Experimental Comparison of Two Downhole Separators in Boosting Artificial Lift Performance

Abstract Gas evolution and expansion are natural phenomena in petroleum wells. However, gas is detrimental to pumping artificial-lift (AL) systems, causing incomplete pump fillage and reduced pump efficiency. Pumping AL systems may also be involved in high GLR applications for gas well deliquification. It then becomes essential to separate the gas before the pump's intake in these applications to preserve the life of the pump. Various downhole separators with questionable efficiencies are available today. In this study, an automated experimental separation facility is presented and applied to test the efficiency of two downhole separators. The setup includes a 31-ft horizontal section followed by a 27-ft vertical section that houses the separator. The performance of the separators is evaluated at different air (34 - 215 Mscf/d) and water rates (17 - 867 BPD). The multiphase-flow loop is equipped with pressure transducers and control valves for effective flow control. Data acquisition and process control are performed using LabVIEW™. A newly designed packer-type centrifugal downhole separator is evaluated over a wide range of flow rates and compared to a basic gravity-type separator without the centrifugal part. The performance and outlet flow stability of the separators are compared. Liquid separation efficiency is a measure of the fraction of the inlet liquid produced at the tubing return line. Output flow stability is measured by looking at the ratio of standard deviation over the average flow rate. Separation efficiency is close to ideal (100%) for liquid rates up to 500 BPD for both separators. The efficiency slightly decreases at higher liquid rates, but stays above 80%. This decline in efficiency is more noticeable for the gravity separator compared to the centrifugal, and it is sharper for higher gas rates (over 300 SCF/STB). The centrifugal separator provides a more stable output flow rate with less fluctuations compared to the gravity type. Various flow patterns in the separator outlet and the casing are visualized and recorded. With declining rates of production from oil fields and the need to de-liquefy gas wells, efficient artificial lift is necessary. This system provides a unique and novel tool to simulate the dynamics of flow in wellbores and identify the best tools to improve the efficiency.