Performance and Hydrodynamics of a Bent Riser Airlift Pump

Abstract

Airlift pumps are commonly employed in oil and gas operations, utilising the upward motion of a gas-liquid mixture driven by buoyancy and density contrasts. While numerous investigations have focused on their behaviour in vertically aligned straight pipes, the influence of pipe curvature—particularly relevant in directional drilling—has not been extensively explored. This work provides a comprehensive experimental assessment of how bends affect the hydraulic performance and flow dynamics of airlift systems. Five bent riser configurations were tested and compared with a conventional straight riser, with emphasis on variations in bend height and horizontal spacing. The findings reveal that pump efficiency diminishes as the horizontal distance between bends increases or when bends are positioned higher along the riser. Specifically, a 15% reduction in water flow rate occurred when the bend’s horizontal span reached twice the pipe diameter. Additionally, a 6% drop was observed when a bend was introduced at three-quarters of the riser height. The minimum air flow rate required to initiate water lifting also increased when bends were placed above the submergence level. Visual flow analysis further identified cyclic flow behaviour within the bent sections. These insights offer practical guidance for enhancing airlift pump designs in non-vertical geometries, addressing notable gaps in two-phase flow system optimisation.