水平井分段压裂破裂压力计算

水平井分段压裂时，形成的初始裂缝会诱发井筒周围应力分布二次改变，产生诱导应力场。诱导应力场将会对后续裂缝起裂产生影响。在考虑原始井筒周围地应力分布状态的基础上，结合弹性力学理论和岩石拉伸破裂理论，建立了诱导应力场中井筒地应力分布模型和破裂压力计算模型。研究结果表明:诱导应力的大小和分布取决于裂缝间距、裂缝缝高及原始地应力。随着裂缝间距的增加，沿着井筒方向诱导应力逐渐变小；定间距时，随着裂缝高度的增加，破裂压力也随之增加；原始地应力分布与诱导应力场中破裂压力的变化规律无关，只决定着裂缝破裂压力增加的幅度。该结果对于优化水平井分段压裂设计具有一定的指导意义。

Breakdown pressure calculation of staged fracturing for horizontal wells

When a horizontal well is transversally fractured with multiple stages, initial crack can induce the secondary change of the wellbore stress, producing the induced stress ield which has an inluence on subsequent crack initiation. Based on the elasticity and tensile failure theory, this paper develops a stress distribution model around wellbore and a theoretical model for calculating the break- down pressure. The results show that size and distribution of induced stress depend on crack spacing, fracture height and in-situ stresses. The induced stress decreases along wellbore direction with the increase of crack spacing; when crack spacing is ixed, breakdown pres- sure increases as fracture height rises; in-situ stress distribution is independent with breakdown pressure change in induced stress ield, which only determines the increase amplitude of breakdown pressure. This result can be used to guide optimization design of staged fracturing for horizontal wells.