Simulation Analysis of Nonlinear Friction of Rod String in Sucker Rod Pumping System

Abstract

The nonlinear friction of rod string is an important foundation of dynamic simulation and efficiency optimization in sucker rod pumping system (SRPS). As we know, there are geometrical nonlinearity and contact nonlinearity of rod string in special oil well. Considering the earlier practical problems, a novel computational method of nonlinear friction of rod string is given. First, the simulation model of nonlinear friction is built. In the detail, the nonlinear friction of sucker rod string is made up of four parts: the viscous damping friction of rod surface, the viscous damping friction of rod coupling, liquid friction of centralizer, and the nonlinear Coulomb friction between rod and tube. Second, considering the rheology property of multiphase fluid in annular space, a simulation method of fluid pressure is proposed with software ansys. Based on earlier models, a numerical simulation model of nonlinear friction of rod string is built with visualbasic 6.0. Comparing experiment results with simulated results, good agreement is found, which shows the simulation model is feasible. The characteristics of fluid pressure and pressure gradient are analyzed. The instantaneous friction of rod string is simulated, and the sensitive factors of rod friction are analyzed. The novel simulation method solves the problem of environmental load calculation of large deformation rod. The analysis results have an important significance to guidance of optimization and design of SRPS.