Field Processing of Natural Gas
chosen because of its ready availability. The chiller cools
the high-pressure gas to 0°F to produce a sales gas with
low hydrocarbon dew-point. Glycol is injected to prevent
hydrate formation in the heat exchangers. A beneficial result
of glycol injection is that water is absorbed, yielding a
gas of water dew point no higher than 0°F. Separate
dehydration is not required. Approximate ly 65 bhp
compression duty is required in the refrigeration unit.
The gas contains a finite, though low, H2S content that
must be reduced to pipeline specification of ¼ grain per
100 scf. Amine contacting is chosen.
The gas must be compressed from the low field pressure
of 18 psia to a sales-gas pressure of 700 psia. Reciprocating
compressors are used due to the small volume of gas handled.
Three stages of compression are required to retain reasonable
compression ratios and temperatures in each stage. Amine
treating is done at the second-stage discharge pressure.
The 700-psia condensate is stabilized using a reboiled
tray contactor operating at 400 psia to produce approximately
300 bpd of liquid. This liquid has a vapor pressure of
243 psia at 100°F and is supplied to a pipeline. Fractionation
of such a liquid into its individual hydrocarbon products-­
ethane, propane, butanes, and pentanes plus-is not
economical for such a small product rate. It is common
in the U.S. to pipeline such products to a large-capacity,
central fractionation facility.
The 700-psia residue gas has a heating value of 1119
Btu/scf, and the production rate is 5.26 MMscfd.
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11. How does the gas type or source (gas-well gas,
retrograde condensate gas, or associated gas) affect
its processing?
12. How do production location and quantity of produced
gas affect its processing?
13. Name three basic techniques for NGL recovery.
Problems
1. A gas well in Alberta, Canada, produces 30 MMscfd
of gas with the following composition:
Comp.
N2
CO2
H 2S
Cl
C2
C3
Mol %
0.4
11.6
23.0
64.7
0.2
0.1
Wellhead pressure is 835 psia. The gas must be of
sales quality:
GHV
H2 S
H20
980 Btu/scf, dry ideal gas
0.25 grain/IOOscf
0°F dew-point