水力喷砂射孔孔道裂缝起裂机理研究

与传统射孔工艺相比，水力喷砂射孔方法产生的地层孔具有孔径大、孔道长和孔数少特点。针对射孔孔道影 响压裂裂缝形态问题，开展孔道周围应力分布及起裂机理的研究工作。研究中采用三维有限元数值模拟结合室内实 验验证的方法，分别从布孔方式、射孔方位和水平井筒方位方面，揭示了水平井近井筒区域喷砂射孔孔道产生的3 种 裂缝形态。研究表明，压裂裂缝倾向于从射孔孔道根部位置起裂；水平井筒与最小水平主应力夹角小于30°，两层布孔 可在近井筒区域产生一条横向裂缝，螺旋布孔和对称布孔产生多条横向裂缝；纵向裂缝比横向裂缝更易于产生，形成 纵向裂缝与横向裂缝相结合的扭曲裂缝；水平井筒与最小水平主应力夹角大于80°，产生一条纵向裂缝，与喷砂射孔参 数无关。该研究可为水平井水力喷砂射孔及压裂合理施工提供理论指导。

The Research on Fracture Initiation Mechanism for Sand Jetting#br# Perforation Technology

Compared with the shaped charge perforation，sand jetting perforations are characterized by bigger diameter，longer length and smaller perforation number. Because the fracture morphology will be affected by perforated tunnel，the stress distribution around tunnels and fracture initiation mechanism were studied for sand jetting perforation. Based on the 3D finite element computation method and the research results of indoor experiments，hole distribution，perforation azimuths and azimuths of horizontal well are evaluated to reveal three fracture shapes around wellbore. The results show that the fracture easily initiate from the root of perforation tunnels；when the degree of included angle θ between horizontal section and minimium horizontal stress is less than 30°，double layer perforation method can create one fracture，and multiple fractures are generated by helical perforation and symmetric perforation. Because longitudinal fracture is more easily created than transverse ones，hydraulic fracture process will lead to a contortion fissure. In the condition of θ more than 80°，there is only a longitudinal fracture in horizontal wellbore，which is not affected by perforation parameters. The result was also a theoretical basis for reasonable use of jetting perforation and hydraulic fracturing in horizontal well.