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

在过去的十年里，人们对从水合物堆积中生产甲烷气体的兴趣急剧增加，这种巨大的非常规天然气供应提供了一种很有前途的未来能源资源。水合物还对常规海上油气储量的勘探和生产造成地质灾害；水合物解离与海底斜坡不稳定、天然气井喷和近井故障有关。水合物沉积对环境的影响可能是负面的，因为甲烷可能释放到大气中，也可能是正面的，因为二氧化碳可能以水合物的形式储存。天然气水合物是一种固体晶体化合物，由氢键水分子组成，形成由包裹的气体分子(主要是甲烷)稳定的刚性晶格。虽然我们对含水合物沉积物的地质力学性质的认识还不成熟，但实验和理论模型表明，水合物的存在会增加强度和刚度，降低渗透率；然而，水合物的解离会导致流体和天然气的产生，强度和刚度的损失，以及孔压的增加。 本研究旨在了解含水合物沉积物的强度特性。影响强度的基本参数包括水合物含量、水合物赋存方式、围压和初始压力-温度条件；将进行全面的实验计划来评估这些参数。建立了描述水合物-沉积物行为的理论模型，并用实验数据进行了验证。拟议的研究结果将为水合物储集层模拟器、水合物储集层在生产或封存过程中的响应以及含水合物的海底斜坡的稳定性分析提供必要的输入。由于天然气水合物在能源和地质灾害方面的重要性，加拿大已将其确定为战略目标领域；了解地质力学，特别是其强度，对于准确评估风险和收益至关重要。这一创新计划将在全球了解天然气水合物系统方面取得根本性和开创性的进展。

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.