Abstract
Gerotors are positive displacement pumps and potential artificial lift options in the oil and gas industry. This study presents the performance characteristics from physical testing of a unique one-stage, equal-walled gerotor pump design operating in oil and oil-air mixtures. The pump was tested at various rotational speeds in a flow loop. The performance results were obtained to ascertain potential design optimizations of the pump before embarking on manufacturing and testing of the field prototype pump.
A physical prototype of a one-stage 400 series gerotor pump, suitable for application in a 5.5-inch casing, was designed, manufactured, assembled, and tested. Mineral oil and air were used as the operating media. For given pump outlet valve settings, the pump rotational speeds were set to 200, 250, 300, and 350 revolutions per minute (RPM). Gas volume fractions (GVF) at the pump inlet were varied from 0% to the maximum the current pump design could handle. For each test point, the corresponding pump parameters were measured. Dimensionless performance plots were established for obtaining pump performance at other flow conditions.
The results showed that pump flow rate decreased with increasing differential pressure, typical of positive displacement pumps. At 200 and 350 RPM, maximum pump delivery is about 190 and 330 barrels per day (BPD) of oil, respectively, at zero differential pressure. The pump can supply flow against a differential pressure of up to about 5.5 psi at 200 RPM and 15 psi at 350 RPM. For the 200-350 RPM speed range, volumetric efficiencies varied from 30% to 73%, whereas the electric power input varied from 145 W to 191 W. When pumping oil-air mixtures, the current gerotor pump design can handle 15% GVF maximum, at 250, 300, and 350 RPM. For certain pump outlet pressures, the total fluid flow rates decreased as the GVF increased to 15%. The volumetric efficiencies at 15% GVF varied from 32% to 53%, for the 300 to 350 RPM speed range, whereas the motor electric power input decreased with increasing GVF up to 15%. In conclusion, increasing the pump rotational speed improves the volumetric efficiency and gas-handling capability of the gerotor pump. These observations will aid in the required design optimization to enhance the performance of the future field prototype gerotor pump.
This study presents the capabilities of gerotors as potential artificial lift alternatives to handle liquid and gas-liquid mixtures for boosting applications in oilfield operations. The technology with additional design optimization can be readily integrated into oilfield equipment architecture. The mechanical simplicity of gerotors and their compactness provides a promising artificial lift substitute that may be implemented for downhole or surface production of liquid or gas-liquid mixtures in the oil and gas industry.
