Development And Studies For Optimum Two-Phase Flow In A Natural Gas Gathering System
Authors: Beals T.H. 
Published: December 2007

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This paper is to be presented at the 39th Annual Fall Meeting to be held in Houston, Tex., on Oct. 11–14, 1964, and is considered property of the Society of Petroleum Engineers. Permission to publish is hereby restricted to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Editor of the Journal of Petroleum Engineers or the Executive Secretary. Such abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in JOURNAL OF PETROLEUM TECHNOLOGY or SOCIETY OF PETROLEUM ENGINEERS JOURNAL is granted on request, providing proper credit is given that publication and the original presentation of the paper.
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Abstract
Abnormally high pressures in a certain natural gas gathering system are caused by liquid hydrocarbon accumulations. Direct measurements of the magnitudes of these pressures were made on a particular pipe line in this area. Flow calculations, using an existing two-phase flow formula, produced results which are compared with the actual pressures obtained.
Also, the effectiveness of a pigging operation on the same pipe line was determined. Results of this procedure are presented in graphic form.

Introduction
Natural Gas Pipeline Company of America purchases residue gas near the town of Bridgeport, in Wise County, Texas. It also mom and operates a gathering system which delivers raw gas to a gasoline plant from which residue gas is obtained. This gathering system, which transports production from approximately 500 wells, consists of 415 miles of pipe line ranging in size from 2" in diameter to 20" in diameter. The average daily rate of production is 128,000 Mcf, which increases to a maximum of 146,000 Mcf per day during the colder months.
The contracts between the producers and Natural provide that the gas delivered to the gathering system will be commercially dry. However, it was recognized from the beginning that there would be condensation of water and gasoline in the lines, particularly in the wintertime after the gas reached the temperature of the ground. The amount of this condensation could not be accurately predicted prior to the design of the gathering system, but available gas analyses indicated that it would be considerable. After much study, it was finally decided to size the gathering, lines as if they were to transport dry gas and solve the operating problems due to liquid accumulations when they arose.

EARLY OPERATING PROBLEMS AND THEIR SOLUTION
As was expected, abnormally high pressures developed during the first winter. Although some of the worst of these were due to hydrate formations, in rough terrain liquid accumulations alone caused high pressures at the outer limits of some of the gathering lines. Hydrate formations were eliminated by the injection of alcohol, quantities per season being listed in Table 1.