Influence of hydrate dissociation on the stability of Arctic marine sediments

未来几十年，北极的温度将急剧上升。这将导致甲烷气体水合物（一种存在于大陆边缘沉积物中的冰状物质）解离，从而增加边坡不稳定的风险。评估与天然气水合物解离相关的风险因素需要对含水合物沉积物的地质力学行为有基本的了解。目前，预测的沉积物行为主要基于实验室测试，因为回收天然存在的含水合物沉积物进行测试极其困难。实验室测试得出的数据几乎完全基于沙子中的水合物，其中水合物均匀分布在沙子的整个孔隙空间中，并增加了材料的强度和刚度。基于这些数据提出了许多地质力学和孔隙物理模型，以基于沉积物孔隙压力、体积和应力条件变化的简化假设来估计水合物解离过程中沉积物性质的变化。然而，水合物形态已被证明表现出多种形式，例如胶结、颗粒支撑或孔隙填充，这取决于所采用的形成过程，从而导致预测的沉积物强度存在很大变化。相比之下，北极沉积物主要由粘土组成，水合物通常表现出颗粒置换行为，其中水合物可能在粘土内形成离散的结核、裂缝或层。因此，使用基于含水合物砂实验数据的现有地质力学模型来评估水合物解离引起的边坡失稳可能完全不合适。该研究计划将涉及对代表北极含水合物沉积物的一系列材料进行一系列实验室测试，以探索水合物解离对沉积物行为的影响。为了实现这一目标，将开发新的水合物形成方法，以允许在富含粘土的沉积物中控制水合物的形成，该方法模拟典型含水合物沉积物的断裂形态，并随后进行测试以研究水合物解离对沉积物破坏影响的许多潜在机制。实验计划的结果将用于开发更合适的理论模型，根据观察到的沉积物行为变化评估边坡稳定性。最初，这些数据将用于验证和改进现有的本构模型，以预测材料行为。然后，这将导致以统一的方法开发数值模型，以帮助解决目前在估计由天然气水合物解离引发或加剧的斜坡不稳定性的发生和时间方面存在的一些缺点。研究成果将为评估北极海洋沉积物的斜坡不稳定性提供宝贵的资源，这是北方以安全、可持续和环境友好的方式成功开发所必需的。此外，该研究还将有助于确定天然气水合物潜在的甲烷释放量，并评估其在未来气候变化中的作用。最后，这项研究将为加拿大提供训练有素的工程师，这些工程师拥有学术界和工业界非常渴望的技能。

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.