Hydrates in sediments : their role in wellbore/casing integrity and CO2 sequestration
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Gas hydrates have attracted much interest among researchers recently because of their wide range of applications. The impact of natural gas hydrates in subsea sediments on the development of conventional hydrocarbon reservoirs in deep offshore and the potential role of CO2 hydrates as a secondary safety factor in subsurface storage of CO2 are the key areas in this thesis. Several experiments were conducted on synthetic samples containing methane hydrate with different hydrate saturations to measure their geophysical properties, mechanical properties and understand their mechanical behaviour at realistic conditions. A numerical model was also developed with ABAQUS (a finite element package) to investigate the casing stability of the wellbore drilled in gas hydrate bearing sediments in deep offshore environments using the measured properties of gas hydrate bearing sediments under different scenarios. The role of hydrates in subsurface storage of CO2 was studied using a unique experimental set-up by simulating geothermal temperature gradient. The objective was to investigate whether CO2 leaked from subsurface storage sites can be converted into hydrates, providing a secondary seal against further CO2 leakage to ocean/atmosphere.