Buckling Prevention Using the Tensioning Device

摘要

A large fraction of artificially produced oil from mature, almost depleted reservoirs is lifted with sucker rod pumps. To increase the oil recovery factor under profitable conditions the objective is to reduce the operational costs, consequently decreasing the required number of maintenances and interventions. An essential cause of failures within rod pumps is buckling of the sucker rod string which occurs if the compressive load in individual rods exceeds a critical value. It causes a reduction of the volumetric efficiency and an increase of erosion and corrosion. The meantime between failures (MTBF) is relatively low and expensive changes of the rod string are required. This paper presents an approach to prevent buckling by tensioning the rod string during the whole pumping cycle with the tensioning device, which is integrated in the rod string below the pump plunger. In addition, an optimization of the tapered rod string is performed to reduce the mass of the reciprocating rod string. The system analysis is performed by a simulation of the downhole installation, which is verified by numerous dynamometer measurements, from the surface and downhole, of different operating oil wells. The result of the simulation is the distribution of the tension in the sucker rod string from the polished rod to the pump plunger. With this knowledge, a rod string with optimum usage of material strength and crosssections is designed. The tensioning device was already tested in a sucker rod pumped oil well in Austria. The result was a saving of electrical energy costs for the driving unit, and reduced number of workover operations. The tensioning device is simple but efficient and can be used within each sucker rod pump application. It prevents the system from buckling with a minimum amount of investment.