The global energy market is currently facing a period of transition. To fight the ongoing global warming and to push the decarbonization towards the end of the current century, several countries all over the globe have decided to move from fossil fuels to renewable energy sources in the sector of power generation. The inconstant baseload of those renewable energy sources, such as wind and solar power, created a certain necessity for large-scale energy storage. The idea is to store the power if a surplus is available, and to provide to the grid in case of a lack of energy. Hydrogen gas is an acutely flexible and effective energy carrier, which can be generated via renewable energy in times of surplus. Due to the limited capacity of conventional hydrogen storage techniques, like batteries, depleted gas reservoirs serving as underground hydrogen storage (UHS) are gaining more and more attraction to store large quantities of energy. This work is based on a doctoral thesis, which was related to UHS in porous media, where a series of experiments were carried out. Among those was an ink-injection experiment, which fueled the suspicion of the presence of a micro-porosity in the accumulated biomass. The experimental results are an integral part of this master thesis. In this work, the presence of an internal permeability and porosity of accumulated biomass in porous media is studied. Therefore, a numerical model was set up to conduct flow simulations with experimental segmented images with different scenarios and both, uniform and varying permeability as well as porosity cases. Furthermore, the flow field was analyzed in detail. This is the second major topic in this master thesis and is related to the mass transport and nutrient supply within the accumulated biomass. Hence, a python script was written to extract the velocity values between two points of interest within the calculated volume field. To examine whether the supply of nutrients is a result of pure diffusion or rather advection-dominated, the dimensionless Péclet number was calculated in different clusters scattered across the total domain. This master thesis attempts to contribute to a broader understanding which is relevant for hydrogen storage and conversion operations. The major objective of this research was to survey new concepts via numerical modeling that are significant in the sector of underground energy conversion and storage.