含天然气水合物土微观力学特性研究进展

天然气水合物作为一种资源储量大、分布范围广、能量密度高的清洁能源, 受到了国内外的广泛关注, 竞相研究安全高效、持续可控的开采方法. 充分掌握含天然气水合物土的力学特性并厘清其在开采过程中的动态演化规律, 是实现天然气水合物资源产业化开发的重要前提. 含天然气水合物土的力学响应行为本质上是其内部结构演化的宏观反映, 相关的微观力学特性研究对于深化含天然气水合物土力学特性认识具有重要的意义. 本文从天然气水合物晶体、天然气水合物与土颗粒界面、含天然气水合物土3个尺度对含天然气水合物土微观力学特性的研究现状进行了总结, 系统归纳了天然气水合物的晶体结构类型及天然气水合物的孔隙微观赋存模式; 重点介绍了计算机断层扫描、扫描电子显微镜、X射线衍射及原子力显微镜等微观测试技术原理与特点; 简述了与计算机断层扫描联用的三轴剪切实验、颗粒流程序模拟及分子动力学模拟在天然气水合物微观力学特性研究方面的最新进展; 综合现有研究结果对含天然气水合物土内颗粒界面剪切机理及微观力学理论模型进行了概述分析; 最后探讨了含天然气水合物土微观力学研究目前仍存在的不足与挑战, 并给出了针对性的建议以期促进含天然气水合物土的力学特性研究发展. 

ADVANCES IN MICROMECHANICAL PROPERTIES OF HYDRATE-BEARING SOILS

As one kind of clean and unconventional energy resources, natural gas hydrates have drew enormous interests worldwide due to their high energy density, large reserves, and wide distribution in nature, and lots of countries have tried their best to develop suitable methods for gas hydrate production with acceptable safety, efficiency, continuity, and controllability. Industrialized production of gas hydrates basically needs to deeply understand mechanical properties of hydrate-bearing soils and fully clarify how these mechanical properties evolve during gas hydrate production. Mechanical properties of hydrate-bearing soils are inherently governed by their micro structures inside, and great efforts have been made to study macro mechanical properties of hydrate-bearing soils from the micro perspective, which is of great significance to deep understandings of how mechanical properties of hydrate-bearing soils evolve during gas hydrate production. In this study, advances in mechanical properties of gas hydrate crystal, interface cementation between gas hydrate and soil particles, and bulk hydrate-bearing soils are summarized. Gas hydrate crystal structures and pore-scale hydrate morphologies in hydrate-bearing soils are briefly introduced. Then, fundamental principles and advantages of microscopic testing techniques such as computed tomography (CT), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and atomic force microscopy (AFM) applied to mechanical property characterizations are emphasized. Then, up-to-date researches performed by using triaxial shearing tests combined with CT, particle flow code (PFC) and molecular dynamics (MD) numerical simulations are reviewed, and the shearing mechanism as well as constitutive models of hydrate-bearing soils are analyzed. At last, challenges in current studies on micromechanical properties of hydrate-bearing soils are discussed, and corresponding suggestions are subsequently proposed to further studies on mechanical properties of hydrate-bearing sediments.