多级循环泵注水力压裂模拟实验研究

超深储层地层起裂压力较高，水力压裂受现场泵注设备的限制严重，文中重点研究了大尺度水力压裂物模实验水泥样品尺寸（762 mm×762 mm×914 mm）在循环和常规两种泵注条件下的起裂扩展和声发射规律。实验结果显示，（1）相对于普通泵注，采用循环泵注方式进行水力压裂可以有效降低起裂压力，类似于单轴和三轴循环加载岩石力学行为，都是由于循环加载引起疲劳损伤；（2）对于螺旋射孔完井方式，水力压裂裂缝只从最薄弱射孔处起裂，一旦起裂后其他射孔孔眼很难再开启，水力压裂现场应合理选择分段距离和簇间距，实现储层改造效率最优化；（3）循环泵注水力压裂存在Kaiser效应（当加载应力到前次加载最高应力值时出现的声发射信息）。因孔隙流体扩散到岩石并导致孔隙压力的局部上升，破坏模式仍然可以由摩尔圆表示。研究成果对循环泵注条件的裂缝扩展规律研究以及发展新型压裂改造技术具有重要意义。

Experimental study of hydraulic fracturing simulation for multistage circulating pump injection

For ultra-deep reservoir, the higher formation temperature and fracturing pressures lead to the limitation of pumping equipment in hydraulic fracturing. The paper focuses on the breakdown pressure and acoustic emission(AE) monitoring in large-scale hydraulic fracturing laboratory experiment with 762 mm×762 mm×914 mm in cement sample size by cycle and general injection. The test results show that: (1) Initiation pressures can be reduced on cyclic injection relative to general injection. Cyclic injection can bring about fatigue, which like the behavior of rock under uniaxial and triaxial cyclic loading. (2) For spiral perforation completion wellbore, the hydraulic fracture initiation only starts from the weakest perforation. Once the fracture is initiated, the other perforation holes are hard to reopen. The fracturing distance and cluster spacing should be chosen reasonably in hydraulic fracturing, to optimize the efficiency of reservoir stimulation. (3) The occurrence of the Kaiser effect before fracture initiation is the result of pore fluid diffuse to rock and cause the local rise in pore pressure, the failure modes can still be represented by Mohr circle. The results of the law of fracture propagation in cyclic injection, which is of great significance for the development of new fracturing technology.