Ⅰ型裂缝经层理岩石界面拐折扩展规律研究

Crack Propagation Law Research of Bedding rock Interface

依据非常规储层层状岩体的结构特点,根据相似原理制作不同材料、不同界面性质的层状岩体试件,通过三点弯曲试验发现裂缝经过异弹性材料界面后扩展转向,力学性能差异越大,界面强度越弱,裂缝转向角度越大。以试验参数为基础,建立了垂直裂缝扩展的平面应变模型,并获得了垂直裂缝经过砂/泥岩界面扩展过程中应力场,计算了裂缝尖端应力强度因子的变化规律,获得了裂缝偏转角度。通过计算发现:裂缝偏转是由界面的剪切应变增大而引起剪切应力强度因子增加,使得Ⅰ型裂缝经异弹界面而发展为Ⅰ—Ⅱ型复合裂缝引起的。

According to the structural feature of unconventional reservoir stratified rock mass, stratified rock mass speci- mens of different materials and interface properties are manufactured on the basis of similarity principle. Veer extension after cracks cross different elastic material interface is found through the three point bending experiment, the more difference be tween the mechanical properties, the weaker interracial strength, and the larger steering angle the crack has. Based on the experiment parameter, a plane strain model of vertical crack propagation is established, the stress field of vertical crack via sand/shale interface in the process of the extension is obtained, the stress intensity factor variation of crack tip is calculated, and the angle of crack deflection is gained. The results of calculations show that the veer extension is caused by that the I type crack turning to Ⅰ-Ⅱ type compound crack when the shear stress intensity factor increases because of the increasing interfacial shear strain.