addressing uncertainty in oil and natural gas industry greenhouse

Table 4-9. Measured Composition Data
Mole% dry January February March April May June July August September October November December
Methane 90.73 91.3 91.37 91.21 94.86 93.97 93.91 94.3 94.45 94.33 94.08 92.85
Ethane 3.83 3.74 4.1 4.16 2.27 2.7 2.81 2.59 2.27 2.3 2.3 2.88
CO 2 3.69 3.24 2.93 2.96 1.32 1.23 0.79 1.13 1.38 1.38 1.4 1.49
Propane 0.9 0.8 0.82 0.88 0.61 0.79 0.66 0.65 0.65 0.65 0.66 0.76
i-Butane 0.11 0.1 0.1 0.11 0.09 0.12 0.09 0.1 0.1 0.1 0.1 0.11
n-Butane 0.14 0.13 0.13 0.13 0.12 0.16 0.15 0.14 0.13 0.13 0.13 0.14
i-Pentane 0.03 0.04 0.03 0.04 0.04 0.05 0.04 0.05 0.04 0.04 0.04 0.05
n-Pentane 0.02 0.03 0.02 0.03 0.03 0.04 0.03 0.04 0.03 0.03 0.03 0.04
C6+ 0.03 0.05 0.04 0.05 0.05 0.07 0.06 0.24 0.05 0.05 0.04 0.08
Total 99.48 99.43 99.54 99.57 99.39 99.13 98.54 99.24 99.1 99.01 98.78 98.4
Table 4-10. Average Composition Calculations
Mean,
mole%
dry Std dev t*s/sqrt(n) U(rel)
U(abs),
mole %
MW
Calculation,
lb/lbmole
U(abs),
lb/lbmole
wt% C
calculation,
wt%
U(abs),
wt%
Methane 93.11333 1.529369 0.971714736 1.04% 0.971715 14.93538 0.1559 64.7728 1.4797
Ethane 2.995833 0.747498 0.474937795 15.85% 0.474938 0.900847 0.1428 4.168007 0.6662
CO 2 1.911667 0.988652 0.62815969 32.86% 0.62816 0.841325 0.2765 1.32982 0.4378
Propane 0.735833 0.100856 0.064080962 8.71% 0.064081 0.324503 0.0283 1.535612 0.1373
i-Butane 0.1025 0.00866 0.005502463 5.37% 0.005502 0.059573 0.0032 0.28521 0.0164
n-Butane 0.135833 0.010836 0.006885023 5.07% 0.006885 0.078946 0.0040 0.377961 0.0206
i-Pentane 0.040833 0.006686 0.004247814 10.40% 0.004248 0.029461 0.0031 0.142025 0.0151
n-Pentane 0.030833 0.006686 0.004247814 13.78% 0.004248 0.022246 0.0031 0.107244 0.0149
C6+ 0.0675 0.055942 0.035544067 52.66% 0.035544 0.058172 0.0306 0.281732 0.1485
Total 99.13417 17.25045 73.00041
Sum uncertainty (abs) 0.350567 1.693261
Sum uncertainty (rel) 2.03% 2.32%
For sample size of n=12, the Student’s t distribution value is 2.201.
Note, the resulting estimates are not rounded to show the comparison.
Pilot Version, September 2009 4-25