Design of Pipelines for the Simultaneous Flow of Oil and Gas

Abstract Measurements were made of pressure drops for oil and gas flowing simultaneously through four to ten inch diameter pipelines. These results were related with data from the literature for one-half to three inch diameter pipelines. Previously published data were used to construct a generalized chart for predicting the type of flow pattern in the pipeline. The flow patterns described are bubble flow, plug flow, stratified flow, wavy flow, slug flow, annular flow, and spray flow. Our experimental data were shown to be consistent with the generalized flow pattern chart. The calculation method proposed by Lockhart and Martinelli for designing two-phase pipelines was shown to be inadequate for larger diameter lines and also for some flow patterns. Modifications of the above method in the form of separate equations for each type of flow pattern are presented. Introduction In recent years there has been an increasing tendency to transport both oil and gas simultaneously through pipeline gathering systems. Trends toward central separator batteries, crude stabilizations, and total well stream processing in distillate type fields have emphasized the need for better information on the effects of liquid flowing along with the gas in pipelines. The many fold increase in pressure drop when liquid is deliberately put into a gas pipeline is illustrated by Van Wingen's data in Figure 1. A look at the mechanism of two-phase flow will explain why pressure drops increase so much. When two phases flow through the same pipe the gas usually flows faster than the liquid. The liquid accumulates in the pipe and reduces the cross sectional area available for gas flow. The pressure loss of a fluid flowing through a pipe is inversely proportional to the fifth power of the pipe diameter. The accumulated liquid in the line has the effect of reducing the diameter. A reduction of 20 per cent in diameter would cause a three fold increase in pressure drop, while a 60 per cent reduction would increase pressure drop one hundred times. At some ratios of gas to liquid flowing, the surface of the liquid is very disturbed. There are many projections of liquid waves or ridges into the gas stream. For a half century studies have been made of the effect of roughness of inside pipe surface on pressure drops. Various friction factor charts taking roughness into account are available.