UniSim Design PIPESYS Tutorial

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3.2.3 Compare CompressorsThe PIPESYS calculations indicate that when a 1000 hp compressor is used the wellhead pressure is lower than when a 750 hp compressor is used. However, this may not result in an economically significant higher production rate, especially if these pressures are located on the steeper region of the wellhead performance curve. Figure 3.4, Figure 3.5 and Figure 3.6 at the end of this application show the wellhead performance curves for Well A, Well B and Well C, respectively.

These curves can be used to evaluate compressor size that would be most economical for use in a particular pipeline network.Locate 686.7 psia and 753.2 psia on the Well A wellhead curve and you should find that these correspond to flows of 11.1 MMSCFD and 10.8 MMSCFD, respectively. This indicates that the 1000 hp compressor would increase production by less than 5%, over that of the 750 hp compressor.

It is therefore reasonable to conclude that adding compression to the system is worthwhile since both compressors lower the wellhead pressures by a large amount, but the small increase in production may not be enough to justify the choice of the 1000 hp compressor. For this example, assume that economic and engineering considerations favour installing the 750 hp compressor.