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Current TUALP Research
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Mechanistic Modeling of ESP Performance for Single-Phase and Gas-Liquid Flows
PI: Holden Zhang, TUALP Director
Objective:
• Develop mechanistic model to predict individual losses and overall performance of ESP based on overall pump geometry for different rotation speed, fluid viscosity and density
• Develop mechanistic model to predict ESP performance under different gas-liquid flow conditions, including gas volumetric fraction, gas density (pressure), liquid viscosity and interfacial tension
Abstract:
Normally only the water performance curve is provided by centrifugal pump manufacturers. Pump performance needs to be predicted for different rotation speed and fluids with different viscosities and densities. Starting from the Euler equation for centrifugal pump, individual losses and overall performance of an electrical submersible pump (ESP) are mechanistically modeled for single-phase liquid flow. The model uses a best match flow rate at which the flow direction at the impeller outlet matches the designed flow direction. When the flow rate is lower or higher than the best match flow rate, the theoretical fluid velocity at the impeller outlet needs to be projected to the flow direction corresponding to the best match flow rate. If the projected velocity is higher than the continuity velocity, the difference may be lost due to recirculation in the impeller. For the friction losses in impeller and diffuser, the friction factors are adjusted considering the flow conditions and geometry of the pump. Losses due to change of flow direction through the pump and leakage are also included in the model. The mechanistic model is continuously improved with better closure relationships and validated with experimental results.
Gas is commonly produced with oil (and water). Accurate prediction of ESP performance for gas-liquid flow is important for production and artificial lift system design and optimization. Assuming gas dispersion in liquid, the gas slippage velocity can be calculated based on the balance of centrifugal force and drag force on a gas bubble in a rotating ESP impeller. Then, the gas void fraction and mixture density in the impeller can be calculated and the ESP boosting pressure can be calculated. This mechanistic model considers effects of gas volumetric fraction, gas density (or density difference between gas and liquid, reflecting pressure effect), bubble size (as a result of turbulence, shear, interfacial tension, etc.), liquid viscosity, rotation speed, and flow rate as well as the pump geometry.
Last updated October 07, 2013