Influence of the presence of an upstream annular liquid film on the wet gas flow measured by a Venturi in a downward vertical configuration

This work is included in an overall study linked to the production of gas from high pressure natural reservoirs. During the extraction of the gas, a liquid phase appears as condensates and water. In many applications the gas volume fraction (GVF) is high and the flow can be considered as a wet gas. The exact metering of the extracted gas necessitates gas/liquid separation. In order to reduce the costs, another solution is to measure the whole flow with a single flow meter. Among the different methods on the market, the use of the Venturi meter is nowadays still widespread. Different empirical correlations based on a Lockhart-Martinelli parameter were proposed to take into account the liquid phase, in the gas flow rate measurement. Nevertheless the accuracy of these correlations is not sufficient for allocation or reservoir monitoring. In fact these correlations do not take into account the influence of the two phase flow characteristics in the pipe upstream of the flow meter. To improve the metering method, a research program based on modelling and experimental tests has been developed by Total, Gaz de France and ONERA. In this paper, experimental results on the influence of the liquid film characteristics on the Venturi pressure drop (Delta P) are presented. Visualizations of the film upstream and inside the Venturi meter are shown. They are completed by film thickness wave amplitude and wavelength measurements. The Delta P measurements indicate that for the same Lockhart-Martinelli parameter, the characteristics of the liquid film have a great influence on the correlation coefficient. A one dimensional model is proposed which evaluates the influence of the different phenomena occurring between the two pressure taps. (c) 2006 Elsevier Ltd. All rights reserved.