Visualization Experiments on the Influence of Wall Wettability on the Liquid Loading in Wells
V.Khosla
G.J.N Alberts
S.P.C. Belfroid
TNO, The Netherlands
K. Veeken
Shell, The Netherlands
L.M.Portela
R.A.W.M.Henkes
Delft University of Technology, The Netherlands
Abstract
In previous experiments in our laboratory, carried out in 2009 and 2010, the effect of a hydrophobic wall on the pressure drop and the liquid loading behaviour was analyzed for a vertical tube with 20 mm diameter. These experiments were performed with stainless steel tubes, without and with hydrophobic coating. For a constant Liquid-Gas Ratio (LGR), the critical gas rate for the onset of liquid loading was approximately halved when the coated was present. As a follow-up of these experiments, visualization experiments have been performed with transparent coated and uncoated tubes at the same scale (20mm) at TNO and at a larger scale (50mm) at the Delft University of Technology.
The goal of these experiments was to determine the influence of the wall wettability on the liquid film behavior in the liquid loading process at two different tube diameters. The focus in this project is to understand the film and droplet dynamics in the near wall region using a high speed camera. For a given liquid flow rate, the gas flow rate was varied from very high, to the minimum in the tubing performance curve and down to loading conditions. An inventory of all morphological structures present on gas-liquid interface is made along with the dynamics that they exhibit.
The morphology of the gas/liquid interface changes drastically along the tubing performance curve (TPC). See figure 1. At high gas velocity, the gas-liquid interface comprises of a high density of ripples or ‘capillary waves’ and very less liquid droplets of small size. With a decrease in gas velocity, density of ripples decreases drastically and ligaments are formed on the interface resulting in a large range of droplets diameters formed by the break-up of these ligaments. The presence of roll waves or ‘disturbance waves’ on the liquid film is dependent on the liquid flow rate. Near the minimum of the TPC gravity starts to be dominant, and a transition from annular to churn-annular flow regime occurs characterized by heavy entrainment and large irregular structures on the interface. Finally, at loading conditions, heavy churning of the film occurs, resulting in a high entrainment of very large droplets from the film to the gas core.
High speed movies/images allow direct measurement of the liquid behaviour, for instance in terms of droplet sizes, velocities, acceleration, frequency of roll waves, etc without the necessity of interpretative techniques such as conductance probes. This allowed the extraction of quantitative data for the liquid behavior, in both the annular and churn-annular flow regimes. The experimental data is compared to existing theoretical models.
In the presentation, an elaborate explanation of the evolution of the gas-liquid interface along the TPC is provided. Film and droplet dynamics involved in the liquid loading process are presented with the help of high speed movies. Furthermore, the differences between the 20mm and 50mm setup will be discussed. Finally, the effect of the wall wettability on the interface behavior will be shown.
(a)Usg = 45 m/s /
(b)Usg = 23 m/s
(c)Usg = 14 m/s /
(d)Usg = 7.5 m/s
Figure 1: Images of gas-liquid interface in an uncoated perspex pipe (50 mm dia) at a fixed liquid superficial velocity, Usl = 0.5 cm/s and varying gas superficial velocities, Usg. Flow direction is from bottom to top. The size of each image is 2.75 cm by 2.75 cm.