Influence of hydrate dissociation on the stability of Arctic marine sediments

水合物解离对北极海洋沉积物稳定性的影响

• 批准号: RGPIN-2014-04921
• 负责人: Priest, Jeffrey
• 金额: $ 1.75万
• 依托单位: University of Calgary
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=636215
• 关键词: Influence; hydrate; dissociation; stability; Arctic

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.

在接下来的几十年中，北极将体验到温度的急剧上升。这将导致甲烷气水合物（一种冰状材料）的解离，该材料位于大陆边缘的沉积物中，从而增加了斜坡不稳定性的风险。评估与天然气水合物解离相关的危险因素需要对含水液沉积物的地质力学行为有基本的理解。目前，由于实验室测试，预测的沉积物行为主要基于实验室测试，这是由于难以恢复天然存在的水合含水沉积物进行测试。源自实验室测试的数据几乎完全基于沙子中的水合物，在沙子中，水合物均匀地分布在整个沙子的孔隙空间中，并增加了材料的强度和刚度。基于这些数据，基于在水合解离期间，基于对沉积物孔隙压力，体积和应力条件的变化的简化假设，已经提出了许多地质力学和孔隙物理学模型，以估计沉积物特性的变化。然而，根据采用的地层过程，水合形态已显示出各种形式，例如胶结，谷物支撑或孔隙填充，这会导致预测的沉积物强度的差异。相比之下，北极沉积物主要由粘土组成，水合物通常表现出晶粒置换行为，其中水合物可能形成为离散的结节，裂缝或粘土中的层。因此，根据水合分解诱导的斜率不稳定性，使用当前的地质力学模型基于来自含水合的含水层的实验数据而完全不适当。该研究建议将涉及一系列对北极水合含水沉积物的实验室测试，这些实验室测试代表了含有北极水合的含水沉积物的代表，以探索水合对沉淀物行为的影响。为了实现这一目标，将开发出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，这模仿了典型的水合轴承沉积物的断裂形态，并随后进行了测试，以研究多种潜在的水合物对沉积物对沉积物衰竭影响的潜在机制。实验计划的结果将用于开发更合适的理论模型，以根据观察到的沉积物行为的变化来评估斜率稳定性。最初，数据将用于验证和改善现有的本构模型，以预测材料行为。然后，这将导致以统一的方法的发展发展数值模型，以帮助解决与估计通过气体水合离解触发或加剧的坡度不稳定性的发生和时机有关的一些缺陷。该研究的结果将为评估北极海洋沉积物的坡度不稳定提供宝贵的资源，这是以安全，可持续和环保的方式成功发展北方所必需的。此外，该研究还将有助于确定气体水合物中潜在的甲烷释放，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受过训练的工程师的技能，这些技能在学术界和行业中都非常可取。