Hydrogen storage in geological systems – potential for biological methanation

In the frame of the SAMUH2 project water samples were taken at a geological pore gas storage. In the course of the abandonment of a natural gas storage, deep fluids could be recovered from a depth of 500 - 600 meters. A total of eight boreholes were sampled from injection and observation wells. The focus of the investigations was on the analysis of the chemical composition of the fluids as well as the characterization of the microbial biocoenosis and partly also their metabolic activity.

Organic acids were detected in varying concentrations and compositions in both the fluid samples taken at the injection and observation wells. Organic acid concentrations ranged from 0.1 to 730 mg/L. Gen copies of Bacteria, sulfate reducers (SRB) and methanogenic archaea were detected in all fluids by qPCR. A detailed characterization of the microbial community was carried out by microbiome analysis. A diverse microbial community was detected on fermenters and methanogenic archea. Sulfate reducers, on the other hand, were identified predominantly in the observation wells.

Several laboratory experiments demonstrated that the fluids of injection wells contained an active biocenosis capable of hydrogenotrophic methanogenesis. In contrast, only one observation well fluid demonstrated the activity of hydrogenotrophic methanogenic archaea. The capability of underground storage facilities for producing eco- ("green") methane is a further topic of this study.