Evaluation of Inclined-Pipe, Two-Phase Liquid Holdup and Pressure-Loss Correlation Using Experimental Data (includes associated paper 8782 )

Abstract

A 2-in. (5.1-cm) diameter, 550-ft (168-m) long pipeline was designed andconstructed in a hilly terrain configuration. Two-phase-flow holdup andpressure-loss correlations were evaluated using gas/water data obtainedfrom experiments. Accurate predictions were obtained using the Beggs andBrill correlation and a combination of Beggs and Brill and Guzhov et al.correlations. Introduction Two-phase flow in pipelines located in hilly terrain isencountered in the petroleum industry frequently. Inoilfield gathering systems, two-phase mixtures mustbe transported from the wells to the separationfacility. Because of the problems associated with oiland gas production offshore, it is usually necessaryto have a common pipeline for the liquid and the gasstreams. It is especially important to have gooddesign methods for sizing these pipelines. When designing two-phase pipelines, pressurelosses and liquid holdup must be predicted.The liquid holdup is defined as the fraction of pipe occupied by liquid during two-phase flow. A value ofliquid holdup also is an important considerationwhen designing separation equipment, slug catchers, and pumps. A great deal of research has been conducted inhorizontal and vertical two-phase flow, and severalgood correlations exist for these cases. However, only limited research has been performed in inclinedtwo-phase flow. The main objective of this study was to design andconstruct an experimental facility that could be usedto investigate two-phase flow phenomena in pipelines laid in hilly terrain. The secondary objective of thisstudy was to evaluate several existing correlations forpredicting liquid holdup and pressure losses usingdata obtained from the test facility. Literature Review Several authors have investigated inclined two-phaseflow to some degree. An actual field study of a 16-in.pipeline was conducted by Flanigan in 1958.Pressure drops over various sections of the line weremeasured. He concluded that the inclination of thehills had no effect on the pressure drop and that nopressure recovery existed in the downhill sections.Flanigan's design method included using thePanhandle equation to calculate friction loss and anelevation factor to determine the loss caused byelevation. It is possible that Flanigan's elevationfactor could include some pressure recovery in thedownhill sections. This is because any pressure loss, not accounted for by the friction term, is assumed tobe elevation loss on the uphill side. The overallpressure drop was used in the development of thiscorrelation; consequently, any pressure recovery thatmight have been present is included in the elevationterm. A two-phase inclined flow study was conducted in1967 by Guzhov et al. Their data were taken in 2-in.pipe inclined at angles between 9 degrees fromhorizontal. In development of the correlation, two flowregimes were consideredplug and stratified. A mixtureFroude number and the gas input fraction were usedto predict flow pattern. In stratified flow, there is oneliquid holdup expression for uphill flow and one fordownhill flow. JPT P. 1198^