Caprock -Reservoir Integrity of Subsurface Storage of Hydrogen (CRISTHY)

Underground hydrogen storage (UHS) has been promoted as one of the feasible solutions to support the global hydrogen economy. In addition to the operational challenges in hydrogen storage, addressing the fundamental physical-chemical processes involved in UHS is crucial. Although there are similarities between UHS and natural gas, compressed air, and CO2 subsurface storage, there are unique differences due to the physical and chemical properties of hydrogen. To ensure the safe and efficient storage of hydrogen, the following processes need to be investigated Hydrogen does not dissolve in water, making the buoyancy effects much stronger than CO2 and natural gas.The significant difference in density between hydrogen and brine causes hydrogen to migrate upwards quickly and separate into different phases. However, hydrogen can also spread laterally over a wider area due to its low viscosity. As the flow moves away from where it was injected, the fluid velocity decreases, causing the front of the flow to becomedominated by capillary forces. During the hydrogen production stage, capillary trapping may occur, which can cause the brine to leave behind hydrogen due to the start of the imbibition process.Likewise, the presence of reservoir heterogeneity (Non uniform distribution of rock properties) makes dynamic properties like relative permeability and capillary pressure very important.In order to minimise the hydrogen loss due to the different flow complexity mentioned above, we will utilise two-phase flow simulation methods. This will include the implementation of simplified models to understand the long-term impact of UHS on reservoir caprock integrity. In addition, the complicated two-phase flow simulation method will be used to study the effect of reservoir heterogeneity and fluid properties on hydrogen injectivity and productivity. Numerical models will also be used to verify the validity of the measured hydrogen flow properties, such as relative permeability.
The project's First yearis mainly focused on the flow and transport of hydrogen in aquifers.As hydrogen is much lighter than brine, strong buoyancy forces pushhydrogen to the caprock. This would lead to fast segregation of hydrogen and brine and hydrostatic pressure profile in the vertical direction. Using this assumption, we have utilised a simplified reservoir simulation method that reduces the number of dimensionsby one. Therefore, we can investigate the long-term effect of UHS and other activities, such as microbial and geochemical.Relative permeability is a contributing factor in hydrogen flow, so its accurate measurement is necessary. In addition to relative permeability, gas viscosityis a defining parameter in hydrogen mobilityin the presence of brine. As hydrogen mobility is much higher than water, there is ahigh probability ofviscous fingering effect at labscale measurements.We have conducted lab-scaled simulations to see whether the reported relative permeability in the literature is reliable on the field scale. Hydrogen may be responsible for the growth of hydrogen consuming microbes in the subsurface.Microbial activity inside depleted or brine reservoirs can pose a threat to hydrogen security and also reservoir-caprock integrity. There are a variety of microorganisms that consume hydrogen, including methanogens, sulfate reducers, homoacetogenic bacteria, and iron (III)reducers. The injection pressure-temperature condition, pH value of brine, and substrate supply are essential factors affecting hydrogen consumption. In addition to hydrogen loss due to microbial activity, microorganisms can also plug the pores of the reservoir, leading to a decrease in reservoir injectivity/productivity. In order to gain a comprehensive understanding of how microbes consume hydrogen at a reservoir level, it is necessary to integrate flow models with microbial reaction models and conduct experimental tests or employ porescale modelling