Page 77 - Fundamentals of Reservoir Engineering

SOME BASIC CONCEPTS IN RESERVOIR ENGINEERING 16

correlations 8,13 . This in turn facilitates the calculation of the Z−factor using the method
described above.

In calculating the Z−factor it has been assumed that the non-hydrocarbon components,
carbon dioxide, hydrogen sulphide and nitrogen, can be included in the summations,
equs. (1.16) and (1.17), to obtain the pseudo critical pressure and temperature.

This approach is only valid if the volume fractions of the non-hydrocarbon components
are small, say, less than 5% vol. For larger amounts, corrections to the above
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calculation procedures are to be found in the text book of Amyx, Bass and Whiting . If,
however, the volume fractions of the non-hydrocarbons are very large (the carbon
dioxide content of the Kapuni field, New Zealand, for instance, is 45% vol.) then it is
better to determine the Z−factor experimentally as described in a), above.