双向受压载荷具内压斜裂缝的起裂与扩展

基于力的平衡原理及断裂力学理论，针对射孔方位与最大主应力方向不重合的情况，建立了裂缝模型，推导了双向受压具内压斜裂纹的应力场，提出了裂纹开裂与延伸的最大应力强度准则。根据现场实际情况，应用有限元法对水力压裂初裂缝的应力强度场进行了计算，分析表明，该准则具有很高的精度。通过模型计算可以看出，当射孔方位与主应力方位不匹配时，初裂缝将转向，形成一条曲折的裂缝，给水力压裂施工带来很多困难；应用定方位射孔技术可以有效地解决该问题。

INITIATION AND PROPAGATION OF SLANT FRACTURE WITH INNER PRESSURE AND BIAXIAL COMPRESSIVE PRESSURE

Based on the force balance principle and fracture mechanics theory, regarding with the misalignment between the perforation azimuth and the azimuth of the maximum principle stress, this study developed the fracture model, then derived the stress field of slant fracture with inner pressure and biaxial compressive pressure, and established the maximum stress intensity criteria of fracture initiation and propagation. The stress intensity field of initial hydraulic fracture was calculated by finite element method according to field data. The calculating results prove that the criteria are precise. From the calculation by the model, it showed that a tortuous fracture would be induced while the azimuth of the perforation doesn't match the azimuth of principle stress, which will bring many difficulties for hydraulic fracturing operations and sometimes results in operation failure. However, if the oriented perforation technology was adopted this problem can be solved effectively.