A coupled, pore-scale model for methanogenic microbial activity in underground hydrogen storage

• Development of a model for the microbial conversion of hydrogen in UHS.
• Gas flow is simulated on the pore scale using Stokes’ equations.
• Multispecies microbial activity within biofilms is accounted for with a separate model.
• The two models are coupled via boundary conditions.
• A sample simulation shows the biofilm growth process within films of residual water.

Underground hydrogen storage (UHS) as a means of energy storage is an efficient way of compensating for seasonal fluctuations in the availability of energy. One important factor which influences this technology is the activity of methanogenic microorganisms capable of utilising hydrogen and carbon dioxide for metabolism and leading to a change in the stored gas composition. A coupled, pore-scale model is presented which aids in the investigation of the mechanisms that govern the conversion of hydrogen to methane, i.e. advective hydrogen flow, its diffusion into microbial biofilms of multiple species, and its consumption within these biofilms. The model assumes that spherical grains are coated by a film of residual water and treats the biofilm development within each film in a quasi one-dimensional manner. A sample simulation using the presented model illustrates the biofilm growth process in these films as well as the competition between three different microbial species: methanogens, acetogens, and acetotrophs.