Physical Testing of a High-Speed Helicoaxial Pump for High Gas Volume Fraction Operation

Abstract

High-speed-rotor dynamic pump operation for downhole or surface production is required and also beneficial to handle very high gas volume fraction (GVF) flows. Operating speeds of these pumps can be in excess of twice those of conventional pumps. This study presents results showing that a high-speed helicoaxial pump (HAP) can operate satisfactorily at intake GVFs of up to 98%. The findings increase capabilities of field engineers and operators to boost and maximize production from high gas content wells. The HAPs tested had a 4-in. housing outer diameter (OD) and shaft rotational speed of 6,000 revolutions per minute (RPM). HAP rotor and diffuser clearances were 0.010 and 0.020 in. A water sprayer was included at the HAP inlet. Water volume flow rates were held constant and that for air was varied. Water volume flow rate range was 63 to 143 B/D, and 549 to 3,238 B/D for air. Intake pressures varied from 14 to 76 psig, and average temperature across the HAPs was 20°C. The corresponding measurements were recorded during observed stable pump operation for each test point. The results showed that the HAPs had stable operation during the tests for intake GVF range from 79 to 98%. The range of dimensionless pressure boost (DPB) was between 0.0184 and 0.0501, indicating that at such high speeds, the HAPs were able to add energy to the fluid even at high intake GVFs. For a given intake gas/liquid density ratio, the DPB decreased with increasing intake GVF. For the same liquid flow coefficient and intake GVF, increasing the intake gas/liquid density ratio increased the DPB of the HAP. The higher intake density ratio enhanced the HAP’s capability to provide positive pressure boost up to an intake GVF just above 98%. It was also observed that the HAP with the tighter diffuser-rotor clearance of 0.010 in. had a higher pressure boosting capability than the HAP with 0.020-in. diffuser-rotor clearance. Proper pump intake flow conditioning and homogenization using the water spray facilitated stable operation of the HAPs. Overall and in conclusion, running HAPs at high speeds in addition to optimizing certain features of the HAPs can result in stable pump operation and enhanced pressure boosting in high GVF flows. This study mainly highlights the importance of operating HAPs at high speeds of up to 6,000 RPM. Tightening clearances between rotordynamic components and tailored inlet flow conditioning are also additional features that enhance pressure boosting. This architecture opens up opportunities for field operators and engineering personnel to maximize hydrocarbon production from their very high gas content field assets, thereby increasing the economic bottom line for the stakeholders.