Prediction Of Sucker Rod String Dynamic Characteristics And Computer Simulation Research For Rod Pumping System

Rod pumping has a sizable proportion of mechanical oil production, the dynamic prediction of sucker rod string is a basic for system's efficiency analysis and optimal design. In this paper, the theoretical analysis and numerical calculation are deeply conducted for sucker rod string dynamic characteristics of rod pumping system. The main content is in the following:A kinematic model is developed for the mechanism of beam pumping unit, the displacement, velocity, acceleration in the hanging-point and the corresponding curves in a motion period are obtained. The dynamic analysis for the mechanism is given and the torque on the output shaft of the gear reducer is computed. The algorithm to obtain the position of crack counterbalance is put forward according to the criterion for the torque balance.The programming algorithm for simulating sucker rod string axis is introduced by using three order spline interpolation. Status of forces applied on the sucker rod string infinitesimal is analyzed and the wave equation describing the vibration of sucker rod string is established.A hybrid algorithm combining the implicit differential method applied in even mass sucker rod string with the variable step finite differential method applied in the boundary node of composite sucker rod string is proposed for solving the wave equation. By comparing the computed dynamometer card with that of actual measurements. It is found that the computing results are satisfactory. The influences on suspension point load and crackshaft torque are analyzed for different kinds of oil viscosity and material of sucker rod string.Taking account of motor rotating speed fluctuations, an equivalent mechanical model of rod pumping system is established. The motion differential equation of crankshaft and the wave equations of the sucker rod are solved simultaneously and the corresponding algorithm is proposed. The calculation result shows that the dynamometer card simulated by means of high-slip motor is clearly more approximate to the observed dynamometer card.The operation flow of software emulating the rod string dynamic characteristics of rod pumping system is introduced and the basic function of the software is also presented.