考虑含水合物沉积物损伤的多场耦合模型研究

天然气水合物是一种新型的清洁能源，具有广阔的应用前景。但在水合物开采过程中温压条件的改变会引起水合物的分解，导致含水合物沉积物胶结强度的丧失；同时，沉积物在加载过程中由于其内部微裂纹、缺陷逐渐扩展以及土颗粒间的水合物逐渐破碎也会引发含水合物沉积物的损伤，而以往对于水合物分解过程中多场耦合模型的研究忽略了沉积物结构损伤演化过程及其对耦合过程的影响。因此，基于连续损伤理论，在损伤统计本构模型中引入三参数的Weibull分布和残余强度修正系数，建立起考虑损伤阈值和残余强度影响的含水合物沉积物损伤统计本构模型；进而将本构模型嵌入到水合物分解过程的多场耦合模型中，建立了考虑含水合物沉积物损伤的温度-应力-渗流-化学（THMC）多场耦合数学模型；基于该模型讨论了含水合物沉积物结构损伤对水合物分解过程中沉积物储层的变形、压力、温度等因素的影响规律。通过计算分析发现：含水合物沉积物结构损伤对水合物分解的多场耦合过程具有显著影响，并且随着分解时间的增加，其影响逐渐增大。

Study on multi-field coupling model considering damage of hydrate-bearing sediments

Natural gas hydrate is a new type of clean energy that has broad application prospects. However, the change of temperature and pressure conditions in the process of hydrate mining will cause the dissociation of hydrate, which lead to the loss of cementation strength of hydrate-bearing sediments. Meanwhile, micro-cracks and defects in the sediments expand gradually, the hydrates between the soil particles are damaged and broken in the loading process. However, in the previous investigations of the multi-field coupling model on hydrate dissociation process, the damage evolution process of sediment structure and its influence on the coupling process are ignored. Therefore, the Weibull distribution of three parameters and residual strength correction coefficient are introduced into the damage statistical constitutive model in this paper based on the continuous damage theory, and the damage statistical constitutive model of hydrate-bearing sediment considering the influence of damage threshold and residual strength is established. And then, the constitutive model is embedded in the multi-field coupling model of the hydrate dissociation process, and the thermo-hydro- mechanical-chemical (THMC) multi-field coupled mathematical model considering damage of hydrate-bearing sediments is proposed. Finally, based on the model, the influence of sediment structural damage on the deformation, pressure and temperature of sediment reservoirs during hydrate dissociation are discussed. It can be shown from the computational results that the structural damage of hydrate-bearing sediments has a significant effect on the multi-field coupling process about the dissociation of hydrates, and its influence increases gradually with the increase of dissociation time.