基于颗粒重组理论的水合物沉积物温-压耦合热力学模型

Thermodynamic model of coupled temperature and pressure effects for hydrate-bearing sediments within particle rearrangement theory

水合物沉积物赋存时的温度和孔隙水压变化对沉积物的力学性质影响明显。基于颗粒重组理论,通过引入温-压耦合系数δ、剪应变和体应变胶结应力衰减方式(λ_(v),λ_(s))和水合物饱和度影响下的剪胀方程d,建立了水合物沉积物温-压耦合热力学模型。利用数值模拟结果同室内试验结果的对比分析,从宏观力学性质变化和微观作用机理两个角度探讨了围压、水合物饱和度和温-压耦合系数对沉积物力学特性的影响。最后,对模型中的刚度系数和体应变衰减参数进行敏感性分析。结果表明:引入温-压耦合系数的水合物沉积物模型能够很好的描述沉积物赋存的温度和水压同其力学特性变化关系。环境温度降低和水压增大增强了微观层面水合物的胶结强度和刚度,宏观表现为峰值强度、应变软化和剪胀性提高。刚度系数γ通过增大沉积物初始刚度使得沉积物表现出更强的峰值强度。体应变衰减参数λ_(v)通过提高胶结应力衰减速率增强沉积物的应变软化特性。

The mechanical properties of hydrate-bearing sediments are significantly influenced by changes in temperature and water pressure.Based on the particle rearrangement theory,a thermodynamic model that couples temperature and pressure,incorporating the dilation equation considering the effects of hydrate saturation and introducing the bond degradation parameters caused by shear and volumetric strains,is developed to describe the mechanical behaviors of hydrate-bearing sediments.The numerical simulation results are compared with the laboratory experiments to explore the effects of confining pressure,hydrate saturation and the temperature-pressure coupling coefficient on the mechanical properties of sediments from both macroscopic and microscopic perspectives.Finally,the sensitivity analyses are conducted on the stiffness coefficient and bond degradation parameter.The results indicate that the introduction of a temperature-pressure coupling coefficient in the model effectively describes the relationship between the mechanical properties of sediments and temperature and water pressure during deposition.Decreasing environmental temperature and increasing water pressure enhance the bond strength and stiffness of hydrates at the microscopic level,resulting in the increased peak strength,strain softening and shear dilation at the macroscopic level.Increasing the stiffness coefficient γ enhances the peak strength of sediments by increasing the initial stiffness of sediments.The bond degradation parameter enhances the strain-softening behaviors of sediments by increasing the rate of bond degradation.