Experimental study and mechanistic modeling of pressure surging in electrical submersible pump

Abstract

Gas entrainment is frequently encountered in crude oil production with electrical submersible pumps (ESP). Previous studies revealed that the increase of gas entrainment rate in ESPs results in mild degradation of boosting pressure followed by a drastic drop. This critical condition, termed as pressure surging, significantly affects ESP's operational stability and run-life. In this paper, the pressure surging phenomenon in ESPs is studied through experimental measurements and mechanistic modeling. A 7.62-cm two-phase flow loop with a 14-stage radial-type ESP is used for testing pump performance under single- and two-phase flow conditions. The stage-by-stage boosting pressure with different gas entrainment rates is measured. Effects of intake pressure, gas volumetric fraction (GVF) and rotational speeds on the ESP two-phase pressure increment are investigated. Experimental results show that the boosting pressure of ESP under gassy flow conditions varies significantly with inlet GVFs and fluid properties. For low GVFs (<6%), the ESP pressure increment deteriorates gradually with the increase of gas flow rate. However, severe degradation of pump boosting pressure is observed if the inlet GVF exceeds a certain value (>7%), which triggers ESP's unstable operations. A mechanistic model based on the critical bubble diameter in rotating multiphase flow field is developed to predict the surging initiation in ESPs. Compared with experimental results, the model predictions demonstrate good agreement.