Underground Hydrogen storage (UHS) is an attractive technology for large-scale energy storage. The UHS safety and efficiency depends highly on accurate characterization of H2 interactions with reservoir fluids, specially wettability analyses for H2/brine/rock systems. This thesis reports experimental measurements of advancing and receding contact angles of H2/water, N2/water and CO2/water systems at P = 10 bar and T = 20 °C using a microfluidic chip (channel widths: 50 - 130 μm). The results indicate strong water-wet conditions with H2/water advancing and receding contact angles of respectively 13 - 39°, and 6 - 23°. It was found that the contact angles decrease with increasing channel widths. Little hysteresis was measured, and consequently, the results are not in line with Morrow’s curve. The receding contact angle measured in the smallest channel agrees well with the literature coreflood tests. The N2/water and CO2/water systems showed similar behaviours as the H2/water system.

This study investigates the thermal recharge of deep geothermal reservoirs by free convection. A coupled numerical model that is built in Comsol Multiphysics is presented in order to estimate the thermal recharge during the first 30 years of production from a typical high enthalpy geothermal reservoir. A sensitivity analysis was carried out to find which parameters have most significant impact on the thermal recharge by free convection and reservoir lifetime. The sensitivity analysis is mainly focussed on fault properties. The developed model consists of a reservoir with two confining layers and vertical faults. This model is used to calculate the produced energy, extracted energy from the reservoir and the recharge by conduction based on which the thermal recharge by free convection can be calculated. Results show that free convection is a significant part of the produced energy. Therefore, it is important to take free convection into account by estimating the recoverable energy. From the results can also be concluded that fault aperture, fault height, fault permeability and thermal conductivity of the confining layers have a significant impact on the thermal recharge by free convection of a faulted geothermal system. Fault density also has impact on the thermal recharge, but the relation between fault density and thermal recharge by free convection is less clear. Thermal conductivity of the reservoir rock has no impact on the thermal recharge by free convection according to the results of this model.