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基于断裂力学理论,分别研究水压诱发的拉伸与剪切破坏特征。在水压诱发拉伸破坏方面,建立考虑井筒影响的地应力与水压耦合下的射孔尖端裂缝应力强度因子计算方程,推演该条件下拉剪复合应力状态下的断裂准则以及临界水压和启裂角的计算式。运用该方法从理论上分析了井筒周围存在对称的2条裂纹时,启裂水压和角度受射孔倾角、射孔长度、井筒半径及主应力差的影响。研究结果表明,依据推演的拉剪复合型断裂准则计算得到的射孔启裂水压和角度与试验结果吻合良好。参数分析表明:随着射孔长度或井筒半径的增加,临界水压减小。在水压诱发剪切破坏方面,则根据裂纹面的应力状态,分别推导裂纹处于压剪闭合状态和压剪不闭合状态下,水压诱发剪切破坏的断裂准则,并考虑非奇异应力对剪切断裂的影响,进一步推导压剪闭合应力状态下发生剪切破坏的临界水压计算公式。
Based on the fracture mechanics theory, the hydraulic-induced tensile and shear failure characteristics are studied respectively. In the aspect of water pressure induced tensile failure, the calculation equation of stress intensity factor of perforation tip crack under the coupling of ground stress and water pressure is established, and the fracture criterion under the condition of composite shear stress and the critical pressure Crack angle of the formula. This method is used to theoretically analyze the influence of cracking pressure and angle on the angle of perforation, perforation length, wellbore radius and main stress difference when there are two symmetrical cracks around the wellbore. The results show that the calculated fracturing pressure and angle of perforation coincide well with the experimental results based on the deduced tensile and shear composite fracture criterion. Parametric analysis shows that the critical pressure decreases with the increase of perforation length or wellbore radius. According to the stress state of the crack surface, the fracture criterion of the crack induced by hydraulic pressure is deduced respectively under the conditions of pressure-shear closure and pressure-shear failure, and the non-singular stress on the shear Cut the impact of the fracture, and further deduce the critical pressure of shear stress in the state of shear stress of the critical hydraulic formula.