Nodal analysis is a technique that was developed by the petroleum industry for production systems' design and optimization. It has bcen used as a tool to that end for some twenty years. Nodal analysis is a comprehensive, yet Simple way of calculating and displaying flowing pressures as functions of production rate and various design parameters like tubing size, gas-lift rate, separator pressure, etc. In this study, nodat analysis is applied to a buried crude ~il/~turagals pipeline and an offshore gas/condensate pipeline. Sensitivity analp are performed using supply pressure, delivery pressure, GOR, inclination angle, line size and liquid loading as parameters. Throughput is plotted versus each of these parameters singly and in combinations. Nodal analysis is defined as the process by which the hydraulic effects of parameter variations are calculated and displayed. In nodal analysis, two parameters or sets of parameters me studied at the same time. The pipeline is divided into two flow strings: the Inflow section and the Outflow section. The "node", from which the method derives it's name, is the delimeter between the two halves. Multiphase PVT, pressure and temperature calculations are performed in both traverses at several flow rates and sensitivity parameter values. The calculations take place in the same direction as the flow in the Inflow section and in the opposite direction in the Outflow segment. The calculated node pressure is plotted for both sections as a function of throughput. The intersections of the Wow and Outflow curves represent the solutions at which the total system operates. Dependent variables, like maximum throughput may be plotted as functions of the sensitivity parameters as well. This graphical approach has several distinct advantages over conventional pipeline simulation methods. Fist, one can visualize the effects of changing the sensitivity parameter values. Second, large numbers of calculations can be performed in a fraction of the time required for conventional pipeline simulation models. Third, the engineer can "read between the lines" of the plotted results to identify trends, thereby eliminating many of the cases that normally would be investigated. Fourth, since the calculations in each section are totally independent from each other, and all curve intersections represent solutions, the engineer may study the effects of any Inflow variation versus any Outflow parameter. The flowing pressure and temperature profiles need to be calculated only once. Fiih, iterations on pressure and temperature are eliminated. These advantages not only enchance the engineer's understanding of the system under investigation, but reduce case study preparation and interpretation time significantly. Because of this innate eficiency, detailed case studies that were formerly beyond the reach of the pipeline engineer, are now feasible. A microcomputer simulation model that can be run on any properly configured desk-top or portable unit was used for this study. The power of the nodal analysis method is demonstrated by its ability to display the results of tens to hundreds of normal multiphase pipeline calculations in a few, easy-to-read plots.
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Hein, Michael A. "Nodal Analysis As Applied to Pipelines And Risers." Paper presented at the PSIG Annual Meeting, Tulsa, Oklahoma, October 1987.
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