应用DIC研究裂隙分布对层状复合岩力学特性及变形破坏影响

Influence of fissure distribution on mechanical properties and deformation failure of layered composite rock based on DIC

在储层压裂改造时,裂纹常在两种及以上的复合岩体中扩展,因复合岩岩性不同,会影响到压裂裂纹的走向和扩展。该文通过对含不同裂隙倾角和位置的复合试样进行单轴压缩试验,探究裂隙分布对复合岩体的力学特性、裂纹扩展及破坏的影响规律。主要结论如下:1)复合完整岩强度主要取决于强度较低的砂岩。2)裂隙分布对岩样力学性质的影响:3种裂隙位置的试样峰值强度随裂隙倾角增加而增加;在相同角度下,裂隙位于砂岩部分(FS)时劣化作用最强,裂隙位于大理岩部分(FL)时劣化作用最弱;裂隙分布对岩样破坏的影响:复合裂隙试样的裂隙位于砂岩时,试样的破坏主要为张拉破坏;裂隙位于交界面和大理岩时,砂岩部分随角度变化由拉伸破坏转变为剪切破坏,表现为“Y”形的破坏模式;裂隙倾角较小更易产生张拉裂纹,倾角较大更易产生剪切裂纹。3)复合裂隙样的裂隙倾角为0°~60°时,首先在裂隙尖端产生高应变区,随着加载的进行演变为应变局部化带,应变局部化带优先向较软的砂岩部分扩展。

During reservoir fracturing,cracks often propagate in two or more types of composite rock mass.Because of the different lithology of composite rock,the strike and propagation of fracture cracks will be affected.The main conclusions are as follows:1)The strength of composite intact rock is mainly dependent on the lower strength sandstone.2)Influence of fissure distribution on mechanical properties of rock samples:The peak strength of samples at three kinds of fissure locations increases with the increase of fissure angle.At the same angle,the deterioration is strongest when fissures are located in sandstone(FS),and weakest when fissures are located in marble(FL).Influence of fissure distribution on rock sample failure:When the fissure of the composite fissure specimen is located in sandstone,the failure of the specimen is mainly tensile failure;when the fissure is located at the interface and marble,the sandstone part changes from tensile failure to shear failure with angle change,showing a"Y"shaped failure mode.Smaller dip angle of fissure is more likely to produce tensile crack,larger dip angle is more likely to produce shear crack.3)The strain localization zone is formed gradually in the failure process of the composite intact sample,and the location of the localization zone is usually the location of the crack.When the angle of the composite fissure sample is 0°-60°,a high-strain zone is generated at the fracture tip first,which evolves into a strain localization zone with the loading process,and the strain localization zone first expands to the softer sandstone part.