Compositional analysis of natural gas expressed as mol% can be converted into gallons per Mcf (GPM) factors by using the formulas and conversion factors shown in Tables 7, 8 and 9 below.
General Rule: a gallon is a gallon regardless of pressure base.
Formula definitions:
Cf/Mol = number of cubic feet in a Mol (see Note below)
Gal/#Mol = gallons per pound Mol
Gal/Mcf = gallons per Mcf
GPM = gallons per Mcf
PF = pressure base to convert from
PT = pressure base to convert to
Note: The number of cubic feet in a Mol is pressure base sensitive. The standard per the Gas Processors Association is 379.49 cubic feet at a pressure base of 14.696. The formula to convert the standard to a different pressure base is as follows:
379.49 times (14.696 divided by PT)
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Table 7 – the number of cubic feet per Mol at different pressure bases.
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Pressure
Base
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Cf/Mol
Factor
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14.65
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380.68157
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14.696
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379.49000
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14.73
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378.61406
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15.025
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371.18037
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Table 8 – the number of gallons per pound Mol by component.
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Component
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Gal/#Mol
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N2
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Nitrogen
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4.1513
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CO2
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Carbon Dioxide
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6.4532
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H2S
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Hydrogen Sulfide
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5.1005
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C1
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Methane
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6.4142
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C2
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Ethane
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10.1259
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C3
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Propane
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10.4327
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IC4
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Isobutane
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12.3859
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NC4
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Normal Butane
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11.9371
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IC5
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Isopentane
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13.8595
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NC5
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Normal Pentane
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13.7130
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C6+
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Hexane+
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16.3920
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Table 9 – the number of gallons per thousand cubic feet (Mcf) at various pressure bases by component.
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Component
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Pressure Base
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14.65
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14.696
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14.73
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15.025
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N2
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Nitrogen
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10.9049
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10.9391
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10.9644
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11.1840
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CO2
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Carbon Dioxide
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16.9516
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17.0048
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17.0442
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17.3855
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H2S
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Hydrogen Sulfide
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13.3984
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13.4404
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13.4715
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13.7413
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C1
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Methane
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16.8493
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16.9022
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16.9413
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17.2806
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C2
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Ethane
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26.5993
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26.6828
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26.7445
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27.2801
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C3
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Propane
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27.4054
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27.4915
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27.5551
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28.1069
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IC4
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Isobutane
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32.5361
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32.6383
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32.7138
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33.3689
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NC4
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Normal Butane
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31.3573
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31.4557
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31.5285
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32.1599
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IC5
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Isopentane
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36.4070
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36.5213
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36.6058
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37.3389
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NC5
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Normal Pentane
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36.0222
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36.1353
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36.2189
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36.9442
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C6+
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Hexane+
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43.0596
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43.1948
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43.2948
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44.1619
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Formulas:
(Mol% divided by 100) times Gal/Mcf = GPM
[(Mol% divided by 100) divided by Cf/Mol] times 1000 times Gal/#Mol = GPM
Calculation Examples:(assumes 11.25 Mol% for ethane (C2) and a pressure base of 14.73).
(11.25% divided by 100) times 26.7445 = 3.0088 GPM C2
[(11.25% divided by 100) divided by 378.61406] times 1000 times 10.1259 = 3.0088 GPM C2