为研究层状复合岩石的力学损伤特性,以深部致密储层砂岩及泥岩为研究对象,通过相似材料模型试验制备层状复合类岩石,开展单轴压缩试验并辅以声发射系统及数字图像修正(DIC)系统全过程监测,得到层状复合岩石的强度及弹性模量等物理力学参数。研究声发射振铃计数与岩石损伤演化过程对应规律,将单轴压缩下层状复合岩石损伤过程划分为初始损伤、损伤稳定发展及损伤加速三个阶段。以声发射内部损伤演化特征及DIC表面损伤演化特性为基础,建立了基于双损伤因子表征的层状复合岩石损伤本构模型。结果表明:3类岩石中,A类岩石的强度及弹性模量分别高于B类岩石21%和24%,AB类层状复合岩石的强度及弹性模量则低于B类岩石3%和4%。A类岩石以拉伸破坏为主,B类岩石多呈单斜面剪切破坏,AB类复合岩石主要沿胶结层理面或强度较弱部分产生拉伸-剪切滑移型破坏。三类岩石加载初期声发射活动较弱,在峰值应力时信号值达到最大。文中提出的模型合理地揭示了单轴压缩下层状复合岩石内部结构发展与外部裂纹萌发、扩展与贯通的损伤演化机理。

To study the mechanical damage characteristics of layered composite rocks, sandstones and mudstones from deep tight reservoirs were selected as research objects. Layered composite class rocks were prepared by similar material model tests. Uniaxial compression tests were conducted and supplemented with Acoustic Emission (AE) and Digital Image Correlation (DIC) systems to obtain physical and mechanical parameters such as strength and elastic modulus of the layered composite rocks. The corresponding law of AE ring count and rock damage evolution was obtained. The damage process of layered composite rock under uniaxial compression was divided into three stages: initial damage, stable damage development, and damage acceleration. In line with the internal damage evolution characteristics of AE and the surface damage evolution of DIC, a damage constitutive model of layered composite rocks based on dual damage factor was established. The strength of sandstone-like rock (rock A) is higher than that of mudstone-like rock (rock B) by 21%, and elastic modulus by 24%; the strength of layered composite rock (AB) is slightly lower than that of rock B by 3%, and elastic modulus by 4%. Rock A is subjected to tensile failure, B to shear failure with single inclined plane, and AB to tensile-shear slip failure along cemented bedding plane or weak parts. The three types of rocks see weak AE in the initial load stage but strongest AE signals at peak stress. Analysis of strain cloud diagrams of the DIC system revealed that the deformation characteristics of the layered composite rock under uniaxial compression were mainly tensile-shear-slip damage. The present model reasonably revealed the damage evolution mechanism of internal structure development and external crack initiation, expansion, and penetration of layered composite rocks under uniaxial compression.