The effect of gas injection geometry and an insight into the entrainment and coalescence processes concerned with a stationary Taylor bubble in a downward two-phase flow

Abstract

Suitably formed gas injection geometries permit optimizing the volume of the bubbles created in oil production pipes without recourse to having to change the flow rates of gas. Unfortunately, little research attention has been dedicated to such a study, which may affect the gas lift method of EOR. To address this knowledge gap and to gain more understanding about the coalescence and entrainment processes of the stationary Taylor bubble, an experimental investigation in a bubble drop-down facility using an air–water system was carried out using advanced instrumentation, wire mesh sensor (WMS) and high-speed video photography. The experiments were performed in a 67 mm internal diameter pipe on a stationary Taylor bubble in a downward liquid flow using three different gas injection geometries. Taylor bubble length, the gas and liquid flow rates approaching the stationary bubble were varied. Also, the wake length below, the stationary bubble was measured at different conditions, of gas and liquid superficial velocities and comparisons were made with existing data. A high-speed camera was used to obtain video images of the flow to validate the measurements taken on the wake lengths. Also, the WMS was placed at two different positions, below the gas injection point to obtain time and cross-sectionally resolved information about the spatial distribution of the flowing phases. This information was used to produce time-averaged void fraction, bubble size distribution and contour plots of the two-phase flow structure. Probability density function (PDF) of void fraction of the wake section of the stationary bubbles showed that the flows are in the bubbly flow region whereas the PDF of void fraction for the entire slug unit depicted a typical twin-peaked slug flow. The results of the measurement of Taylor bubble lengths and the corresponding wake of the bubble lengths showed a good match against current published works. The results revealed that the bubble wake length depends on both the nature of the fluid and the pipe diameter, while on the contrary, the bubble length mainly depends on the gas superficial velocity.