射孔水平井分段压裂起裂压力理论研究

摘要

Based on the superposition and elasticity theory,a theoretical model of initiation pressure calculation in staged fracturing of perforated horizontal well was developed while considering the effect of wellbore pressure,formation stress distribution,and stress induced by hydraulic fracture. The change of initial and subsequent fractures initiation was studied. The results show that the stress induced by initial fracture is influenced by fracture spacing. When the initial fracture length is constant,the induced stress along wellbore decreases gradually until the stresses reach initial formation stresses. Fracture initiation of a perforated horizontal well is affected by perforation azimuth. The optimum azimuth is determined by the stress distribution around wellbore. Induced stress can increase subsequent fractures initiation pressure. The degree of impact is increasing with the increase of fracture length. When fracture length is constant,the increase amount of initiation pressure would drop rapidly with the increase of fracture spacing.%综合考虑井筒内压、原始地应力分布、先压水力裂缝的诱导应力等因素,根据叠加原理及弹性力学理论,建立了射孔水平井分段压裂起裂压力计算模型,分析了初始及后续裂缝的起裂规律.研究结果表明,初始裂缝产生的诱导应力分布受裂缝间距影响.当初始裂缝缝长一定时,沿井筒方向诱导应力逐步降低,直至地应力场趋于原始地应力场；射孔水平井裂缝起裂受射孔方位角的影响,最佳射孔方位由井筒周围地应力分布决定；先压裂缝产生的诱导应力场会导致后续裂缝的起裂压力增大,这种影响会随着裂缝半缝长的增大而增强;半缝长一定时,起裂压力的增加幅度随着裂缝间距的增加递减.