This paper presents, for the first time, a theoretical model for the bottomhole gas separation efficiency in Electrical Submersible Pump Installations. The model is based only on fundamental physical principles. New experimental data, collected in a field scale apparatus, and covering a wide range of liquid flow rates, GLRs, pressures and rotational speeds, are also presented. Predictions of the model are verified against the experimental data and limited published field data.

It was detected that, when rotary separators are used, two possible operating regions exist on a map of separation efficiency versus liquid flow rate and pressure. In one region the separator is quite effective and in the other the separator is not effective at all. The transition from the high efficiency zone to the low efficiency zone, in terms of liquid flow rate, is sharp. This behavior has never been reported in the literature before.

The model is simple enough that a small subroutine can be easily written, from the equations presented in the paper, to be included in design and troubleshooting programs for ESP installations. Overall agreement of the model’s predictions with the experimental and field data was good in both high and low efficiency zones.

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