Key Technology Research Of Rod Pumped Well Sucker Rod Design Under Complicated Medium

With the oilfield entered the middle and later production periods, well fluid properties become complex gradually, then the broken rate of sucker rod has risen sharply, which leads to a higher production cost. It means that there exists inadaptability between the traditional design method of sucker rod pumping system and the production operation condition in middle and later production periods. It has an extremely vital significance that how to analysis the production operation condition of the sucker rod under complicated medium using the existing conditions, find out the key influence factor, modify sucker rod design method, and improve the fatigue life in order to increase the oil well production time efficiency.The composition and properties of oil-well produced fluid change in middle and later production periods, which have two aspects of effect. The one is the change of damping characteristics in wellbore, another is the change of vibration characteristics, including the sucker rod vibration and fluid column vibration. Based on this situation, the pipe flow characteristics and friction characteristic test schemes under complicated medium are designed, the pipe flow characteristics test, plunger-pump barrel friction characteristics test and polished rod-stuffing box friction test have been carried out with different rod-pipe combinations under aqueous medium and the polymer medium. According to the underground system damping coefficient calculation method, the damping coefficient variation curves under aqueous medium and the polymer medium are mapped provides the calculation basis for the design of sucker rod. Load characteristic of the rod-pumped well is studied, and liquid column mechanics model is established and solved by using finite difference method. The downhole pump outlet pressure simulation procedure is written, and the pressure test scheme is designed. Wellhead pressure and downhole pump outlet pressure tests are carried out, which verifies the correctness of the simulation program. Simulation program is used to calculate the outlet pressure of downhole pump under aqueous medium and the polymer medium with different conditions and their general rules are compared and obtained.The conventional sucker rod design method (SY) is analyzed, the maximum and minimum load calculation formulas are improved, and the solving method including damping is used to the vibration load. The calculation formula for the liquid column load part is modified by using the simulation result of the downhole pump outlet pressure and replacing the previous hydrostatic load, to consider the effect of liquid column vibration to the polished rod load, which makes the calculation more reasonable, it can achieve the design of new production wells and the optimization of existing wells under the middle and later production periods.