Experimental Analysis of Centrifugal Downhole Separators in Boosting Artificial Lift Performance

Abstract

Gas evolution and expansion is a natural phenomenon in oil and gas wells. However, gas is detrimental to pumping artificial lift (AL) systems, causing incomplete pump fillage and reduced pump efficiency in oil wells. Pumping AL systems may also be involved in high GLR applications for 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 a novel centrifugal separator. The setup includes a 31-ft horizontal section followed by a 27-ft vertical section that contains the centrifugal separator. The performance of the separator 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 flowrates and compared to a basic gravity separator without the centrifugal part. The performance and outlet flow stability of the separators are compared. Liquid separation efficiency is a measure of the ratio 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 flowrate. Separation efficiency is close to ideal (100%) for liquid rates up to 500 bpd for both separators. The efficiency slightly reduces at higher liquid rates but stays above 80%. This decline in efficiency is more noticeable for the gravity separator compared to the centrifugal one, 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 gravitational one. 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 deliquefy 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 this efficiency.