To meet the demand of peak loads, renewable energy can be converted into hydrogen, which can be mixed into natural gas and stored in subsurface structures. Therefore an assessment of the influence of hydrogen methane mixtures on potential storage formations is needed. This thesis attempts to give an overview of what is already known about hydrogen-rock interaction and were more work needs to be done. Additionally, a fluid-gas-rock interaction model has been generated to make a first quantitative assessment of what influences hydrogen methane mixtures have on the geochemistry of potential subsurface storage structures To get comparable results for a field test, which might be conducted after this thesis, a thermodynamic model was generated. The mineralogy and chemistry is taken from two representative core samples: one of them from the same formation as expected by the anticipated field test, and one with a similar mineral composition. A problem of generating the model was to get reliable thermodynamic data for clay minerals. Thermodynamic data for clay minerals is very difficult to generate, because of their numerous components and compositions which make an assessment challenging. Therefore, not all clay minerals which are present in the rock samples could be included into the model. Fluid-gas-rock interaction models have been run for different gas compositions (0-100% hydrogen in the methane) and different pressure and temperature conditions The model shows that the titration of hydrogen changes the pH and Eh of the tested fluid. A pH is increase leads to dissolution of dolomite and precipitation of calcite. Additionally the generation of talc is observed. A potentially major issue is the stability of sulphides in the reservoir i. e. the generation of H2S which would be harmful to health and environment. The models indicated however that the H2 does not destabilize the sulphides. The influence of temperature and pressure on the mineral assembly in the storage reservoirs has also been assessed. Within the range of plausible variations the influence of temperature is only minor and that as long as the phase is supercritical pressure does not influence the conditions at all.