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Research Papers: Petroleum Transport/Pipelines/Multiphase Flow

Evaluation of “Marching Algorithms” in the Analysis of Multiphase Flow in Natural Gas Pipelines

[+] Author and Article Information
Luis F. Ayala

Petroleum and Natural Gas Engineering Program, The Pennsylvania State University, 127 Hosler Building, University Park, PA 16802lfay@psu.edu

Doruk Alp

Petroleum and Natural Gas Engineering Program, The Pennsylvania State University, 127 Hosler Building, University Park, PA 16802doruk@psu.edu

J. Energy Resour. Technol 130(4), 043003 (Nov 17, 2008) (10 pages) doi:10.1115/1.3000103 History: Received August 30, 2007; Revised August 28, 2008; Published November 17, 2008

Marching algorithms are the rule rather than the exception in the determination of pressure distribution in long multiphase-flow pipes, both for the case of pipelines and wellbores. This type of computational protocol is the basis for most two-phase-flow software and it is presented by textbooks as the standard technique used in steady state two-phase analysis. Marching algorithms acknowledge the fact that the rate of change of common fluid flow parameters (such as pressure, temperature, and phase velocities) is not constant but varies along the pipe axis while performing the integration of the governing equations by dividing the entire length into small pipe segments. In the marching algorithm, governing equations are solved for small single sections of pipe, one section at a time. Calculated outlet conditions for a particular segment are then propagated to the next segment as its prescribed inlet condition. Calculation continues in a “marching” fashion until the entire length of the pipe has been integrated. In this work, several examples are shown where this procedure might no longer accurately represent the physics of the flow for the case of natural gas flows with retrograde condensation. The implications related to the use of this common technique are studied, highlighting its potential lack of compliance with the actual physics of the flow for selected examples. This paper concludes by suggesting remedies to these problems, supported by results, showing considerable improvement in fulfilling the actual constraints imposed by the set of simultaneous fluid dynamic continuum equations governing the flow.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Solution over short increments of pipe

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Figure 2

Marching solution to the end of pipe

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Figure 3

Pressure profiles: single-phase case

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Temperature profiles: single-phase case

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Velocity predictions: single-phase case

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Mass conservation: marching RK method

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Mass conservation: integrated NR method

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Energy conservation: marching RK method

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Energy conservation: integrated NR method

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NR pressure profile: two-phase flow case

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RK pressure profile: two-phase flow case

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NR temperature profile: two-phase flow case

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RK temperature profile: two-phase flow case

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NR gas velocity: two-phase flow case

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RK gas velocity: two-phase flow case

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NR holdup profile: two-phase flow case

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RK holdup profile: two-phase flow case

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Figure 18

Mass conservation: marching RK method

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Mass conservation: integrated NR method

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Mass conservation, mass units: NR method

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Energy conservation: marching RK method

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Figure 22

Energy conservation: integrated NR method

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Figure 23

Energy conservation, energy units: NR method

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