Influence of hydrate dissociation on the stability of Arctic marine sediments

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The Arctic will experience dramatic rises in temperature over the next few decades. This will lead to the dissociation of methane gas hydrate, an ice-like material, which resides in the sediments along the continental margin, leading to increased risk of slope instability. Assessing the risk factors associated with the dissociation of natural gas hydrate requires a fundamental understanding of the geomechanical behavior of hydrate-bearing sediments. At present, predicted sediment behavior has been predominantly based on laboratory testing, due to the extreme difficulty in recovering naturally occurring hydrate-bearing sediments for testing. The data derived from laboratory tests is almost entirely based on hydrates in sands, where the hydrate is uniformly distributed throughout the pore space of the sand and increases material strength and stiffness. Numerous geomechanical and pore-physics models have been proposed based on this data to estimate changes in sediment properties, during hydrate dissociation, based on simplified assumptions of changes in sediment pore pressure, volume and stress conditions. However, hydrate morphology has been shown to exhibit a variety of forms, such as a cementing, grain supporting or pore filling, depending on the formation process adopted, giving rise to large variations in predicted sediment strengths. Arctic sediments, in contrast are comprised of mainly clay, with hydrate typically exhibiting grain-displacing behavior, where the hydrate may form as discrete nodules, fractures or layers within the clay. Therefore, assessing slope instability induced by hydrate dissociation maybe wholly inappropriate using current geomechanical models based on experimental data from hydrate-bearing sands.The research proposal will involve a series of laboratory tests on a range of materials, representative of Arctic hydrate-bearing sediments, to explore the influence of hydrate dissociation on sediment behavior. To achieve this aim novel hydrate formation methods will be developed to allow controlled formation of hydrate in clay rich sediments, which mimic the fracture morphology of typical hydrate bearing sediments, and subsequently tested to investigate a number of potential mechanisms for the influence of hydrate dissociation on sediment failure. The results from the experimental program will be used to develop more appropriate theoretical models for assessing slope stability in light of the observed changes in sediment behavior. Initially the data will be used to validate and improve existing constitutive models, which predict material behavior. This will then lead on to the development of numerical models, in a unified approach, to help address some of the shortcomings that currently exist in relation to estimating the occurrence and timing of slope instabilities triggered, or exacerbated, by gas hydrate dissociation. The outcomes of the research will provide a valuable resource for assessing slope instability of Arctic marine sediments, which is required for the successful development of the North in a safe, sustainable and environmentally friendly manner. In addition, the research will also help identify the potential methane release from gas hydrates and assess its role in future climate change. Finally, the research will provide Canada with trained engineers with skills that are highly desirable both in academia and industry.