LAUSR

In pump-starting and pump-stopping, because of the rapid change in fracturing fluid, the piping is subjected to water hammer effect. Water hammer effect results in severe vibration, which may damage the pipe or cause sealing failure of connections. To quantitatively analyze the water hammer effect and vibration characteristics in pump-starting and pump-stopping, the characterized lines method was adopted to analyze the velocities and dynamic pressures of fracturing fluid, as well as the axial velocities and additional stresses of piping at different depths. It shows that in pump-starting, the velocities and dynamic pressures of fracturing fluid as well as the axial velocities and additional stresses of piping increase greatly with increased flow rate of fracturing fluid. Meanwhile, the fluctuations of dynamic pressure and the axial velocities of piping decrease with increased depth. In the pump-stopping process, the shorter the pumping-stop time is, the higher the dynamic pressure of the fracturing fluid and the greater the axial velocity of the pipe. It is easier to damage the pipe in pump-stopping compared to pump-starting. The study provides a guidance of the flow rate of fracturing fluid, pump-starting time, and pump-stopping time to ensure safe fracturing.