Flow pattern, holdup and pressure drop data are reported and discussed for gas flow experiments in 25.8 and 51.2 mm I.D. pipes inclined upwards at 1°, 5° and 9.2°, While no liquid flows through the system, a certain amount of liquid circulates within the test section giving it many of the characteristics of two phase pipelines. There are many practical situations where liquid may be introduced, due to operational problems, to a system designed for single phase gas. The amount of liquid retained in a pipe depends upon its angle of inclination and the gas rate. Relatively high gas rates are required to blowout all of the liquid. Although no generalized correlations are proposed in this paper, the data reported clearly demonstrates the adverse effects of retained liquid on pressure loss in gas pipelines.
The objective of this study was to examine the characteristics of gas flow in an upward inclined pipe in which liquid is present, but where there is no net flow of liquid. This situation can occur in a pipeline which has been shutdown and allowed to cool to the point where liquid drops out. The condensed liquid will collect at the low points in the line and the above conditions will occur during a subsequent start-up. The situation may also be approximated by a pipeline in which there is an actual two phase flow, but with a very low liquid-to-gas ratio. At low to medium gas velocities, liquid may accumulate at low points over a period of time in significant quantities. Thus while the actual net flow of liquid could be very small, local liquid-to-gas ratios could be quite large. Another case in which this could occur is where a slug of liquid is introduced into the pipeline as a result of a "kick" from an otherwise dry gas well following a stimulation treatment (e.g. acidizing, fracturing). It is only necessary that the gas velocity be sufficiently low that the liquids are not completely swept through the pipe. This paper describes the results of an experimental study of this condition which has been carried out at the University of Calgary. Results are presented and discussed for flow pattern observations, the equilibrium liquid holdup and pressure drop for various gas rates and angles of pipe Inclination.
All flow tests reported herein were carried out in 24.4 m long (80 ft) test sections mounted on the inclinable trestle of the university of Calgary multiphase flow loop. This trestle can be tilted at angles of up to + 9.2° from the horizontal. Air was used as the gas phase; the liquid phase consisted of a 35°API refined oil. The viscosity of the liquid phase was around 6 mPa.s (6 centipose) at the usual flowing temperature of about 22°C. Tests were performed at three inclination angles, +1°, +5 °, and +9.2° for two pipe diameters, 25.8 (1 in) and 51.2 (2 in) mm I. D.
