Research and Application of Rod/Tubing Wearing Prediction and Anti-Wear Method in Sucker Rod Pumping Wells

With the development of many kinds of oilfields, deep well, high deviated well and cluster well are increasing rapidly. Sucker rod pumping still remains a major artificial lift method. There are such problems as severe rod/tubing wearing and shortened rod/tubing life in high deviated rod-pumped wells, and the mechanism and prevention of rod/tubing wearing have not been understood properly. In order to understand the mechanism of rod/tubing wearing, a lateral load calculation model of rod/tubing is solved in this paper. The calculation results show that both the magnitude and direction of lateral force change dynamically with time and space in one stroke cycle. To better describe the rod/tubing wearing phenomenon, the lateral load is divided into two parts: the primary normal vector related to wellbore trajectory and axial force, and the secondary normal vector only related to wellbore trajectory and invariant with time. The three-dimensional and dynamic nature of lateral force can account for the rod/tubing wearing partially. The results of mathematical model show that the magnitude of lateral force at the same depth may differ greatly at different times, and its direction may also change periodically. It is likely to be bidirectional rod/tubing wearing when the primary normal force direction changes periodically. Simulation results show that the direction of lateral force is very likely to change periodically below the neutral point of rod string. This finding has accounted for the common double-faced and multi-faced rod/tubing wearing on the lower rod string. The periodic change of lateral force direction will cause rod/tubing collision, which is also an important cause for the rod/tubing wear below the neutral point. It is assumed qualitatively that the production parameters such as pump depth, stroke, stroke frequency and pump diameter are the major factors of the rod/tubing wearing according to field experience. In this paper, mathematic model is used to analyze the impact of these parameters on lateral force and the quantitative analysis is also conducted which provide theoretical foundation for the design of anti-wear production parameters. The mathematic model and method proposed in this paper are favorable to better accounting for the important phenomenon of rod/tubing wearing in rod-pumped deviated wells. They are capable of the quantitative calculation of lateral forces under different parameter conditions and the anti-wear design. This model has been applied to hundreds of highly deviated wells at Jidong Oilfield, prolonging rod/tubing life 58 days in average.