Numerical Simulation on Water Hammer Pressure Generated by the Slippage of Bridge Plug During Fracturing

The bridge plug is an essential isolation device in multistage fracturing. It is significantly vital for the bridge plug to maintain complete isolation at the bottom hole. Judging the state of the bridge plug has a huge effect on the subsequent fracturing. In this paper, a simplified flow field model of bridge plug-wellbore-perforation at the bottom is established. The computational fluid dynamics (CFD) method is used to analyze the flow field characteristics near the bridge plug under different conditions, including the bridge plug slipping, the perforation opening and the bridge plug anchoring again after slippage. The results indicate that a water hammer pressure is generated when the flow area changes in the wellbore. The pressure variation includes initial pressure drop, pressure fluctuation and eventual pressure drop. For the condition of the bridge plug slipping, the initial pressure drop is the largest, and the pressure fluctuation is the lowest. When the flow rate increases from 1.6 m3/min to 3.2 m3/min, the initial pressure drop is improved from 1.0 MPa to 4.3 MPa. The pressure fluctuation is improved from 0.23 MPa to 1.0 MPa. The rate of change of pressure is approximately twice the rate of change of flow rate. The pressure fluctuation and eventual pressure drop are unobvious compared with the initial pressure drop when the perforation opens suddenly. In addition, an incredibly huge water hammer pressure is generated when the bridge plug anchors after slippage. It is inferred that Once the bridge plug slips, it is difficult to anchor again. The results of this paper are expected to provide a new method for monitoring the working condition of bridge plugs at the bottom hole.