Gas Effect in Electrical-Submersible-Pump-System Stage-by-Stage Analysis

One of the main problems regarding the use of the artificial-lift method of electrical-submersible-pump (ESP) systems is the presence of gas in the pump. This paper presents and describes an analysis of ESP systems with a stage-by-stage calculation to determine intake and discharge pressures to adjust total dynamic head (TDH) for each stage of the pump. The modeling was designed to acknowledge free gas in the pump, and iterative calculations are applied to recalculate, for each stage, fluid characteristics and physical properties, such as viscosity, density, formation volume factor (FVF), surface tension, solubility ratio, gas/oil ratio (GOR), and other flow characteristics along the tubing, such as temperature and pressure. Developed modeling validation was achieved by comparisons in two scenarios. In the first one, fixed values of intake pressure and changeable values of GOR were used to assess gas effect. In the tests for the second scenario, fixed values of GOR and changeable values of intake pressure were used. Necessary research was conducted through a developed computational tool used to size ESP components. The results were different from those obtained with the usual calculations, and it may be implied that the developed modeling is more accurate to determine parameters related to this artificial-lift method. Also, the results were more consistent and closer to the actual behavior of multiphase-flow phenomena within the tubing because each stage has its characteristics individually evaluated. These observations may have an effect on the number of pump stages and influence in choosing the adequate equipment of the system.