Auswirkungen von H2 und CO2 Untergrundspeicherungen auf die Reservoireigenschaften von Sandsteinen : mineralogische Untersuchungen und hochauflösende Computertomographie Modellierungen aus HPHT Autoklaven Laborexperimenten This study was conducted as part of the research project Hydrogen to Store (H2STORE) with the focus of potential reactions of reservoir sandstones and formation fluids exposed to injected hydrogen and carbon dioxide. Therefore sandstone samples of three Rotliegend drilling wells and one Buntsandstein bore hole were investigated because these stratigraphic units form the most important underground storage sites in Germany. The material was provided by industrial partners. The characterization of lithological petrographical and geochemical features as well as the microscopical documentation (by Field Emission Scanning Electron Microcopy FE SEM Digital Microscope System DMS Atomic Force Microscopy AFM) of mineral surfaces measurements of specific surface areas and of petrophysical properties (porosity permeability) and high resolution computed tomography (μ CT) associated with numerical simulations were conducted before and after static autoclave experiments to evaluate potential reactions induced by these tests. The experiments are performed under specific reservoir conditions (reservoir pressure reservoir temperature formation fluid composition) combined with H2 or CO2 exposure and running times of four to seven weeks. After the autoclave experiments the dissolution of pore filling carbonate anhydrite and barite (only after H2 experiments) is established as shown by geochemical and hydrochemical data µ CT scans and microscopic sample surface studies by FE SEM AFM and DMS. The variation of mineral surfaces and the dissolution of pore filling cements increased the size of specific surfaces areas and modified the petrophysical properties of the sandstones. These results in a variation of the size and direction of fluid pathways and in pore size distribution are also simulated by μ CT data. The modelled results of these analyses are in good agreement with the measured results achieved by conventional experimental methods (He porosity N2 permeability).