炭质页岩巴西劈裂载荷下破坏过程的时空特征研究

页岩在加载过程中的破裂时机及其空间位置研究对于页岩气探测及储层评价具有重要意义，为此开展了不同层理倾角条件下页岩的巴西圆盘劈裂载荷下的破坏过程试验，采用数字图像相关技术（DIC），全程跟踪页岩裂纹萌生、扩展和贯通全过程的变形场实时演化特征，同时记录力-位移曲线，利用扫描电镜获得炭质页岩的破裂面特征及微观结构，采用宏、细观相结合的手段，研究不同层理方向炭质页岩微裂缝起裂时间、空间位置和扩展规律及其破裂机制。结果表明：页岩的巴西劈裂强度随层理方向与加载方向角度的增大而逐渐增大；随加载方向与层理面夹角的增加，裂缝萌生的时间逐渐增加，而裂缝从萌生、扩展到贯通所用时间逐渐减少。所有角度试件基本从试件端部萌生裂缝并沿层理面扩展，除90°试件外，不同层理倾角试样主裂缝破裂的位置逐渐偏离中心位置而向试件外侧发展。各角度试件主破坏类型存在一定差异性，除90°试件竖向主裂缝为张拉破坏外，随加载方向与层理面夹角的增加，各加载角度试件的主破裂模式从张拉剪切破坏逐渐过渡为剪切滑移破坏。

Time-space laws of failure process of carbonaceous shale in Brazilian split test

It is great crucial for shale gas exploration and reservoir evaluation to investigate the rupture time and spatial position during the loading process of shale. Brazilian tests on shale were carried out under different angles between the loading direction and bedding planes to examine failure process. The digital image correlation (DIC) technique is adopted to track shale real-time deformation field evolution of crack initiation, propagation and coalescence during entire process, meanwhile, the force-displacement curve is recorded. Scanning electron microscopy (SEM) is applied to obtain fracture surface characteristics and microstructure of carbonaceous shale. Based on experimental data, the relationships between the loading direction and the micro fracture initiation time, spatial location, propagation rules and fracture mechanism of shale are explored. The results show that shale Brazilian disc split strength gradually increases with the increase of the angle between the loading direction and bedding plane. With the increase of the angle, the crack initiation time gradually increases, but the consumed time from crack initiation, propagation to damage decreases. The cracks basically produce from the ends of the specimen and propagate along the bedding plane. The cracks gradually develop from the middle of the specimen to the outside along with loading angle from 0° to 90° except the vertical main fracture of 90° sample. There exists a certain difference between main damage types of different shale specimen with loading directions. The fracture mode gradually transits from tension shear failure to shear sliding failure except the vertical main fracture of 90°sample with the increase of the angle between the loading direction and bedding plane.