Thermal Operational Map of an ESP-In-Skid Motor: A CFD Approach

Abstract

The production of oil in offshore wells has used artificial lifting methods in order to maintain or increase production. In this sense, several established methods for onshore production, such as electrical submersible pumping (ESP), have been implemented in offshore scenarios and, as a consequence, new challenges and needing improvements to optimize production in this type of environment had to be faced. Many studies concern the gas-liquid flow inside de pump but avoid include the motor and its thermal management. In this context, this study focused to assess the complex flow around an ESP motor installed in subsea skids on the seabed (Skid-ESP) through the analysis of their operational and geometric conditions using a computational fluid dynamics (CFD) tool. The main question is: is it possible to create a thermal operational map of the motor in function of motor frequency with CFD tools? The Volume-of-Fluid (VOF) model was applied together with a homogeneous heat transfer (shared temperature field among phases) coupled to the heat conduction inside motor. This approach is known as Conjugate Heat Transfer (CHT). The ESP motor is modeled as a homogeneous and isotropic body with constant volumetric heat generation. The flow analysis was performed applying the model on an industrial scale with incompressible oil and gas in in-situ conditions and considering the heat transfer between the fluid mixture and the its boundary conditions (seawater constant temperature of 4°C and variable motor heat flux as function of motor frequency). The motor frequency range considered was between 40 and 60 Hz. Since the model used was 3D, hot spots were observed at the low part of near seal motor side for gas volume fraction above 3.5%. The employed methodology was able to determine the thermal operational map with a 5% average deviation from field data.