Application of surface gas geochemistry in monitoring of underground hydrogen storage

Results: of geochemical modeling of potential gas seepage (microseepage) from a demand gas storage reservoir that is being converted from methane to hydrogen storage are presented. Buoyant gas transport through the saturated zone in response to pressure is the hypothesized mechanism that is explored with computer modeling. The unsaturated or vadose zone is modeled using a diffusion model that is coupled with microbial oxidation or methanotrophy in the vadose zone. Computed methanotrophic oxidation during vertical migration with isotopic fractionation is used to understand processes operating. An analogous hydrogenotrophic process is hypothesized to occur which is evaluated by the same methodology. Application of the model to interpret data collected earlier at two locations is described. These measurements primarily using methane, in addition to the saturated zone model is used to develop a proposed protocol for a baseline study, planning, implementation, and monitoring program of a hydrogen demand gas storage reservoir. The proposed protocol can provide geochemical data to evaluate the economic and environmental effectiveness of a project.