天然气水合物沉积物等效变弹性模量损伤本构模型

Damage constitutive model of equivalent variable elastic modulus for gas hydrate sediments

准确描述水合物沉积物的变形规律和力学性质是经济安全开发天然气水合物资源的重要前提。天然气水合物沉积物受到有效围压和水合物含量等多种因素的影响从而表现出应变软化和应变硬化两种力学特性。为精确描述其变形特性,基于复合材料细观力学混合率理论和岩石孔隙损伤理论,考虑岩石统计损伤,考虑水合物含量、围压和沉积物内部孔隙变化对天然气水合物沉积物力学性质的影响,结合水合物沉积物的微元强度统计分布规律,建立了天然气水合物沉积物等效变弹性模量损伤本构模型,并建立了全部参数的确定方法。与已有实验研究结果对比表明,该模型不仅可以很好描述水合物沉积物的变形规律和力学特性,且具有模型参数易于确定、便于使用的优点。所建模型可用于水合物沉积物破碎工艺选择中的破碎模拟和破碎成孔中的孔稳定性分析评估,对非成岩天然气水合物的经济安全开采具有一定推动作用。

Accurately describing the deformation laws and mechanical properties of hydrate sediments is an important prerequisite for the economical and safe development of natural gas hydrate resources.The methane hydrate bearing sediments are affected by many factors such as effective confining pressure and gas hydrate content,thus showing two mechanical properties,i.e.,strain softening and hardening.In order to accurately describe its deformation characteristics,based on theories of the micromechanics mixing rate of composite and the rock pore damage theory,considering the statistical damage of rock,considering the influences from gas hydrate content,confining pressure and pore changes in sediments on the mechanical properties of methane hydrate bearing sediments,and combined with the statistical distribution of the micro-unit strength,the damage constitutive model of equivalent variable elastic modulus for methane hydrate bearing sediments was established,and the determination method of all parameters was established.Compared with the experimental results,it is shown that this model not only can well describe the deformation laws and mechanical properties of methane hydrate bearing sediments,but also has advantages in easy determination and simple use of the model parameters.The model proposed in this paper can be applied to simulate the crushing process of methane hydrate bearing sediments,and also analyze and evaluate the borehole stability,which is helpful to promote the economical and safe exploitation of non-diagenetic natural gas hydrate.