致密砂岩油气储层岩石变形理论与应力敏感性

在致密砂岩油气藏开发过程中,由于孔隙压力下降,导致有效应力增加,储层岩石孔隙、裂缝发生形变和渗透率受到影响。从岩石力学角度分析了与致密砂岩形变相关的理论及形变影响因素,并通过应力敏感性实验研究了有效应力改变条件下的致密砂岩岩样孔隙度、渗透率变化规律。结果表明:致密砂岩形变主要为应力变化时孔隙体积及裂缝宽度的变化,认为致密砂岩油气藏开发过程中储层岩石的形变一般属于弹性形变或者弹-塑性形变。形变取决于岩石碎屑颗粒硬度、颗粒之间接触关系、胶结情况、岩石中裂缝发育特征等。有效应力增加在压缩致密砂岩孔隙、喉道体积以及裂缝宽度的同时,也使得其渗透率大幅度降低,造成严重的储层损害。

DEFORMATION THEORY AND STRESS SENSITIVITY OF TIGHT SANDSTONES RESERVIORS

During exploiting the tight sandstone oil and gas reservoirs, the descent of pore pressure will induce the virtual stress increase, which makes the formation rocks deformation and the porosity permeability descent. The theories and the deformation reasons about the tight sandstone are analysed from rock mechanics point of view in this article. With the virtual stress alteration, the tight sandstone samples porosity and permeability change rule has been studied by the stress sensitivity experiment. The result shows that the porosity volume and the fracture width change are the main issues of the tight sandstone deformation, the deformation types in tight sandstone oil and gas reservoirs are mainly about elastic deformation and elastic-plastic deformation. The interior factors of tight sandstone result in tight sandstone deformation, such as grain's rigidity, contact and cementation relationship between grains, the characters of fracture in tight sandstone, and so on. With the virtual stress increase, the tight sandstone porosity volume and the width of the fracture are compressed, the permeability of the tight sandstone decrease in much extent, which will lead to a serous formation damage.