Film-Thickness Distribution for Annular Flow in Directional Wells: Horizontal to Vertical
- R.J. Paz (U. of Tulsa) | Ovadia Shoham (U. of Tulsa)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- June 1999
- Document Type
- Journal Paper
- 83 - 91
- 1999. Society of Petroleum Engineers
- 4.2 Pipelines, Flowlines and Risers, 4.1.2 Separation and Treating, 1.6.9 Coring, Fishing, 4.6 Natural Gas, 5.3.2 Multiphase Flow, 4.1.5 Processing Equipment
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An experimental and theoretical investigation has been carried out on two-phase annular flow in inclined pipes. The study focused on the effect of the inclination angle on the liquid film thickness distribution. A conductance multiprobe instrument was utilized to measure the local liquid film thickness around half of the pipe periphery for inclination angles of 90°, 75°, 60°, and 45° from the horizontal. A simple analytical model has been developed for the prediction of the liquid film thickness at the top and bottom of the pipe. The model is applicable for the entire range of inclination angles, from horizontal to vertical. Good agreement is observed between the prediction of the model and the experimental data collected in this study and from the literature.
Annular flow is one of the most common flow patterns encountered in natural gas wellbores and pipelines. It occurs under conditions of high gas flow rates and low to medium liquid flow rates. The liquid flows as a film around the pipe inner wall, surrounding a high velocity core, which may contain entrained liquid droplets. The interface between the gas core and the liquid film is very wavy, and atomization and deposition of liquid droplets occur through this interface.
Most of the experimental and theoretical studies on annular flow have been carried out either for vertical or for horizontal conditions. Changes in the physical phenomena occur as the inclination angle varies from vertical through inclined to horizontal flow conditions. Under vertical flow conditions, the liquid film distribution is uniform around the pipe inner periphery. As the pipe is inclined from the vertical to off vertical, the film thickness distribution becomes nonuniform. Due to gravity, the liquid phase tends to accumulate at the bottom part of the pipe. This results in a thicker film at the bottom and a thinner film at the top. The nonuniform film thickness distribution becomes more and more pronounced as the pipe inclination angle approaches horizontal. This phenomenon has a significant effect on the liquid holdup and pressure drop in the system and must be accounted for in order to enable proper design of pipelines, wellbores, and separation facilities.
The following is a brief representation of the pertinent literature for annular flow in vertical and horizontal pipes:
Wallis1 and Hewitt and Hall-Taylor2 presented general discussions of annular flow. Earlier models for annular flow were developed by Dukler3 and Hewitt.4 More recently, other models have been published by Hasan and Kabir,5 Yao and Sylvester,6 Oliemans et al.,7 Caetano,8 and Alves et al. 9
The physical mechanisms associated with annular flow have also been studied extensively. Turner et al.10 and Ilobi and Ikoku11 studied the minimum gas velocity required for liquid removal from vertical gas wells. Wallis,1 Henstock and Hanratty,12 Whalley and Hewitt,13 and Asali et al.14 developed interfacial shear stress correlations. The entrainment process was studied by Hanratty and Asali,15 Schadel et al.,16 and Whalley and Hewitt.13
Measurements of the circumferential film thickness distribution for horizontal annular flow were reported by McManus,17 Butterworth,18 and Fisher and Pearce.19 Experimental data on film thickness distribution and pressure drop were acquired by Dallman,20 Laurinat, 21 and Laurinat et al.22 In a later study, Laurinat et al.23 developed a model for film thickness distribution. Jepson24 evaluated the proposed model and found it suitable for use in large diameter pipes. Recently, Williams25 conducted comprehensive studies on the effect of pipe diameter on annular flow in horizontal pipes
Annular flow in small diameter pipes was studied by Luninski et al. 26 In addition to acquisition of experimental data for film thickness variation, an analytical model to predict the film thickness at the top and the bottom of the pipe was presented.
The purpose of this study is to examine the effect of inclination angle on annular flow. This is achieved by an experimental and theoretical investigation of annular flow characteristics in inclined pipes. The entire range of inclination angles, from horizontal to vertical, is considered. Experimental data have been acquired for the liquid film thickness variation with the inclination angle, and a model has been developed to account for the effect of gravity on the film thickness distribution.
Details of the experimental facility used in this study are given by Paz. 27 The following is a brief description of the test facility and the instrumentation.
A schematic description of the experimental test facility is shown in Fig. 1 . The left side shows the metering section of the liquid (water) phase, while the right side shows the metering line for the gas (air) phase. The test section is shown in the middle. It consists of 9-ft (2.74-m) long, 2-in. (51-mm) inner diameter (ID) R-4000 polyvinyl chloride (PVC) transparent pipe. The gas and liquid phases from the respective metering sections are introduced into a mixing tee at the bottom of the test section. The mixture flows upward in the form of annular flow, passes through the conductance multiprobe instrument (CMPI) where film thickness distribution measuraements are taken, and finally exits from the top into an atmospheric pressure tank for separation. The test section is capable of rotating through the entire range of inclination angles.
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