Overcoming the intermittency problem of renewable energy is an issue that has to be addressed in order to achieve an efficient energy system. Hydrogen has been gaining interests, as green energy carrier, which is included in the energy transition plans of not only the Netherlands, but worldwide. Due to its physical characteristics, large scale storage of hydrogen requires volumes that can only be provided by porous media in the subsurface. Underground Hydrogen Storage (UHS) in depleted gas fields is a large scale storage possibility that is generating attention and increased research. However, it is currently in a Low Technology Readiness Level, meaning that more research, and especially field scale projects are necessary. There is very few literature that tries to use alternative gases as a cushion gas for a UHS. Therefore, this investigation is relevant for the future development of UHS. This investigation will use CMG GEM, a commercial compositional reservoir simulator to model the fluid interactions in the subsurface when hydrogen is stored in depleted gas fields. This will be done by means of a sensitivity analysis, where the hydrodynamic behaviour between hydrogen and possible alternative cushion gases, such as methane, carbon dioxide and nitrogen are studied. Apart from the technical analysis, a simplified economic evaluation is used to calculate a levelized cost to store hydrogen, which will allow for an economic optimized selection of cushion gases in an UHS. The two main constraints for an UHS system are the purity of the extracted hydrogen and the rate at which it is extracted from the subsurface. The results of this investigation show that the mixing of hydrogen with an alternative cushion gas will change drastically based on the degree of the reservoir heterogeneity and the location of the perforated interval. This ever-increasing mixing will have an effect on the capability of the system of delivering pure hydrogen for the expected time.

The Dutch Government is aiming for a CO2 neutral energy supply in 2050; this requires a transition from using energy from fossil fuels to using renewable energy sources. Decline in oil production in the Netherlands occurs in an epoch with an increased interest in geothermal heat production as an alternative source of energy. In the present study it is investigated how oil production from stranded fields (fields abandoned when field development was considered not to be profitable), especially those with heavy oil, can add value to a geothermal project when thermally-enhanced oil recovery (EOR) with injection of hot water from a geothermal reservoir into an oil reservoir and coproduction of oil and geothermal energy is considered. The main focus is on the oil reservoir, while productivity and temperature of the geothermal source is assumed to be constant. In order to determine the feasibility of such project, a geological model for an oil reservoir was constructed, taking the Moerkapelle field as a case study, so that reservoir simulations can be performed on it and results in terms of oil production, heat production, total energy production and economics can be obtained and analyzed. Geological modelling (structural and stratigraphic) and reservoir simulation are developed in three different stages, every time making the model more complex (i.e. heterogeneity due to structural and sedimentary features). Project feasibility was calculated in terms of the percentage of reduction on the required subsidy for a geothermal project (required subsidy is the one that makes the NPV of a geothermal project to be zero under a pre-royalty pre-tax framework). For a homogeneous reservoir the reduction in required subsidy for a single doublet geothermal project can reach 85% and complete subsidy independence can be achieved when scaling up the project to 3 or more doublets. However, for heterogeneous reservoirs, the subsidy reduction for a single doublet geothermal project would not be higher than 52% in the most optimistic case and, when all the realizations are taken into account, there is no added value from the synergy but still an average reduction in the NPV of 13%. Scaling up the project to 3 or more doublets generates an average reduction of 31% in the required subsidy with a maximum reduction of 73% in the most optimistic case.