【作者】 宋琪；

【导师】 刘卫国；

【作者基本信息】 大连理工大学 ， 动力工程（专业学位）， 2023， 硕士

【摘要】 天然气水合物作为一种新型能源,以其储量大、分布广、能量密度高而受到全球的广泛关注。泥质粉砂沉积物中存在大量的天然气水合物资源,然而水合物的开采会导致含水合物沉积物变形,甚至发生海底滑坡等地质灾害。因此,全面了解含水合物沉积物的力学特性是实现水合物储层安全高效开采的关键。迄今为止,大多数研究均基于各向同性固结这一简化条件下进行的,然而,研究各向异性条件下的水合物沉积物力学特性更有利于解释其实际强度与变形特性。本文主要开展了在不同有效围压和饱和度条件下固结应力比对水合物沉积物力学特性的研究,探究了固结应力比对水合物沉积物力学特性影响规律,为水合物安全高效开采提供了数据及理论支撑。首先,对南海神狐海域海洋土壤进行了粒度分析,得到粒径级配及主要成分并绘制了三相图,分析发现海洋沉积物土壤属于泥质粉砂,非均匀性系数为9.19,曲率系数为1.11,粒径级配良好;搭建了一套低温高压三轴实验系统,能够满足水合物沉积物变形过程原位力学测试。其次,开展了不同有效围压下固结应力比对水合物沉积物力学特性影响的实验研究,发现各向异性对水合物沉积物力学特性的影响规律,在相同固结应力比条件下,有效围压的增大能够促进应变硬化及剪缩;固结应力比的增大会抑制应变硬化及剪缩,提高水合物沉积物破坏强度、刚度及内聚力,降低内摩擦角及破坏体变;固结应力比增加能够促使土颗粒互锁,偏应力增加,并抑制剪切变形,最终导致破坏强度、弹性模量随固结应力比增加而增加;建立了沉积物刚度、内聚力及内摩擦角与固结应力比及有效围压的数学关系式。最后,开展了不同水合物饱和度下固结应力比对水合物沉积物力学特性影响的实验研究,发现在相同固结应力比条件下,水合物饱和度的增大能够促进应变硬化及剪缩;无论是各向同性还是各向异性固结条件下,水合物饱和度的增大均能够提高破坏强度及弹性模量;在各向同性固结条件下破坏体变与水合物饱和度呈负相关,而在各向异性固结条件下破坏体变与水合物饱和度呈正相关。更多还原

【Abstract】 As a new type of energy source,natural gas hydrates have received widespread attention worldwide for their large reserves,wide distribution and high energy density.A large amount of natural gas hydrate exists in clayey-silty sediment.However,hydrate mining can lead to deformation of hydrate-bearing sediments and even geological disasters such as submarine landslides.Therefore,a comprehensive understanding of the mechanical properties of HBSs is the key to achieve safe and efficient extraction of hydrate reservoirs.Up to now,most studies have been carried out based on the simplified condition of isotropic consolidation.However,it is more helpful to study the mechanical properties of hydrate sediments under anisotropic conditions to explain their actual strength and deformation characteristics.In this paper,we investigate the influence of consolidation stress ratio on the mechanical properties of HBSs under different effective confining pressure and saturation conditions,and provide data and theoretical support for safe and efficient hydrate mining.Firstly,the particle size analysis of marine soil in the Shenhu sea area of South China Sea was carried out,and the particle size gradation and main components were obtained and the three-phase diagram was drawn.The analysis found that the marine sediment soil belongs to clayey silt with non-uniformity coefficient of 9.19,curvature coefficient of 1.11 and good grain size gradation.A low-temperature,high-pressure triaxial experimental system was built to meet the in-situ mechanical testing of hydrate sediment deformation processes.Secondly,an experimental study on the effect of consolidation stress ratio on the mechanical properties of HBSs under different effective confining pressure was carried out,and it was found that the effect of anisotropy on the mechanical properties of HBSs.And the increase of effective confining pressure could promote the promotion of strain hardening and shear shrinkage under the same confining stress ratio.And the increase of consolidation stress ratio will suppress strain hardening and shear shrinkage and improve the failure strength,initial elastic modulus and cohesion of HBSs,reduce the angle of internal friction and volumetric strain of failure.It is believed that the increase of consolidation stress ratio drives the interlocking of soil particles and the increase of deviator stress,which inhibits the shear deformation and leads to the increase of failure strength and elastic modulus with the increase of consolidation stress ratio.Mathematical relations between elastic modulus,cohesion and internal friction angle and consolidation stress ratio were established.Finally,an experimental study on the effect of consolidation stress ratio on the mechanical properties of HBSs under different hydrate saturation was carried out,and it was found that under the same consolidation stress ratio,the increase of hydrate saturation can promote strain hardening and shear shrinkage.The increase of hydrate saturation can increase the failure strength and elastic modulus under both isotropic and anisotropic consolidation conditions.Under isotropic consolidation conditions,the volumetric strain of failure is negatively correlated with hydrate saturation,while under anisotropic consolidation conditions,the volumetric strain of failure is positively correlated with hydrate saturation.更多还原