Effects of Speed Variation on the Performance and Longevity of Electric Submersible Pumps

Abstract

5%5 19349S ummary. The expanding usage of variable-speed drives (VSD'S) indicates that their effects, on electrical submersible pump (ESP) performance and longevity merit investigation. This paper demonstrates that speed variation makes ESP, equipment selection more complex and critical if maximum pump life is to be achieved. Thrust wear can dramatically affect pump longevity. A common conception is that the rates identifying acceptable thrust limits for any pump s,peed would be the at%nity-law projections' of the detining rates at 60 cycleslsec [60 Hz]. This would result in a diverging thrust range as speed increases. This paper (1) shows the fallacy of this co"cepq (z) demonstrates mathematically and graphically that as speed increases, the tbmst range converges; (3) expresses the need for verification of the calculated data with actual measurements; and (4) discusses potential pump dinnage caused by internal recirculation cavitation at high pumping speeds and the increased exposure to vibration damage resulting from speed variation.The benefits of speed variation.are summarized. A specific ESP was selected as a typical pump for illustration. Data were normalized by dividing all characteristics by those occurring at the "peak efficiency point. The pump performance data thus obtained are used to illustrate techniques 'for designing a pump to be driven at variable or nonstandard speeds. An operating window is presented that is bounded by tie thrust range limits and by the head-vs.-rate curves that correspond to the ,maximum and minimum driving frequencies tO be considered. This is used in the discussion of VSD applications relative to wells of improving productivity and well testing. Also, the pumplmotor mismatch inherent in wide-speed-range applications and resultant low motor efficiency are demonstrated.CoPyright 7987Societyof Petrola"m Enoi"ea,s casing, surface flowline pressure, and completion inter-SPE Production Engineering, February [987 1s

On The Efficiency Of Electrical Submersible Pumps Equipped With Variable Frequency Drives: A Field Study

“…At high frequencies, the pump experiences increased upthrust, which may greatly reduce run life. 4 Also, the entire ESP system is exposed to a wide range of frequencies as the VFD ramps up to its operating level. A large, long ESP may encounter critical vibrations that could easily damage the pump, motor, or protector.…”

The Effect of Speed Variation on the Operating Range of Submersible Pumps

“…It is basically a protector with the thrust bearing mounted on a piston (1). When the pump is operated the shaft is supported by the thrust bearing.…”

“…In addition, the effect of speed on equipment life must be considered. This is discussed in a paper published by the SPE in 1987, 1 The author discusses the theoretical effect of speed on the published operating range of a typical centrifugal pump. He also brings up References and illustrations at end of paper, 397 the point that, for the proper setting of operating ranges, measured pump thrust data is necessary.…”

Role of Artificial Lift in Wells With a Downhole, Flow Control Completion

“…(Powers, 1987) presented the effects of speed variation on the performance and longevity of ESP. (Lee, 1988) describes the algorithm used in this study defining the performance of an ESP lifted well and its subsequent optimization.…”

“…The PIP, defined by the outflow curves, corresponds to the pressure drop in the tubing string and the pump pressure boost at each flow rate. Two electrical frequencies (50 & 60 Hz) are modelled; the higher frequency giving the greatest system performance (Powers, 1987). Figure 7 represents the same data with the node now located at the pump outlet.…”