射孔水压裂缝在层状页岩的扩展机制

Propagation mechanism of hydraulic fracture of perforation in laminated slate

为明确射孔水压裂缝遇页岩层理面的扩展机制,基于弹性力学和断裂力学相关理论,建立射孔水压裂缝在层状页岩扩展的应力分析模型,并对裂缝偏转角、偏转裂缝在页岩和层理面扩展的临界水压进行分析,进而结合数值模拟,研究偏转裂缝遇页岩层理面的扩展机制的影响因素。结果表明:偏转裂缝遇页岩层理面的扩展机制主要取决于水平主应力差、射孔角度、层理面角度、页岩力学性质及层理面黏聚力等因素;若最大水平主应力方向与层理面夹角不大,偏转裂缝随水平主应力差的增大,由直接穿过层理面逐渐转化为沿层理面扩展;随着射孔角度、层理面角度和层理面黏聚力的增大,偏转裂缝的扩展模式则会发生相反变化;射孔段与层理面夹角越接近90°,偏转裂缝同时穿过层理面和沿层理面扩展的倾向性越大,越易形成网状裂缝。

On the basis of the elasticity and fracture mechanics,the propagation mechanism of hydraulic fracture of perforation intersecting with shale bedding plane was studied.The stress analysis model of hydraulic turning fracture in laminated slate was built and the deflecting angle,critical internal pressure of deflecting fracture in shale and bedding plane were analyzed.Then the factors of deflecting fracture intersecting with shale bedding plane were studied combined with numerical simulation.The results show that propagation mechanism of deflecting fracture depends on principal stress difference,perforation angle,bedding plane angle,mechanical properties of shale and cohesion of bedding plane.If the angle between the maximum horizontal principal stress and bedding plane is not large,with the increasing of principal stress difference,the propagation mode of deflecting fracture changes gradually from crossing the bedding plane to extending along the bedding plane.However,the change of propagation mode is opposite with the increasing of perforation angle,angle and cohesion of bedding plane.The closer to 90°of the angle between perforation and bedding plane,the higher tendency of crossing the bedding plane and extending along the bedding plane simultaneously and the map cracking is easier to form.