Underground methane storage is known as a promising option to synchronize sustainable energy production with variable consumption demand. This work aims to develop a model for underground biological methanation considering the presence of microorganisms. Model is described by a compositional two-phase flow in a porous medium saturated by water and gas and the existence of chemical species as components (H2, CO2, CH4, and H2O). H2 and CO2 are injected into a depleted gas reservoir and slightly dissolve into the water phase. Microorganisms feed on H2 and CO2 as the energy source and produce CH4. This model is numerically simulated for a four-year production and injection to optimize methane production.
For this purpose, first, the different solvers of MRST were validated by Eclipse commercial software, and then a base case was defined and ran according to the data gathered from the literature. Finally, the effects of thermodynamic and bacterial parameters such as initial reservoir temperature and pressure, growth and decay rate of bacteria, and the number of microorganisms were investigated on methane production rate.
The results showed that the injection of gas with 80% hydrogen content caused a sharp front in the reservoir which moves towards production well over time. The notable difference in the initial composition of the reservoir gas and the injection gas caused this front. But In the case of bacterial activity, it was observed that due to their feeding from the injected gas and methane production, this front was not very sharp and the pressure distribution in the reservoir was more uniform.
Also, the sensitivity analysis demonstrated that methane production increased with a rise in the reservoir initial pressure and the number of microorganisms while the increase in temperature and bacterial degradation rate led to a reverse effect. Also, according to the selected base value for the microorganisms’ number, the effect of growth rate changes on the output was no
