A new type of automatic ball injector for multistage fracturing

Abstract

Ball-drop 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.