Latest Technological Advances in Rod Pumping Allow Achieving Efficiencies Higher Than With ESP Systems

摘要

Two of the most important artificial-lift methods applied in oil wells are sucker-rod pumping (SRP) and electrical submersible pumping (ESP, with thousands of installations all over the world. Their operational features and application ranges are quite different, but in many cases either of them can be used in a given well. The final selection of the proper method has to be on the basis of energy efficiency, and the one requiring the least amount of surface power input is selected. This paper provides the necessary background for evaluating the effectiveness of the two lift methods investigated and for pinpointing the requirements of achieving maximum power efficiency of artificial lifting. The power flow in the pumping system is investigated, and the sources of power losses, along with their usual ranges, are described. The overall power efficiency of the system is defined by a simple formula that provides the necessary insight into the main components of the power losses occurring in different system elements. A thorough investigation of the efficiency components allows one to find the factors that most markedly influence the total system's power requirement. As shown in the paper, the most important requirement for achieving maximum effectiveness is the proper choice of the pumping mode (i.e., the combination of plunger size, stroke length, and pumping speed). The calculation of energy losses in the components of the ESP system is detailed, and the relative importance of the individual losses is shown. Because the components of the ESP system are connected in series, a relatively simple formula can be used to describe the effect of electrical and hydraulic losses on the efficiency of the total system. The terms of the final formula were investigated for their importance and contribution to the overall effectiveness of the ESP system. Results of this investigation provide crucial information that explain how to design an ESP system that provides the highest power efficiency. The practical use of the proposed calculation models is illustrated by presenting an example case where a relatively high liquid rate (1,300 B/D) from the same well is produced by rod pumping and by ESP. Detailed installation designs resulted in several different operation modes for both SRP and ESP. The paper demonstrates that using the latest technologies (e.g., high-strength sucker-rod connections), SRP can compete successfully with ESP installations by attaining higher energy efficiencies.