水合物降压分解致深海粉质沉积物宏微观性质演化研究

Methane hydrate is widely distributed in silty sediments in the South China Sea as significant sources of strategic green energy of China, and has been successfully trial-produced by depressurization. Macro-microscopic properties of methane hydrate-bearing sediments (MHBS) associated with hydrate dissociation control the stratum behaviour and wellbore stability, and furthermore provide theoretical basis for hydrate exploitation. Within the framework of macro and micro geomechanics, the MHBS will be artificially prepared using the silty soil from the South China Sea followed by hydrate dissociation tests and microscopic observations on the MHBS samples under different load paths and stress states to investigate the deformation behaviour, failure modes and microstructure of MHBS. Then, taking into account the characteristics of the particles and contacts of silty soils, a discrete element model will be established coupled with gas-liquid flow code to reveal the microscopic mechanisms associated with hydrate dissociation by depressurization, i.e., particle movement, microstructure and micromechanics. Finally, contact fabric evolution and bonding degradation formulations will be proposed to describe the evolutions of microstructure and micromechanics of MHBS associated with hydrate dissociation by depressurization. In summary, this research is of significant academic value and vital theoretical support on methane hydrate production in silty sediments by investigating the deformation behaviour, failure modes, microscopic mechanisms as well as the microscopic theoretical formulations of MHBS associated with hydrate dissociation by depressurization.

天然气水合物广泛赋存于南海粉质沉积物中，是我国重要的战略性绿色能源储备，目前已实现南海水合物降压试采。含水合物沉积物（能源土）的宏微观性质决定了储层力学响应和开采井稳定性，是实现水合物长期安全稳定开采的重要理论基础。项目采用宏微观相结合的研究思路，首先以南海地区储层土体为骨架制备人工能源土，运用低温高压三轴试验设备进行多种加载路径不同应力状态下的水合物降压分解试验，研究土体变形特征和破坏模式，观测土体微观结构演变；然后考虑粉质沉积物的颗粒和接触特点建立气液流-离散元耦合数值模型，从微观尺度分析水合物降压分解下土体颗粒运移、微观结构和接触力学特征；最后通过理论分析建立接触组构演化式和胶结破损演化式以表述水合物降压分解下土体的微观结构和微观力学演化特征。项目研究水合物降压分解下粉质能源土的变形特征、破坏模式及其微观机理并建立理论演化式，具有重要的学术价值并可为南海地区水合物开采提供科学依据。

天然气水合物广泛赋存于南海粉质沉积物中，含水合物粉质沉积物（粉质能源土）的宏微观性质决定了储层力学响应和开采井稳定性。项目为了研究水合物的力学作用，建立了能源土粉粒-水合物和水合物-水合物温压力耦合接触模型和水合物分解模型，进而根据粉质能源土的颗粒和接触特点，将水合物颗粒随机填充到粉粒骨架中，建立了散粒水合物能源土、团簇水合物能源土和胶结团簇水合物能源土三种理想类型的粉质能源土离散元数值模型。研究了粉质能源土在不同应力路径加载和不同水合物分解路径下的土体变形特征和破坏模式，研究了试样应力演化、体积变化、胶结破坏、配位条件和应力传递等，从微观尺度分析了加载和水合物分解下粉质能源土微观结构和接触力学特征；通过理论分析建立了加载和水合物分解下粉质能源土的胶结破损演化和水合物承载率演化规律。研究结果对建立胶结颗粒材料理论框架具有学术价值，可为粉质能源土本构模型研究提供理论基础，并为粉质地层水合物开采中的力学问题提供科学支持。