层状赋存对水合物沉积物的力学特性影响机理及其本构表征

Advancing the gas hydrate exploitation is one of the most important tasks for China's future energy strategy. The interbedded formation of hydrate-bearing sediments is a common feature in many target production regions, which directly induces shear strain to mobilize the reservoir stability and restrain the safe exploitation of hydrate resources severely. The existing constitutive characterization of hydrate-bearing sediments is mainly based on the assumption of homogeneous and isotropic material properties, and without a sound constitutive characterization method to consider the strong non-linear mechanical properties of hydrate-bearing sediments affected by the interbedded formation, that leads to inaccurate estimation of the stress and strain responses of the target production region. This study will focus on the influence mechanism of the interbedded formation on the mechanical properties of hydrate-bearing sediment in the hydrate reservoir. A high-pressure low-temperature triaxial apparatus shall be used to conduct triaxial compression tests on prepared interbedded hydrate soil samples, to investigate the key influence factors on the mechanical properties and to study the evolution of mechanical properties under external loads. The constitutive model of the interbedded hydrate-bearing sediments by adopting homogenization technique shall be established, and the model parameter calibration method for the in-situ pressure cores correlating to the site well-log data shall be proposed, so that we can more accurately describe the constitutive behavior of the south China sea interbedded hydrate-bearing sediments in the reservoir. This research provides an important theoretical basis for ensuring the safe production of the hydrates gas in China.

推进天然气水合物资源开采是我国能源战略的重要任务。水合物沉积物的层状赋存形态在目标开采区域中普遍存在，会直接诱发剪切应变影响储层的稳定性，严重制约水合物资源的安全开采。现有水合物沉积物的本构表征主要基于空间均匀分布、各向同性的材料特征假设，缺少考虑水合物沉积物的强非线性力学特性受层状赋存形态影响的本构表征方法，无法准确预测目标开采储层的应力应变规律。本项目围绕储层中层状赋存形态对水合物沉积物的力学特性影响机理展开研究，拟采用高压低温三轴仪对层状赋存形态的水合物沉积物试样进行三轴压缩试验，揭示影响其力学特性的关键因素，阐明在外部荷载作用下其力学性质的演化规律，构建层状赋存含水合物沉积物的均匀化本构表征模型，提出基于测井数据的原位岩芯试样本构模型参数确定方法，以期更加准确描述我国南海原位储层中层状赋存含水合物沉积物的本构行为，为保障我国天然气水合物安全开采提供重要的理论依据。

本项目以准确描述我国南海原位储层中层状赋存含水合物沉积物的本构行为为目标，采用高压低温三轴试验和有限元数值模拟相结合的手段，揭示了层状赋存形态对水合物沉积物力学特性的关键影响因素，阐明了其在外部荷载作用下的力学性质演化规律，构建了层状赋存含水合物沉积物的均匀化本构表征模型，描述了原位储层中层状赋存含水合沉积物的本构行为，实现了准确模拟我国南海目标开采储层的应力应变规律。具体内容及相关成果如下：. （1）建立了原位储层中水合物沉积物的力学特性数据库，制备了层状赋存含水合物沉积物的三轴试样，展开了不同围压下的三轴压缩试验，研究了不同条件下三轴试样剪切破坏的应力应变规律，揭示了层状赋存形态对水合物沉积物的力学特性影响机理。. （2）阐明了在外部荷载作用下层状赋存含水合物沉积物的力学特性演化规律，引入了材料特征参数和外部动态参数，提出了均匀化本构表征方法，构建了层状赋存含水合物沉积物的本构表征模型，编译了本构模型代码并在在数值软件中实现力学行为模拟。. （3）对目标开采场地的沉积物开展了大量数值三轴试验，建立了力学行为数据集，构建了基于人工神经网络的力学行为智能预测模型，提出了基于人工神经网络和蒙特卡洛模拟的本构模型参数智能反演方法，建立了我国南海原位储层中水合物开采的数值模型，展开了数值模拟研究描述原位储层中沉积物的应力应变规律。. 通过本项目的研究，现已发表第一/通讯作者论文7篇，其中SCI检索论文5篇，EI检索论文2篇；申请授权软件著作权2项；在国际上做了相关研究的2次邀请报告，国内5次邀请报告，联合培养2名硕士研究生。项目总体超额完成了预期要求。