Abstract:

On the basis of stress sensitivity experiments, the functional relationship between effective stress and physical parameters, including permeability, porosity and elastic modulus, was established. Meanwhile, combined with the existing models for the relationship between physical parameters of reservoirs and the hydrate saturation, a comprehensive model was established to describe dynamic variations of physical parameters of hydrate reservoirs. This model took into full account of the effect of hydrate dissociation and the influence of stress state variations in reservoirs on physical parameters. The case study on the natural gas hydrate production by decompression demonstrated that effects of hydrate dissociation and the reservoir stress sensitivity were two important influencing factors on physical parameters of hydrate reservoirs. Of which the effect of hydrate dissociation was the controlling factor that made the permeability and porosity of hydrate reservoirs in the dissociation area increase obviously and the elastic modulus decrease dramatically. The influence of the reservoir stress sensitivity occurred in the whole sweep area of pressure, and it played a certain inhibiting role on the impact of hydrate dissociation because its effect on physical parameters was contrary to that of hydrate dissociation, therefore, it should never be ignored.

Key words: gas hydrate reservoir, physical parameter, dissociation of gas hydrate, stress sensitivity, numerical simulation

摘要：

基于应力敏感性实验得到了储层渗透率、孔隙度和弹性模量等物性参数随有效应力的变化规律，结合现有水合物藏物性参数与水合物饱和度的关系模型，建立了水合物藏物性参数的综合动态模型。该模型全面考虑了水合物分解效应以及储层应力状态变化对物性参数的影响。水合物藏降压开采实例研究表明，水合物分解效应和储层应力敏感性是影响储层物性参数的两个重要因素。其中水合物分解效应起主要控制作用，造成水合物分解区储层渗透率和有效孔隙度明显增加，而弹性模量则明显降低；储层应力敏感性的影响覆盖整个压力波及区，其对物性参数的影响趋势与分解效应相反，因此对分解效应的影响具有一定抑制作用。

关键词: 天然气水合物藏, 物性参数, 水合物分解, 应力敏感性, 数值模拟