ALBERT

Description: The large scale storage of energy is a great challenge arising from the planned transition from nuclear and CO2-emitting power generation to renewable energy production, by e.g. wind, solar, and biomass in Germany. The most promising option for storing large volumes of excess energy produced by such renewable sources is the usage of underground porous rock formations as energy reservoirs. Some new technologies are able to convert large amounts of electrical energy into a chemical form, for example into hydrogen by means of water electrolysis. Porous formations can potentially provide very high hydrogen storage capacities. Several methods have to be studied including high hydrogen diffusivity, the potential reactions of injected hydrogen, formation fluids, rock composition, and the storage complex. Therefore, in August 2012 the collaborative project H2STORE ("hydrogen to store") started to investigate the feasibility of using burial clastic sediments of depleted gas reservoirs as well as recently used gas storage sites as potential hydrogen storage media. In Germany, such geological structures occur at various geographic sites and different geological strata. These deposits are characterized by different geological-tectonic evolution and mineralogical composition, mainly depending on palaeogeographic position and diagenetic burial evolution. Resulting specific sedimentary structures and mineral parageneses will strongly control formation fluid pathways and associated fluid-rock/mineral reactions. Accordingly, H2STORE will analyze sedimentological, petrophysical, mineralogical/geochemical, hydrochemical, and microbiological features of the different geological strata and the German locations to evaluate potential fluid-rock reactions induced by hydrogen injection. Such potential reactions will be experimentally induced in laboratory runs, as analogues for naturally occurring processes in deep seated reservoirs. Finally, rock data determined before and after these experiments will be used as major input parameters for numerical modelling of mineralogical and microbiological reactions. Such reactions are expected to have a strong affect on rock porosity-permeability evolution and therefore the characteristics of flow processes in reservoir and the barrier properties of sealing rocks. The special topic of this study will be the modelling of hydrogen propagation in the subsurface reservoir formation supplemented by its mixing with the residual gases as well as the simulation of coupled bio-dynamic processes and of reactive transport in porous media. These numerical simulations will enable the transfer of experimental results from the laboratory runs to the field-scale and the formulation of the requirements for hydrogen storage in converted gas fields. Thus, the major objectives of H2STORE are to obtain fundamental data on the behaviour of clastic sediments in the presence of formation fluids and injected hydrogen, its impact on petrophysical features and the development of the most realistic modelling for proposed and experimentally induced rock alteration as well as complex gas mixing processes in potential geological hydrogen reservoirs. Moreover these results will be used when discussing the possibility of "green" eco-methane generation by hydrogen and carbon dioxide interaction in the geological underground.

Description: The large scale storage of energy is a great challenge arising from the planned transition from nuclear and CO2-emitting power generation to renewable energy production, by e.g. wind, solar, and biomass in Germany. The most promising option for storing large volumes of excess energy produced by such renewable sources is the usage of underground porous rock formations as energy reservoirs. Some new technologies are able to convert large amounts of electrical energy into a chemical form, for example into hydrogen by means of water electrolysis. Porous formations can potentially provide very high hydrogen storage capacities. Several methods have to be studied including high hydrogen diffusivity, the potential reactions of injected hydrogen, formation fluids, rock composition, and the storage complex. Therefore, in August 2012 the collaborative project H2STORE ("hydrogen to store") started to investigate the feasibility of using burial clastic sediments of depleted gas reservoirs as well as recently used gas storage sites as potential hydrogen storage media. In Germany, such geological structures occur at various geographic sites and different geological strata. These deposits are characterized by different geological-tectonic evolution and mineralogical composition, mainly depending on palaeogeographic position and diagenetic burial evolution. Resulting specific sedimentary structures and mineral parageneses will strongly control formation fluid pathways and associated fluid-rock/mineral reactions. Accordingly, H2STORE will analyze sedimentological, petrophysical, mineralogical/geochemical, hydrochemical, and microbiological features of the different geological strata and the German locations to evaluate potential fluid-rock reactions induced by hydrogen injection. Such potential reactions will be experimentally induced in laboratory runs, as analogues for naturally occurring processes in deep seated reservoirs. Finally, rock data determined before and after these experiments will be used as major input parameters for numerical modelling of mineralogical and microbiological reactions. Such reactions are expected to have a strong affect on rock porosity-permeability evolution and therefore the characteristics of flow processes in reservoir and the barrier properties of sealing rocks. The special topic of this study will be the modelling of hydrogen propagation in the subsurface reservoir formation supplemented by its mixing with the residual gases as well as the simulation of coupled bio-dynamic processes and of reactive transport in porous media. These numerical simulations will enable the transfer of experimental results from the laboratory runs to the field-scale and the formulation of the requirements for hydrogen storage in converted gas fields. Thus, the major objectives of H2STORE are to obtain fundamental data on the behaviour of clastic sediments in the presence of formation fluids and injected hydrogen, its impact on petrophysical features and the development of the most realistic modelling for proposed and experimentally induced rock alteration as well as complex gas mixing processes in potential geological hydrogen reservoirs. Moreover these results will be used when discussing the possibility of "green" eco-methane generation by hydrogen and carbon dioxide interaction in the geological underground.

Description: Modelling fluid–rock interactions induced by CO2 is a key issue when evaluating the technical feasibility and long-term safety assessment of CO2 storage projects in deep formations. The German R&D programme CLEAN (CO2 Large-Scale Enhanced Gas Recovery in the Altmark Natural Gas Field) investigated the almost depleted onshore gas reservoir located in the Rotliegend sandstone at over 3,000-m depth. The high salinity of the formation fluids and the elevated temperature in the reservoir exceed the validity limits of commonly available thermodynamic databases needed for predictive geochemical modelling. In particular, it is shown that the activity model of Pitzer has to be applied, even if necessary input data for this model are incomplete or inconsistent for complex systems and for the considered temperatures. Simulations based on Debye- Hu¨ckel activity model lead to severe, systematic discrepancies already in the simple proposed reference case where experimental data could be used for comparison. A simplified geochemical model, consistent with the average measured composition of formation fluids and the prevailing mineralogical assemblage of the host rock, identifies the mineral phases most likely to be considered at equilibrium with the formation fluid. The simulated reactions due to CO2 injection, under the hypothesis of local thermodynamical equilibrium, result in a moderate reactivity of the system, with the dissolution of anhydrite cementation and haematite being the most relevant expected mineral reactions. This is compensated, at equilibrium, by the precipitation of new carbonates, like calcite and siderite, for an overall very small loss of porous space. The simulated rather small effect of mineral alteration is also due to the scarce amount of water available for reactions in the reservoir. The results of the model are qualitatively in line with observations from batch experiments and from natural analogues.