to 100 °C and pressures ranging from 1 to 250 bar. The experiments span a three dimensional space with the base factors of concentration, pressure and temperature. In pure water at 25°C, results are in good agreement with predicted values from standard model (PHREEQC, EOS of Spycher & Reed, 1988). However, the solubilities for higher salinity with variable pressure and temperature are more than four times higher compared to predictions from the current standard model. Besides the solubility measurements, experiments to determine diffusion coefficients of the rock types sandstone, claystone and salt rock are planned. For this purpose a novel designed apparatus is under construction and close to finalization. Experiments will follow the construction.