致密砂岩孔隙尺度应力敏感分析

油田开发过程中,有效应力随地层压力减小而增加,储层岩石发生形变,孔隙度及渗透率降低,应力敏感现象明显。基于应力敏感实验以及岩心CT扫描图像,采用MIMICS和ANSYS软件,利用有限元方法从孔隙尺度对致密砂岩岩心单轴受力及三轴受力过程进行模拟,分析了应力条件下孔隙结构的变化规律。结果表明:非均质性对储层应力敏感具有明显影响;单轴应力作用下,岩心孔隙边缘和孔隙连接处存在应力集中现象;节点位移呈层状分布且受应力传递的影响;三轴应力作用下,岩心骨架受力变形,孔隙概率分布左移,导致平均孔径、孔隙度及渗透率损失。孔隙度越高,其平均孔径降低幅度越大,即孔隙度降低幅度越大。

Pore-scale stress sensitivity analysis of tight sandstone

During the oil and gas developing process, the effective stress increases with the decreasing formation pressure, leading deformation in reservoir rock, which causes loss in both porosity and permeability. In this work, based on the stress sensitivity experiments and the core CT scanning image, with the MIMICS and ANSYS softwares, the finite element method was adopted to simulate the single axial stress and triaxial stress exerting on cores. Analysis of the deformation law of the pore structure under the stress condition was made on pore scale based on simulation result. The results show that the heterogeneity has obvious influence on the stress sensitivity of reservoir, and there is stress concentration at the pore edge and the conjunction of cores under uniaxial stress, the displacement of the nodes is affected by stress transfer and distribute in layers. Under triaxial stress, the core skeleton is deformed and the distribution of pore moves along the left direction, leading a decrease in both porosity and permeability. And the higher the porosity is, the greater the decrease of the average pore diameter, namely the greater reduction extent of porosity.