Highly accurate data for density measurements are required for engineering
calculations as well for developing equations of state (EOS) for use in the custody
transfer of natural gas through pipelines. The widely used present industry standard, the
AGA8-DC92 EOS, was developed against a database of reference quality natural gas
mixtures with compositions containing less than 0.2 mole percent of the heavier C6+
fraction. With the advances in technology in the late nineties, it is possible to produce
gas from deep and ultra-deepwater of the Gulf of Mexico where the pressures and
temperatures encountered are much higher. Produced gas mixtures have compositions
containing higher percentages of the C6+ fraction. As AGA8-DC92 is a statistical fit
equation developed for one set of conditions, time has come to evaluate its performance
to assess whether it is still viable for gas custody transfer with a new set of conditions
encountered.
A highly accurate, high pressure and temperature, compact single sinker
magnetic suspension densimeter has been used first to determine densities of pure
componentâÂÂs densities for which very reliable data are available. After validating its
performance, the densities of four light natural gas mixtures, containing no C6+ fraction
and two heavy gas mixtures containing more than 0.2 mole percent of the heavier C6+
fraction, were measured. The light mixtures were measured in the temperature range of
250 to 450 K and in the pressure range of 10 to 150 Mpa (1450 to 21,750 psi); the heavy
mixtures were measured in the range of 270 to 340 K and in the pressure range of 3.45 to 34.45 MPa (500 to 5,000 psi). Out of those, the data of only two light natural gas
mixtures have been presented in the dissertation. Data on two heavy mixtures have not
been published due to reasons of confidentiality.
Measured densities of light mixtures, not containing the C6+ fraction show less
than expected relative deviations from the AGA8-DC92 EOS predictions except at low
temperature. The deviation with the recently developed GERG02 EOS was more
pronounced. A force transmission error analysis and uncertainty analysis was carried
out. The total uncertainty was calculated to be 0.105 %.
The data measured as a part of this research should be used as reference quality
data either to modify the parameters of AGA8-DC92 EOS or develop a more reliable
equation of state with wider ranges of pressure and temperature.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/5866 |
| Date | 17 September 2007 |
| Creators | Ejaz, Saquib |
| Contributors | Hall, Kenneth R., Holste, James |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 1198147 bytes, electronic, application/pdf, born digital |
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