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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 56381 (06)
- University: Sharif University of Technology
- Department: Chemical and Petroleum Engineering
- Advisor(s): Mahani, Hassan; Zivar, Davood
- Abstract:
- Due to environmental concerns about fossil fuels energy sources, countries are striving to replace fossil fuels with renewable energy sources. However, most alternative energy sources are highly dependent on weather and seasonal conditions. Underground hydrogen storage (UHS), unlike carbon dioxide storage which only experiences the gas injection phase, involves injection and production cycles. Therefore, it faces different challenges, each of which has different effects on the final hydrogen recovery rate and, consequently, cost estimation. Some of the major challenges ahead include the reservoir structure, heterogeneity of reservoirs, selection of suitable cushion gas, the impact of the hysteresis phenomenon due to the cyclic nature of the hydrogen storage project, the solubility, and mixing of hydrogen gas with cushion gases, which result in hydrogen loss. Therefore, the aim of this research was to investigate the significant challenges associated with UHS on a reservoir scale. The CMG-GEM software was used for this purpose. Initially, the simulator inputs were improved based on hydrogen-water properties. Then, various reservoir structures and heterogeneity distributions were designed. In the next stage, the sensitivity analysis was conducted on the flow functions of hydrogen and water as the most effective functions of flow. Considering the use of different gases as cushion gas, the selection of the best gas and gas mixing are crucial, and therefore, a part of the research focuses on examining the presence of various cushion gases. Furthermore, due to the cyclic nature of hydrogen storage operations, the phenomenon of gas hysteresis becomes highly significant. Thus, in a substantial part of the project, the effect of various residual gas saturations, along with different porosities and permeabilities of the reservoir rock, and different reservoir structures, were studied. The reservoir's geometric structure plays a determining role in the placement of wells in the reservoir and, consequently, the patterns of hydrogen gas injection and production, which can significantly impact the ultimate hydrogen recovery. The results of this study indicate that the nonpolar nature of hydrogen molecules reduces hydrogen solubility in water, which can have a positive role in the final hydrogen recovery due to the cyclic nature of UHS. It is found that the flow function plays a crucial role, as 120% difference in cumulative water production was observed from changing one flow function to another. The cushion gas type substantially impacts the final efficiency of the operation and hydrogen purity in the production stream. The solubility of cushion gases in the reservoir fluids (such as carbon dioxide) and their release during production, along with their mixing with hydrogen, decrease the purity of the produced hydrogen (approximately 0.1-0.3 times gas produced in the first cycle). The results also show that a low reservoir porosity and permeability leads to trapping a significant amount of hydrogen in the reservoir and restricting the injection and production rate of hydrogen. However, increasing the size of pores (to increase the permeability and porosity of the reservoir rock) reduces the effect of the hysteresis phenomenon on the final hydrogen recovery, where the hysteresis effect is approximately 30% in larger pores compared to smaller ones. It is also observed that with an increase in the number of injection and production cycles, the hydrogen recovery efficiency decreases over time. Considering the reservoir model, the reservoir structure and well placement relative to reservoir boundaries will impose limitations on injection-production rates and hydrogen recovery efficiency. The results of this study will have practical implications for the proper selection of field structure, cushion gas type, and optimal management of hydrogen storage and production at a field scale
- Keywords:
- New Energies ; Underground Hydrogen Storage ; Hysteresis ; Cyclic Injection ; Hydrogen Producing ; Mixing ; Field Scale ; Reservoir Heterogeneity
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