Evaluation of Linear Drives as an alternative Method for driving the Sucker-Rod String
Research output: Research › Master's Thesis
Linear pumping devices were mainly developed to improve the performance of the pumping system and also to overcome problems that generally arise during conventional beam pumping operations. The vertical construction without using heavy rotating counterweights eliminates excessive torque ratings. Downhole pump problems such as improper pump fillage, gaslocking and premature failure due to fluid pounding and excessive friction caused by high operating speeds are also highly decreased by the use of linear drives. This Master Thesis summarizes already existing linear devices such as the mechanical long-stroke pumping unit Rotaflex, the hydraulic long-stroke pumping unit DynaPump and the rack and pinion driven Linear Rod Pump (LRP). Therefore, their construction and operation is discussed in detail, followed by a precise analysis of the kinematic behaviour. Furthermore, safety aspects, special features, limitations and advantages compared to conventional beam pumping units are taken together to facilitate their selection for artificial lift applications. Afterwards, the applicability of ball and planetary screw drives as a new technology and a new alternative for driving the sucker-rod string is examined. As Bosch Rexroth is one of the market leaders regarding drive and control technologies, the design and product selection is based on their product line. At first, an electromechanical cylinder, using either a ball or planetary screw assembly, was designed to be vertically installed without the use of counterweights, whereas the construction design was optimized by using a 2:1 pulley system, like it is used for DynaPump units. This highly increases the capacities and makes it possible to theoretically compete with already existing vertical pumping devices. The specially designed electromechanical cylinder was calculated for an example case to point out threshold values of the construction. Furthermore, ball and planetary screw assemblies with increased stroke lengths were examined properly to verify their applicability as an artificial lift system. It was found that the use of a counterweight system would be necessary. Additionally, a distinction between two different options, the driven screw and the driven nut system, had to be made, whereas the driven nut system was proven to not have the capability of carrying increased rod string loads. The driven screw system was successfully calculated for two different stroke lengths. When calculating the example cases, the objective was also to point out threshold values of the construction. The last part includes a summary and comparison of all linear devices.