Operating Experience With The Alpha I Pumping Unit: A New Alternative In Artificial Lift

Abstract

Abstract A case history on the performance of the Alpha I pumping unit is presented. The operational and mechanical problems which have been encountered are discussed and the solutions that were employed are related. It is shown the unit has numerous applications particularly in high volume wells which are usually outside the particularly in high volume wells which are usually outside the operating range of beam units. Numerous studies and tests which have been conducted on the unit reveal that the Alpha I is competitive with beam units and submergible pumps with respect to lifting costs and energy efficiency. Although the unit has experienced operating problems, it is concluded that with additional experience a portion of these problems and expenses can be eliminated. Introduction Since February, 1977, Cities Service Company has been operating an Alpha I pumping unit in the Prue Waterflood near Oklahoma City. This pumping unit was the first of its type to be employed by Cities Service in its field operation. Furthermore, the application of the Alpha I, at that time, had seen limited application elsewhere and, therefore, operating experience was minimal. As a result, its performance has been under continued observation and numerous tests have been conducted on the unit. This paper describes the results of these observations and tests. Particular emphasis is given to:general operating performance, Particular emphasis is given to:general operating performance,operating costs, andefficiency. This paper is also intended to present sufficient information so that the producer who has little or no experience with the Alpha I may gain a basic understanding of its applications, capabilities, limitations, and operating characteristics. UNIT DESCRIPTION AND OPERATION Although the Alpha I has been manufactured for over three years and literature on the unit is readily available, a brief description of the mechanics and operation should be beneficial. The unit is simply a system of cables, pulleys, and weights which operate basically as a "draw works" to raise and lower the rod string, Figure 1. The Alpha I operates at three strokes per minute with a stroke length of 40 feet. per minute with a stroke length of 40 feet. When first viewed, the most dominant feature is the appearance of three large diameter wheels. The outer wheels are simply idler pulleys which serve the same purpose as a horse's head in guiding the cable either into the well or the counter balance hole. The center wheel, which is called the power drum, is driven by a conventional pumping unit gear box, operated in turn by a standard oil field electric motor. The motor is operated alternately in both forward and reverse to impart an up and down motion to the rod string. The heart of the entire system is the power drum. This drum is strategically designed with spiraling cable grooves which cause the cable to follow paths that change the radius of the drum near the end of each portion of the stroke. This greatly alters the moment arm of the well-side and counter weight cables, Figure 2A. The effect of this action is — a, the top of the upstroke — to make the well load "heavy enough to stop its upward motion, then actually reverse the direction of rotation of the system. Conversely, at the bottom of the stroke, counter weight torque is rapidly increased to stop downward rod motion and again reverse the system momentum Figure 2B. Thus, the cam system causes the opposing weights to "coast" to a smooth stop and reverse direction at the top and bottom of each stroke. During this coasting period, the electric motor is actually switched off for a significant length of time (approximately 30%). The reversing of the power drum causes the gear box to spin the motor up to about two-thirds of its synchronous speed before it is switched on again. As a result, a sizeable savings in electrical costs can be realized. The counter balance system of the Alpha I is just another aspect which makes the unit a radical departure from the classic beam unit.