Dynamic Response of Coiled Tubing Perforation Under Unstable Fluid Injection

Hydraulic jetting perforation and fracturing with coiled tubing (CT) has been widely applied in low-permeability reservoirs. In perforating operations, obvious oscillation of the CT between the spool and gooseneck often appears. This is mainly caused by the unstable fluid flow in the CT. This paper presents the analytical models for the stability of CT under unstable fluid injection. Lateral fluctuating force model of CT is proposed. The dynamic equations for lateral vibration of CT are established based on the structural dynamics theory. Moreover, the effects of rotation speed of fracturing pump, flow rate of fracturing pump, and length of CT on response displacement and natural frequency are discussed. The results indicate that under unstable fluid injection, the first-order and second-order response displacements for lateral vibration of CT present the fluctuation with increasing flow time. With increasing rotation speed and flow rate, the lateral vibration of CT becomes faster, and the resonance of CT is prone to occur. With increasing length of CT, the stability of CT becomes worse. In general, the unstable fluid flow in the CT caused by the unstable flow rate of fracturing pump has an influence on the stability of CT in perforating operations. Therefore, it is recommended to reasonably control the flow rate and rotation speed for fracturing pump in engineering applications.