一种新型多级分段压裂自动投球器

投球压裂是页岩气水平井分段压裂改造的常用技术,目前的投球器存在着压裂球尺寸小、投球数量有限、结构过于复杂、适用性差等问题,不能满足页岩气井大通径、小间距压裂作业的需求。为此,设计出了一种转板式大通径井口自动投球器,该投球器上端设置储球筒,下端的底座内部布置投球机构,通过驱动电机控制投球机构实现逐个投球的功能;采用FEM(有限单元法)对该投球器的投球过程进行碰撞分析,通过任意拉格朗日欧拉(ALE)网格自适应方法和耦合的光滑粒子流体动力学(FEM-SPH)方法进行仿真模拟和样机实验。研究结果表明:①投球碰撞在转板上边缘处产生最大的等效应力、等效塑性应变和位移,产生的最大应力在600 MPa左右,小于42CrMo的屈服强度930 MPa,满足强度要求,并且具有一定的安全余量;②样机成功实现了投球直径介于64～108 mm、投球级差为4 mm的12级分段压裂连续投球测试。结论认为,该投球器操作简单、适用性广,可有效满足页岩气水平井多级分段压裂工艺的需要。

A new type of automatic ball injector for multistage fracturing

Ball fracturing is a kind of technology that is commonly used for multistage fracturing of shale gas horizontal wells. At present, the ball injector cannot satisfy the operation demands of large bore and small spacing fracturing of shale gas wells due to its disadvantages, such as a small size of fracturing ball, a limited number of balls, complicated structure and poor applicability. In this paper, a new type of automatic ball injector with rotating plate and large bore was designed. There is a ball storage at the upper part of the ball injector and a ball injecting mechanism inside the pedestal at the lower part. And the ball injecting mechanism is controlled by the drive motor to inject the balls one by one. Then, collision analysis was carried out on its ball injecting process by using finite element method (FEM). Finally, simulation and prototype tests were conducted by using the arbitrary Lagrangian–Eulerian (ALE) mesh adaption method and the coupled smoothed particle hydrodynamics method (FEM–SPH). And the following research results were obtained. First, in the process of ball collision, the maximum equivalent stress, equivalent plastic strain and displacement are generated at the edge of the rotating plate. The maximum stress is about 600 MPa, which is less than the yield strength of 42CrMo (930 MPa), so the strength requirement is satisfied with a certain safety margin. Second, the prototype successfully passes the continuous ball injecting test of 12-stage fracturing process with the ball diameter of 64–108 mm and the ball contrast of 4 mm. In conclusion, this automatic ball injector with rotating plate and large bore is advantageous with simple operation and wide applicability and can effectively address the needs of multistage fracturing of shale gas horizontal wells.