Abstract:

Considering the effects of gas hydrate dissociation and the interaction between porous fluid flow and rock deformation, a gas-water two-phase non-isothermal fluid-solid coupling mathematical model was established for gas hydrate reservoirs, and a corresponding finite element program was developed. Taking a gas hydrate reservoir of Mexico Gulf as an example, the distribution and variation of the stress state and the physical parameters were analyzed. The results show that the effect of gas hydrate dissociation, fluid-solid coupling and borehole effect are the three major influential factors with different mechanisms, influence degrees and influence areas. The effect of dissociation is the main controlling factor and obviously causes the increases of effective porosity and permeability and the decreases of the elastic modulus and cohesion force. The fluid-solid coupling effect has obvious inhibiting effect on the varying trends of the physical and mechanical parameters caused by the effect of hydrate dissociation. More attention should be paid to the fluid-solid coupling effect.

Key words: gas hydrate reservoirs, depressurized production, physical parameters, fluid-solid coupling, mathematical model, finite element method

摘要：

将水合物分解效应融合到渗流场与岩土变形场的耦合作用中，建立了天然气水合物藏气、水两相非等温流固耦合数学模型，并开发了有限元程序。对墨西哥湾某水合物藏进行了实例研究,分析了储层应力状态、物性参数分布及动态变化规律。结果表明，水合物分解效应、流固耦合作用以及井眼效应是影响储层应力状态和物性参数的3个主要因素，其作用机理不同，影响程度和范围各异。其中，水合物分解效应是主要控制因素，会导致分解区储层有效孔隙度和渗透率显著升高，弹性模量和内聚力等力学性能大幅度降低；流固耦合作用对分解效应引起的物性及力学参数的变化趋势具有明显的抑制作用，同样不可忽视。

关键词: 天然气水合物藏, 降压开采, 物性参数, 流固耦合, 数学模型, 有限元法