Field Testing A Front-Mounted Mechanical Oilfield Pumping Unit

Publication Rights Reserved Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and considered for publication in one of the two SPE magazines with the paper. Several major oil companies have made recent, head-to-head studies comparing the mechanical properties of a front-mounted, non-symmetrical mechanical pumping unit to those of its well known conventional counterpart. The results of there tests have shown that in many applications, the lower torsional and structural loading of the front-mounted unit allows the operator to use smaller and less expensive equipment to handle the same fluid loads. This paper includes one of these recent, representative, oil company studies and its conclusions. During the latter part of 1956, a front-mounted, non-symmetrical, mechanical beam-type pumping unit was developed for general oilfield service. This machine was designed for the same wide range of application covered by the standard or conventional surface pumping unit. Although this new pumping system employed the same general structural components, its mechanical characteristics, and hence, its functional ability, were substantially different from those of the conventional unit. The difference in the mechanical properties of the new machine was produced by a re-arrangement of the components of the conventional unit. This changed it from a symmetrical Class I lever system [fulcrum at mid-beam] to a non-symmetrical Class III lever system [fulcrum at rear beam]. The well load and counterbalance torque were dephased by providing an angular off-set in the crank, and moving the gearbox away from the well a proportionate amount, while driving the machine in a particular direction of rotation. This front-mounted [Class III lever] unit [Fig. 1] combines the simplicity, ruggedness, and high efficiency of the conventional unit, with the beneficial rod motion and ease of counter-balance of the air balanced system, and provides, in addition, a relatively uniform torque demand on both primer mover and gear reducer. This new Class III geometry makes possible several desirable pumping unit properties:A simple means of presenting the normal rod load variation of each pump stroke as a relatively uniform torsional load to both gear reducer and prime mover. By smoothing out these peak torsional loads it is often possible to use a smaller gear reducer and prime mover to handle a given application.A method of lifting rods and fluid with lover upstroke acceleration so that in many cases the peak polished rod load is appreciably reduced. This property not only tends to minimize rod loading but it also tends to minimize production losses because of reduced rod maintenance.