WP 1.7
An improper operation of gas storage in the deeper underground may potentially lead to a leakage of gases into near-surface aquifers. The possible or likely effects of a gas intrusion depend on the type of the gas as well as of the geochemical environment of the aquifer. So, the entry of compressed air may cause oxidation reactions, while the entry of methane or hydrogen may cause microbial catalyzed reduction reactions. In addition to the direct impact on the ground water quality due to the solution of gases, the impact of the possible subsequent redox reactions on the composition of the water are to be investigated. The initiated redox reactions are of interest also in connection with the installation of a monitoring network and the definition of monitoring targets, because a complete geochemical utilization of the dissolved gases is possible.
The laboratory experiments developed and conducted in this work package investigate the effects of leakages of H2, CH4 or compressed air in near surface aquifers. The aims of the experiments are an improvement of process knowledge, the identification of appropriate parameters for the implementation of the initiated redox reactions in transport-reaction-models, and the identification of monitoring parameters. In addition, a central question is whether results from experiments performed under normal pressure conditions are transferable to in-situ conditions allowing the development of suitable transfer function. For this approach, experiments will be carried out at gas pressures of up to 30 bars. The results will be evaluated concerning a dependency between gas pressure and reaction kinetics as well as equilibrium reactions. The practical question on these experiments is, whether a risk assessment for a real gas storage project strongly requires experiments at in-situ conditions or whether results of experiments conducted at normal conditions can be scaled up simply by assuming higher pressure conditions and using a validated transfer function. The latter would be a cost saving approach. Furthermore, the evaluation of the results by using simple geochemical models provides an abstraction and generalization of the observed geochemical processes resulting in a reaction scheme which can be included in more complex simulation performed in other work packages (WP 3.3 and WP 3.4).
