开采扰动下含天然气水合物土的弱化机理与规律研究

Discovering the change laws for shear strength of gas hydrate-bearing soils under disturbance of exploration is one of the key problem that should be solved during analyzing the field stabilization in exploring gas hydrate. So far researchers lack profound and systematic insight into the change laws of weakening of disturbed gas hydrate-bearing soils, hindering the stability analysis for the gas hydrate-bearing layers under the exploring disturbance. This project firstly plans to realize the key technology of nondestructive detection for gas hydrate content during mechanical tests, and then integrate it into the triaxial and direct shearing tests. Shear strength and shear modulus of gas hydrate-bearing soils under the simulated condition of exploring would be tested by traxial and direct shear equipments self-devoloped, detecting shear wave velocity using the bend element system, discovering the behavior of strength of gas hydrate-bearing soils under the condition of exploring,and found a model or the shear strength. The relationship between the content of gas hydrate, temperature and pressured in is to be studied by NMR and found the phase equilibrium model for gas hydrate-bearing soils; On these basis, to reveal the weakening mechanism and laws of gas hydrate-bearing soils under disturbance of exploration,and establish a theoretical model for describing the weakening process of gas hydrate-bearing soils .This study is not only helpful to the insight into the change laws of mechanical parameters for exploring disturbed gas hydrate-bearing soils, but also could supply theoretical and technological support for preventing and controlling induced geological hazard and engineering accidents during gas hydrate exploration and optimizing exploring schemes as well.

揭示含天然气水合物土强度变化规律是含水合物地层稳定分析中必须解决的关键问题。研究表明，开采扰动将对含水合物土产生显著的弱化作用。目前国内外对开采扰动下含天然气水合物土的弱化机理与规律缺乏深入认识，制约了开采扰动下场地稳定性的分析研究。本项目拟通过解决水合物含量与力学特性试验一体化的关键技术，模拟温度与压力变化下的直剪与三轴试验、基于弯曲元的剪切波速测试，揭示开采扰动下含水合物土强度特性的变化规律，建立可反映温度-气压变化的强度理论模型；利用核磁共振技术，研究开采扰动下含天然气水合物土三相物质转化与平衡关系特征，建立水合物含量与温度-压力的平衡关系模型；在此基础上，揭示开采扰动下含水合物土的弱化机理与规律，建立可描述开采扰动下含水合物土弱化过程的理论模型。本研究不仅有助于认识开采扰动下含天然气水合物土的力学特性变化规律，还可为防治水合物开采诱发的工程地质灾害、优化开采方案提供理论和技术支持。

天然气水合物是一种潜力巨大的战略性替代能源, 由于目前对含水合物土的物理力学特性认识尚不充分，尤其是开采扰动下含天然气水合物土的弱化机理与规律缺乏深入研究，制约了天然气水合物大规模开发利用。本项目围绕开采扰动下含天然气水合物土的弱化规律与机理，重点开展了含天然气水合物土物理力学参数的关键测试方法与仪器研制、强度变形测试以及理论建模和数值分析等方面的研究工作。成功研制了多功能水合物三轴试验系统和含天然气水合物土直剪仪，利用自行研制的设备开展了水合物三轴与直剪的实验测试分析，研究了含天然气水合物土的强度与变形随水合物含量变化规律，提出了含天然气水合物土强度随水合物含量变化的关系模型与本构模型；利用核磁共振技术对二氧化碳水合物在砂中生成和分解进行了核磁共振弛豫测试，探索出利用核磁共振技术对水合物在砂土中的形成分解过程的测试技术，并提出了一种基于核磁共振弛豫测试的含水合物土的定量和表征方法；采用建立的本构模型对简化的采气模型进行了数值模拟计算，对降压开采条件下的地层沉降进行了预测。研究成果可为防治水合物开采诱发的工程与地质灾害问题、优化开采方案等提供理论依据和技术支持。