Paper: Sizing Pumping Unit Prime Movers

Due to the unusual nature of the loads encountered in oil well pumping service, a somewhat different approach is necessary for properly sizing pumping unit prime movers. This unusual load can sometimes be best explained by a look at the cycling torque loads imposed on a pumping unit gear reducer by the polished rod load. This can be illustrated by a dynamometer analysis of a typical well. A quick, yet reliable, method of determining horsepower requirements using only depth, pump size, SPM, and surface stroke length can be derived. When these methods are used in conjunction with knowledge of the unusual type loads encountered, an obvious advantage can be seen in selecting prime movers with operating characteristics suited to cycling loads. Utilization of heavy flywheel, single cylinder engines with the ability to deliver "instantaneous horsepower" considerably over the engine's continuous horsepower rating allows a more appropriate engine sizing for the "average" load. A similar approach can be taken in the selection of electric motors for pumping service through use of the characteristics found in the high slip design.