| Summary: | The world needs more energy and the energy has to be more sustainable with respect to carbon dioxide (CO2) emissions. This is the backdrop for studying the diverse applications of gas hydrates in nature. The ice-like substance is found worldwide as inclusions in the pore space of subsurface sediments and may affect the global energy supply and climate profoundly: 1) The large amounts of hydrate-bound natural gas, predominantly methane gas (CH4), could provide the world with energy for decades. Global consumption of natural gas is expected to increase with 45% by 2030 (IEA, 2018b). Countries like Japan, China, India and South Korea are seeking to increase their energy security by developing natural gas production from subsurface accumulations of gas hydrates. 2) The natural affinity for CO2 to form gas hydrates in the shallow subsurface could increase the storage capacity and security of carbon sequestration. Carbon capture and storage (CCS) is the removal of CO2 from the atmosphere (or before it reaches the atmosphere) and subsequent long-term storage of the CO2 in the subsurface. The projections of the IPCC that seeks to limit global warming to 1.5°C above the pre-industrial level rely on the use of CO2 removal from the atmosphere on the order of 100 – 1000 gigatonnes of CO2 (GtCO2) during this century (IPCC, 2018). The formation of CO2 hydrates could provide a self-sealing mechanism during CO2 storage in saline aquifers which would decrease the risk of CO2 leakage considerably. In both cases, fundamental knowledge about gas hydrates in porous media is needed. The scientific work presented in this thesis contributes to the understanding of CH4 and CO2 hydrates in sediments with special emphasis on phase transitions and fluid flow in hydrate-saturated porous rock. Coupling the fluid flow with gas hydrate saturation and growth pattern is important to control the production rate of CH4 gas from CH4 gas hydrates and to model the sealing capacity of CO2 gas hydrates. The rate and distribution of fluid flow during ...
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