天然气水合物沉积物分解过程中本构关系研究

天然气水合物具有储量大、分布广泛、清洁燃烧等优点,近年来受到研究人员的广泛关注。为了实现天然气水合物资源的安全高效开采,对其沉积层的力学稳定性进行系统评估是十分必要的。本研究在实验室内重塑了40%孔隙度的天然气水合物沉积物试样,并基于力学实验设备,对其在不同围压条件下分解过程中的力学强度及变形进行了一系列测试,获取了相应的应力应变数据。研究结果表明,水合物分解会造成沉积层强度的降低。此外,基于实验数据,在借鉴土力学邓肯-张本构模型的基础上,考虑了围压及分解时间对沉积物力学特性的影响,本文构建了适用于不同围压条件下天然气水合物沉积物分解过程中的本构模型,研究结果表明,该模型可以较好地模拟沉积物试样在分解过程中的应力应变关系,可为实现天然气水合物的安全开采提供一定的理论依据。

A Constitutive Model of Hydrate-Bearing Sediments Considering the Hydrate Dissociation

Natural gas hydrate has the advantages of large reserves, wide distribution and clean combustion. In recent years, it has attracted a wide spread attention. In order to realize the safe and efficient exploitation of natural gas hydrate, it is necessary to systematically evaluate the mechanical stability of hydrate-bearing sediments. In this paper, the methane hydrate-bearing sediments with 40% porosity were remoulded firstly, and based on the laboratory equipment for mechanics experiments, under the conditions of different confining pressures, a series of triaxial compression tests were performed. The strength and deformation characteristics of the sediments during hydrate dissociation were obtained, and the corresponding stress-strain curves were drawn. The results showed that the decomposition of natural gas hydrate can lead to the reduction of the sediments strength. In addition, based on the experimental data and the Duncan-Chang constitutive model, considering the influence of confining pressure and the dissociation time, a constitutive model of the sediment samples in the process of decomposition was constructed. This model could well simulate the stress-strain relationship of the sediments during the hydrate dissociation, providing the theoretical references to evaluate the stability of gas hydrate reservoirs.