The majority of Western Siberia oil wells in Russia equipped by electric submersible pumps (ESP). Nowadays the common practice is to operate oil well with ESP as close to its production potential as possible. This strategy allows achieving maximum oil rates and economic efficiency according to Vogel's inflow relationship.
Main limiting factor to decrease BHP and increase well's oil production is an ability of ESP to work with high free gas fraction at pump intake. It is well known that ESP fails to generate pressure drop with high gas fraction at pump intake. However, there is no appropriate mathematical model to account it in ESP design properly.
It is often assumed that ESP works well with gas fraction at pump intake below critical and cannot operate with gas fraction at pump intake above critical. Critical gas fraction varies for different ESP types and manufactures from 25% to 35% and even 50% for ESP with gas handling devices like MVP from Centrilift, AGH or Poseidon from Schlumberger. Using this assumption one can conclude that affinity law should work well for ESP with gas fraction below critical. Nevertheless, it is often observed on wells with high gas fraction that increasing of ESP rotating frequency does not affect BHP and production as it predicted by affinity law.
This paper discusses an approach to describe an abnormal well behavior after frequency change. It shows that correlation for ESP head degradation as in SPE 117414 combined with nodal analysis technique allows to predict well behavior with high free gas fraction. It also allows optimizing energy consumption by ESP by varying ESP rotating frequency. Field cases discussed.