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.

In this work, an efficient compositional framework is developed to simulate CO2 storage in saline aquifers with complex geological geometries during a lifelong injection and migration process. The novelty of the development is that essential physics for CO2 trapping are considered by a parametrization method. The numerical framework considers essential hydrodynamic physics, including hysteresis, dissolution and capillarity, by means of parameterized space to improve the computation efficiency. Those essential trapping physics are translated into parameterized spaces during an offline stage before simulation starts. Among them, the hysteresis behavior of constitutive relations is captured by the surfaces created from bounding and scanning curves, on which relative permeability and capillarity pressure are determined directly with a pair of saturation and turning point values.On the other hand, the new development allows for simulation of realistic reservoir models with complex geological features by implementing in corner point gird. The extension to corner point grid is validated by comparing simulation results obtained from the cartesian box and the converted corner-point grid of the same geometry, and it is applied to a field scale reservoir eventually. A set of sensitivity analysis reveals the roles of various physical effects and their interactions in CO2 trapping in a realistic reservoir model, apart from the investigation on the impact of migration path, linear trapping coefficient and depth. The results show the proposed compositional framework casts a promising approach to predict the migration of CO2 plume, and to assess the amount of CO2 trapped by different trapping mechanisms in realistic field-scale reservoirs.

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 project is part of the larger REX-CO2 project, which assesses the re-usability of abandoned wells in reservoirs targeted for CCS operations. It comes as a necessity to also assess the abandoned wells that will not be re-purposed, by assessing the risk they pose in terms of allowing the stored CO2 to resurface across them, which is the focus of this work. In order to assess these wells, a decision making framework was developed that will consider the main mechanisms that can lead to leakage across an abandoned wellbore. The objective is that this framework could be used by an operator of a prospective reservoir for a CCS project, prior to the start of the operations, in order to understand the risk associated with the abandoned wells present, and take decisions for remediation if necessary and possible. This framework considers three main aspects relevant for the formation of leakage paths. These are the effectiveness of the abandonment process itself, the chemical processes that can lead to the degradation of the isolation elements, and the mechanical processes that can lead to loss of integrity. The framework consists of two main parts. The first is a qualitative analysis, based on a thorough literature review, assessment of experts and testing with case studies. This qualitative assessment consist of decision trees, formed by a series of questions which answers will dictate the final outcome that will reflect the state of the abandonment. The second part is a quantitative risk analysis. For this purpose "Bayesian Belief Networks" are used which is a probabilistic tool used for calculating the relative probability of a combination of factors. The BBNs are constructed and populated based on a thorough literature review including data on experimental results. In addition, geomechanical simulations were carried to populate these models. All this data was processed and converted into normal random distribution functions, which were used to infer the probabilities that would be included in the BBNs. The final outcome of the BBNs reflect the probability for leakage to occur. Both the qualitative and quantitative parts of the framework are integrated together in order to obtain a complete analysis. The complete framework was tested with case studies based on real wells for which the abandonment states are known and reported by the operator, to observe how the outcome of the framework analysis matched the outcomes of the analysis performed by the operator. With this study, a complete and systematic framework was developed that can be used to aid decision making for prospective CCS projects in the future. The framework is constructed such that it has the capacity to be improved and expanded in the future, to increase its consistency and broaden its applications. A series of potential improvements are also explained at the end of this report. Furthermore, the framework can be used to challenge the current abandonment standards and assess what will have to be changed to adapt the current abandonment techniques so that they include CCS projects.

Underground hydrogen storage (UHS) in porous reservoirs offers a promising solution for addressing the temporal and spatial variability of renewable energy sources. To safely and efficiently utilize these reservoirs for UHS at an affordable cost, it is essential to understand the diverse disciplines involved at various scales. This study combines large-scale techno-economic evaluations with micro- scale laboratory research to assess the commercial and technical viability of UHS in porous media. A techno-economic case study of commercial-scale UHS in a depleted gas field in the Dutch nearshore is investigated, defining the integrated scope of infrastructure and facilities and estimating associated costs. Additionally, the multiphase flow behavior and redistribution of hydrogen in sandstone rock are analyzed through experimental assessment of relative permeability, capillary trapping, dissolution, and Ostwald ripening using CT imagery. The case study compares various surface facility design concepts, revealing that the Levelized Cost of Hydrogen Storage (LCOHS) ranges from [cannot be disclosed for confidentiality reasons] , depending on the required purification scope of the production stream. Cushion gas cost significantly impacts the LCOHS. The multiphase flow behavior was examined on a micro-scale by co-injecting hydrogen and brine at varying fractional flows into a vertically placed 17 cm Berea sandstone rock sample at 25°C and 50 bar, while observing under CT imaging during both drainage and imbibition. High- resolution CT imaging visualized Ostwald ripening at the pore scale after several periods without flow. The experimental results indicate a hydrogen end-point relative permeability of 0.043 and a linear trapping coefficient of 0.725. No preferential flow paths were observed, however, dissolution was shown to have an impact the saturation profiles. Pore-scale image analysis demonstrated that Ostwald ripening leads to the fragmentation of mid-sized hydrogen ganglia and the growth of larger ganglia over time. These findings provide valuable insights into optimizing UHS and provide input for large-scale reservoir simulations, emphasizing the importance of integrating techno-economic assessments with detailed laboratory research for the commercial success of UHS.

Underground hydrogen storage (UHS) in porous reservoirs offers a promising solution for addressing the temporal and spatial variability of renewable energy sources. To safely and efficiently utilize these reservoirs for UHS at an affordable cost, it is essential to understand the diverse disciplines involved at various scales. This study combines large-scale techno-economic evaluations with micro- scale laboratory research to assess the commercial and technical viability of UHS in porous media. A techno-economic case study of commercial-scale UHS in a depleted gas field in the Dutch nearshore is investigated, defining the integrated scope of infrastructure and facilities and estimating associated costs. Additionally, the multiphase flow behavior and redistribution of hydrogen in sandstone rock are analyzed through experimental assessment of relative permeability, capillary trapping, dissolution, and Ostwald ripening using CT imagery. The case study compares various surface facility design concepts, revealing that the Levelized Cost of Hydrogen Storage (LCOHS) ranges from [cannot be disclosed for confidentiality reasons] , depending on the required purification scope of the production stream. Cushion gas cost significantly impacts the LCOHS. The multiphase flow behavior was examined on a micro-scale by co-injecting hydrogen and brine at varying fractional flows into a vertically placed 17 cm Berea sandstone rock sample at 25°C and 50 bar, while observing under CT imaging during both drainage and imbibition. High- resolution CT imaging visualized Ostwald ripening at the pore scale after several periods without flow. The experimental results indicate a hydrogen end-point relative permeability of 0.043 and a linear trapping coefficient of 0.725. No preferential flow paths were observed, however, dissolution was shown to have an impact the saturation profiles. Pore-scale image analysis demonstrated that Ostwald ripening leads to the fragmentation of mid-sized hydrogen ganglia and the growth of larger ganglia over time. These findings provide valuable insights into optimizing UHS and provide input for large-scale reservoir simulations, emphasizing the importance of integrating techno-economic assessments with detailed laboratory research for the commercial success of UHS.