层状赋存含水合物沉积物的本构模型研究

A STUDY ON THE CONSTITUTIVE MODELING OF THE INTERBEDDED HYDRATE-BEARING SEDIMENTS

推进天然气水合物资源开采是我国能源战略的重要任务。层状赋存形态的含水合物沉积物在目标开采储层中普遍存在,水合物开采引起的沉积物层扰动会直接诱发剪切变形影响储层的稳定性,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。本文采用均匀化理论,基于每层沉积物的弹塑性刚度矩阵构建层状形态代表体积单元的宏细观控制方程,建立了层状赋存含水合物沉积物的本构表征方法。代表体积单元内每层的沉积物模型参数可基于均质含水合物沉积物试样的三轴试验标定获取。通过将层状本构模型预测和层状沉积物三轴试验以及数值试验的应力-应变关系对比验证,本研究提出的层状本构模型可准确描述原位储层中层状赋存含水合沉积物的力学行为。

Advancing 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.However,the hydrate gas production process disturbs the hydrate-bearing sediment,which induces shear strain to mobilise the reservoir stability and severely restrain the safe exploitation of hydrate resources.The existing constitutive characterization of hydrate-bearing sediments is mainly based on the assumption of homogeneous and isotropic material properties,and without a proper 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 uses the homogenization theory to construct the macro and mesoscopic control equations of interbedded sediments.Based on the elastic-plastic stiffness matrix of each layer of sediments,a constitutive model for interbedded hydrate-bearing sediments was established.Sediment model parameters representing each layer within a representative volume element can be obtained based on triaxial test results of homogeneous hydrate-bearing sediment samples.By comparing the prediction results of the proposed constitutive model with the stress-strain results of the interbedded sediment triaxial test and numerical simulation,the proposed constitutive model can accurately describe the mechanical behavior of interbedded hydrate-bearing sediments in the in-situ reservoirs.