Experimental investigation of the shear strength of gas hydrate-bearing sediments

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Interest in methane gas production from hydrate accumulations has increased dramatically in the last decade, with this vast supply of unconventional gas offering a promising future energy resource. Hydrates also pose a geohazard in exploration and production of conventional offshore hydrocarbon reserves; hydrate dissociation has been linked to submarine slope instability, gas blowouts, and near well failures. Environmental implications of hydrate deposits can be negative owing to potential methane release to the atmosphere, or positive as prospective storage of carbon dioxide in hydrate form. Gas hydrates are solid crystalline compounds comprised of hydrogen-bonded water molecules forming a rigid crystal lattice stabilized by encaged gas molecules, predominately methane. Although our knowledge of the geomechanical properties of hydrate bearing sediments is immature, experimental and theoretical models demonstrate that the presence of hydrate will increase strength and stiffness and decrease permeability; however, dissociation of hydrate induces fluid and gas production, loss of strength and stiffness, and elevated pore pressures. This research is aimed at understanding the strength properties of hydrate bearing sediments. Fundamental parameters which influence strength include hydrate content, mode of hydrate occurrence, confining pressure, and initial pressure-temperature conditions; a comprehensive experimental program will be undertaken to assess these parameters. A theoretical model describing hydrate-sediment behavior will be developed and verified with the experimental data. Results arising from the proposed research will provide essential input for hydrate reservoir simulators, hydrate reservoir response during production or sequestration, and stability analyses of hydrate bearing submarine slopes. Canada has identified research on gas hydrates as a strategic target area because of their energy and geohazard importance; understanding the geomechanics, strength in particular, is critical for accurate assessments of both risks and benefits. This innovative program will make fundamental and groundbreaking advances in the global understanding of gas hydrate systems.