## 3 Results and Discussion
### Influencing Factors
#### 3.4.3 Kinetic Rate Constant  
Special consideration is given to the influence of the kinetic rate constants of bacterial sulfate reduction and methanogenesis on the loss of hydrogen during storage. Therefore, the rate constants are varied. As a reminder, the initial kinetic rate constant in the reference scenario for BSR is 9.26 \(\times\) 10\({}^{-8}\) mol kgw\({}^{-1}\) s\({}^{-1}\) and 2.30 \(\times\) 10\({}^{-9}\) mol kgw\({}^{-1}\) s\({}^{-1}\) for methanogenesis.  
By increasing the kinetic rate constant for BSR slightly to 2.40 \(\times\) 10\({}^{-7}\) mol kgw\({}^{-1}\) s\({}^{-1}\), based on data from [PERSON] et al. [52], the total amount of stored hydrogen is lost in less than 20 years. The amount of generated H\({}_{\text{2}}\)S\({}_{\text{(g)}}\) does not change because the reactive amount of anhydrite in the reservoir rock is completely consumed and the only sulfate source comes from the cap rock and underlying rock by diffusion and diffusion is a slow process. By increasing the storage time to 300 years (with a kinetic rate constant of 2.40 \(\times\) 10\({}^{-7}\) mol kgw\({}^{-1}\) s\({}^{-1}\) for BSR), the effect of diffusion is recognizable and the H\({}_{\text{2}}\)S\({}_{\text{(g)}}\) generation increases in the hotspot areas. The amount of generated CH\({}_{\text{4(g)}}\) increases from 0.2 mol L\({}^{-1}\) of gas to an average of 0.25 mol L\({}^{-1}\) of gas in each cell of the reservoir rock after 30 years (Figure 2d). The reason for this could be that methanogenesis starts as soon as all the sulfate for BSR is consumed. Because sulfate is consumed faster, due to the increased kinetic rate constant, the timeframe in which the methanogenesis can take place is expanded. On decreasing the kinetic rate constant for BSR to 9.26 \(\times\) 10\({}^{-9}\) mol kgw\({}^{-1}\) s\({}^{-1}\), the amount of generated H\({}_{2}\)S\({}_{(\mathrm{g})}\) does not change because the reactive amount of anhydrite in the reservoir rock is completely consumed. Less H\({}_{2(\mathrm{g}/\mathrm{aq})}\) is consumed (14% loss) and a smaller amount of CH\({}_{4(\mathrm{g})}\) (on average 0.013 mol L\({}^{-1}\) of gas) is generated (Figure 2e).  
At a higher kinetic rate constant for methanogenesis of 2.30 \(\times\) 10\({}^{-6}\) mol kgw\({}^{-1}\) s\({}^{-1}\), the total amount of stored hydrogen is lost in less than 6 years (Figure 2f). CH\({}_{4(\mathrm{g})}\) production increases to an average of 0.25 mol L\({}^{-1}\) of gas and the mass of water rises to 1.03 kg per cell in the reservoir rock after 30 years of storage. The amount of CO\({}_{2(\mathrm{g})}\) from the injected gas mixture and the residual gas is completely consumed in less than 3 years of storage and is not the limiting factor for methanogenesis. If no CO\({}_{2(\mathrm{g})}\) is available anymore from the injected gas mixture and residual gas, the dissolution of carbonate-bearing minerals begins and delivers CO\({}_{2}\) for methanogenesis. With a smaller kinetic rate constant for methanogenesis of 2.30 \(\times\) 10\({}^{-12}\) mol kgw\({}^{-1}\) s\({}^{-1}\), the loss of H\({}_{2(\mathrm{g}/\mathrm{aq})}\) is slightly lower (75.7%). Less CH\({}_{4(\mathrm{g})}\) is generated (but the differences are in the third decimal place, only from 0.192 mol L\({}^{-1}\) of gas in the reference scenario to 0.191 mol L\({}^{-1}\) of gas) and the H\({}_{2}\)S\({}_{(\mathrm{g})}\) generation is constant (Figure 2g). The produced mass of water and the pH conditions show no changes compared to the reference scenario.  
It can be concluded that the kinetic rate constants are important factors controlling the loss of hydrogen storage. Knowledge of the kinetic rate constants for BSR and methanogenesis at elevated temperature and pressure are required. Nevertheless, the maximal amount of generated H\({}_{2}\)S\({}_{(\mathrm{g})}\) is, if all reactive sulfate-bearing minerals (e.g., anhydrite) are consumed, limited by diffusion. On the other hand, the maximal amount of generated CH\({}_{4(\mathrm{g})}\) depends on the kinetic rate constant and the storage time.