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以南华北盆地户部寨第三系沙河阶组粉砂岩低渗透储层为例,总结了其中发育的5种类型构造裂缝组合,即:①南北向雁形张节理组成的共轭剪节理带;②东西向雁形张节理组成的共轭剪节理带;③缠结状多组剪切构造裂缝;④组合状交切的多组剪切构造裂缝及张裂缝;⑤散状无序排列的构造裂缝。在此基础上,建立光弹性试验构造物理模型,沿现应力场96°方向,均匀地对该模型逐步增加外载力。结果表明,沿各组合裂缝尖端分别形成对称于裂缝走向、且主轴垂直于裂缝的Ⅰ型等色线条纹;对称于裂缝走向、且主轴平行于裂缝走向的Ⅱ型条纹和斜交于裂缝走向的复合型(Ⅲ型)条纹。第①类组合裂缝尖端以Ⅰ型等色线条纹的拉张应力和张剪应力为主;第②类组合裂缝尖端以复合型(Ⅲ型)等色线条纹的挤压应力为主;第③、④和⑤类组合裂缝尖端的应力分布较为复杂。当模型外载荷接近1000kg时,裂缝尖端起裂,并开始发育显微裂缝,而当外载荷达1100-1200 kg时,沿裂缝尖端部位形成宏观裂缝,并开始扩展。5种类型的裂缝组合扩展发育程度由强至弱依次为:①,③,⑤,②,④。其中第①类共轭裂缝组合起裂最早,扩展最快,裂缝间的连通趋势最好,说明规则分布的构造裂缝组合,在垂直于外施加载衙时更易达到连通的目的。
Taking the low-permeability reservoirs of the Shahejie Formation of the Third Member of the Hubuzhai Formation in the South Huabei Basin as an example, five types of structural fractures are developed, namely: (1) Conjugate shear belts composed of geosynthetics ; (2) Conjugate shear zone consisting of east-west geogrid joints; (3) intertwined multiple sets of shear structural fractures; (4) combinatorial shear sets of multiple sets of shear structural fractures and fractures; (5) disordered Construct cracks. On this basis, the physical model of photoelastic test is established, and the external load force is gradually increased towards the model along the current stress field of 96 °. The results show that the type I isochronous stripe symmetrical to the fracture direction and perpendicular to the fracture is formed along each fracture tip. The type II stripe symmetrical to the fracture direction and the principal axis parallel to the fracture direction is oblique to the crack strike Compound (type Ⅲ) stripes. The tensile stress and tensile stress of type ¢ ò fracture tip are mainly Ⅰ type isochromatic line stripes. The fracture pressure of the fracture tip of type ¢ ò is dominated by the color stripe of compound type (Ⅲ) , ④ and ⑤ type of crack tip stress distribution is more complicated. When the load outside the model is close to 1000kg, the crack tip starts to crack and microscopic cracks develop. When the external load reaches 1100-1200 kg, macroscopic cracks are formed along the crack tip and begin to expand. The five types of fracture combinations extend the degree of development from strong to weak as follows: ①, ③, ⑤, ②, ④. Among them, the first type of conjugate crack combination initiated the earliest, the fastest expansion, the best trend of connectivity between the fractures, indicating the regular distribution of structural crack combinations perpendicular to the external application of loading Ya easier to achieve the purpose of connectivity.