Transverse vibration simulation of sucker rod string under normally distributed load caused by viscoelastic fluid in a curved wellbore

Abstract

The sucker rod string is eccentric due to the effect of wellbore bending. When the sucker rod string undergoes an eccentric motion within the wellbore containing viscoelastic fluid in the polymer flooding pumping wells, it is subjected to an alternating normally distributed load caused by viscoelastic fluid (NDLVF). In this paper, it is pointed out that the alternating NDLVF acting on the sucker rod string is the excitation of the transverse vibration of the sucker rod string. Moreover, the coupling relationship between the NDLVF and the transverse vibration displacement of the sucker rod string is considered. Based on the elastic vibration theory, the mechanical and mathematical model of the transverse vibration of a sucker rod string under the NDLVF in the curved wellbore is established. Then, the Runge-Kutta method is used to solve the simulation model, and parameter sensitivity analysis is carried out. The simulation results show that: (1) the NDLVF can significantly affect the transverse displacement of the sucker rod string and the rod-tubing contact force, which is an essential excitation for the transverse vibration of the sucker rod string in the polymer flooding pumping wells. (2) Due to the NDLVF presence, the contact collision between the rod string and tubing string occurs more frequently, and the rod-tubing contact force is increased. (3) The NDLVF effect on the transverse vibration of the sucker rod string is most noticeable near the neutral point of the sucker rod string. (4) With an increase in the polymer concentration, stroke length, and stroke frequency, the transverse vibration of the rod string becomes stronger. The transverse vibration simulation model of the sucker rod string under NDLVF in a curved wellbore plays a guiding role when analyzing rod-tubing eccentric wear and optimal allocation of a centralizer in the polymer flooding pumping wells.