High gas volume fractions (GVFs) decrease the pressure boosting capacity of electric submersible pumps (ESPs). To prevent this, advanced gas handlers, helico-axial-pumps, etc., may be installed upstream of the pump, but these equipment can be expensive. This study presents results of testing different impeller combinations up to 90% intake GVF. The findings present a potential economical option for managing high GVF flows in ESP operation, beneficial to boosting and maximizing production from a field asset.
The pump used was a two-stage, radial-type centrifugal pump with 3.78-inch impeller diameter operating at 3400 RPM. Three impeller pairs were used: P0 (no hole in any impeller blades), P1 (holes only in second stage impeller blades), and P2 (holes in first and second stage impeller blades). Water flow rates were fixed from 75 to 550 barrels per day (BPD), and air flow rates varied to give intake GVFs between 10% to 92% for average fluid temperatures about 25°C. The corresponding differential pressures across the pump were measured and compared to one another.
The results showed that for all impellers, the differential pressure across the pumps decreased with increasing GVF. At 75 BPD, pump P0 attained zero differential pressure at about 72% GVF. The impellers in P1 and P2 were able to extend its operation to reach zero differential pressure at 90% and 90% GVF, respectively. When the liquid flow rate was increased to 275 BPD, the differential pressures in P0, P1 and P2 reached zero at about 36%, 38% and 41%, respectively. Increasing the liquid flow rate even further to 410 BPD, results in zero differential pressure at about 26%, 30% and 29% GVF for P0, P1, and P2, respectively. The general trend is that the GVF at which the differential pressure reaches zero decreases with increasing liquid volume flow rate. At lower liquid volume flow rates, holes drilled in the impeller blades significantly extend the pump's GVF handling capability by homogenizing the flow at the inlet of the centrifugal pump. Since the gas-handling performance of a radial-type pump was enhanced, it may be concluded that the performance will be even more favorable for a mixed-flow or axial-flow pump, especially at higher rotational speeds and intake pressures than in these tests.
This study highlights the importance of pursuing economical alternatives to extend the performance envelope of a centrifugal pump operating in high GVF flows. The findings from this work imply that with appropriate modifications to ESP impellers, their operating envelopes may be increased using cost-effective methods. This opens opportunities for stakeholders to maximize production from field assets with very high-gas content, and increase the economic bottomline for the operator.