Background

Who should bear the cost of transporting liquids and liquefiables in natural gas pipelines? This question is still an unsettled issue within the industry after years of negotiations and volumes of testimony with the Federal Energy Regulation Commission (FERC). The FERC has the basic position that the pipeline companies should not pass on cost to the customer incurred to transport a product which belongs to a third party, while the pipelines and the producers maintain that this question is one to be resolved among themselves. When gas pipelines buy gas from producers often the gas is "wet" or saturated with heavy hydrocarbons. These heavy hydrocarbons are known as liquefiables and drop out downstream to form liquids in the pipelines. If a pipeline company is buying "wet" gas, transportation of the liquids and liquefiables is one of the negotiating points of the gas purchase. If the pipeline company is willing to transport the liquids and liquefiables to a downstream separation facility at a negligible charge or no charge, the gas supply is more easily secured by the pipeline. This ability by the pipelines to transport liquids and liquefiables for the producers was extremely important during the gas shortage in the early 70's. Because of the highly competitive nature of gas buying at that time, companies who could not offer a transportation incentive to the producers had a harder time making gas purchases. Transportation of a producer1s liquids and liquefiables was a great benefit to the producer. It prevented his having to install separation facilities at the wellhead and to construct a separate liquids pipeline. Furthermore pipeline companies had accepted the fact that transporting a producer1s liquids and liquefiables was just an adjunct to the price of the gas. Transportation of the liquids and liquefiables does require some additional expense; however the exact incremental costs has been a subject of debate among producers, pipeline companies and the FERC. Thus came the Engineering question; what is the loss in efficiency due to liquids in a pipelines?

Project Description

Natural Gas Pipeline Co. (NGPL) has completed a series of studies where liquid flow in gas pipelines is simulated in a two-phase flow program. The two-phase flow program was developed in 1974 and is based on the work done by Beggs Brill at the University of Tulsa. The objective of this analysis was to determine the relationship between the amount of liquids in a natural gas pipeline and the Weymouth efficiency of the pipeline. In an effort to assure that the conclusions drawn based on these studies would be valid this analysis was broken into two parts. First, the two-phase flow program was tested against actual data collected by the American Gas Association and presented in project PR-148-ll0. Second, curves were developed to show the change in efficiency compared to changes in the liquid to gas ratio.

Conclusion

It can be concluded that where liquids are present in natural gas pipelines, there will be a decrease in efficiency.

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