The simulation of gas pipeline operations has reached a level of maturity, common in the development of a practical technology, at which the emphasis is changing from seeking solutions to technical problems to seeking to realize the benefits of the solutions which have been found. The problems of integrating the equations of motion, stability of solutions, composition tracking, real-fluid thermodynamics, and real-time operation have been solved to the point that future developments will primarily be concerned with speed and efficiency of execution. The current generation of simulation software, commonly referred to as "models", can accurately calculate the distribution of flows, pressures, temperatures, line packs, and compositions. Such models are available for transient or steady-state flows, and may be executed off-line or, driven by SCADA measurements, in real-time. Such an up-beat description of the current simulation technology should not be taken to mean there are no remaining technical problems. We still need to improve our ability to deal with bad or inadequate data, and to learn to sift the copious (not to say "overwhelming") volume of outputs from simulations so as to present the user with concise, timely results which can be quickly assimilated and applied. But, given the simulation technology that we have in hand, our most pressing problem is the transformation of the simulation tool from a technical specialist's device to an integrated part of the pipeline operation as a commercial system.


Prior to regulations which require non-discriminatory transportation, pipeline companies utilized a traditional gas marketing approach: purchases were made from gas producers, then transported to the local distribution company where a sale was made to the LDC. The LDC in turn sold the gas to residential and commercial consumers, industrial users, and electrical generation plants (Figure 1). At the risk of oversimplification, the process was relatively simple and the focus was on the hydraulics of moving the product. In today's environment, gas producers have many choices of where to sell their product. The producer can sell directly to: a gas pipeline company, an electric utility company, an LDC, an industrial gas consumer, or a gas marketerbroker (Figure 2). Each of these groups can, in turn, establish a transportation contract with one or more pipeline companies to move the product from the wellhead to the consumer. For example, although Enron has no northeast corridor pipeline, Enron supplies gas to Brooklyn Union Gas Company through use of a transportation contract with another pipeline company. Clearly, as the number of potential players in the business has increased, the number of possible combinations of business relationships has increased substantially. Open transportation has presented new business opportunities -- and new risks -- to producers, transporters, and consumers alike.

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