Electrical Submersible Pump

Topics: Pump, Pumps, Fluid dynamics Pages: 29 (7786 words) Published: May 3, 2011
Electrical Submersible Pump Analysis and Design
May 30, 2001

Electrical Submersible Pump Analysis and Design

Case Services, Inc.

Case Services’ software provides production optimization for a variety of different methods of artificial lift. This paper discusses the dominant factors in electrical centrifugal submersible pump design and monitoring. Emphasis is placed on three areas: • • • Well inflow performance behavior. Fluid Pressure-Volume-Temperature and phase behavior. Pump equipment performance specifications.

An examination of fluid dynamics within a centrifugal pump provides appreciation for the need to analyze the pump “one stage at a time.” The importance of individual pump testing is also identified. This paper focuses on the three ESP products in the csLIFT suite, csSubmersible, csSubsAnalysis, and csSubsDesign. Methods are proposed by which the pump, motor, producing formation, and fluids are considered a complex system, which can be modeled by csLIFT computer software. csSubsAnalysis and csSubsDesign provide a basis for the prediction of the equilibrium point at which a particular set of equipment might operate under specific well conditions. csSubsDesign permits an analyst to compare a number of designs for desirability. Further discussion illuminates the value of periodic monitoring of electrical centrifugal submersible pump installations with csSubsAnalysis. Methods are proposed by which monitoring can identify changes in operating conditions which could adversely impact pump life.


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Electrical Submersible Pump Analysis and Design

Case Services, Inc.

Centrifugal pumps powered by downhole motors have been used for decades to lift fluids from oil wells. These pumps and their coupled motors are commonly referred to as “Electrical Submersible Pumps” or “ESPs”. In recent years, the meaning of the term “ESP” has become clouded with the application of downhole electric motors coupled to progressive cavity pumps. However, the industry still refers to the more conventional centrifugal pumping equipment using the term “ESP”. This paper outlines some of the classical considerations for analyzing, designing, and monitoring of downhole centrifugal pumps. The term “ESP” is always used as an abbreviation for “downhole centrifugal pump powered by a coupled electric motor”. Experience has shown that proper design and application of ESP equipment rests on three pillars: • • • Understanding the well’s productivity. Understanding the fluid ratios and phase behavior of the fluids produced by the well. Careful analysis of activity in each stage of the actual installed pump.

Failure to accurately model the well’s inflow performance behavior will inevitably result in over-sizing or under-sizing the pump. In the absence of a variable frequency drive for adjusting pump output, this can be disastrous. An oversized pump will “pump the well off”. Typically, a “pump off” condition will trigger a “current underload” shutdown of the motor. The well will remain “down” for a predetermined period of time and then start–up again. This behavior is commonly referred to as “cycling”. Since startups create great strains on motors and pumps, cycling will often lead to premature equipment failure. Conversely, an undersized pump will fail to achieve optimum production. Once this is detected, the equipment may have to be replaced. Regardless of whether the equipment is replaced, an undersized pump will significantly reduce the well’s rate of return (ROR). The types of fluids being pumped, and the response of those fluids to changes in temperature and pressure have a tremendous impact on pump performance. Proper design and monitoring requires an accurate description of the Pressure-Volume-Temperature, and phase behavior of produced fluids. Finally, the pump must be considered as a series of individual stages (or individual pumps). In many cases, each pump stage compresses the...
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