addressing uncertainty in oil and natural gas industry greenhouse

Table F-4. Natural Gas Composition
CO 2
N 2
CH 4
C 2 H 6
C 3 H 8
C 4 H 10
Fuel
Mixture
Mole %
12.0
2.1
80.0
4.2
1.3
0.4
Uncertainty
%
4
4
4
4
4
4
MW
44.01
28.01
16.04
30.07
44.10
58.12
Mole%
×MW
5.28
0.588
12.8
1.26
0.573
0.232
100 MW mixture
20.77 lb/scf
Uncertainty
%
4
4
4
4
4
4
Carbon
Content
(wt%C)
6.94
0
46.3
4.86
2.26
0.925
±2.69% lb/scf 61.24
(lbC/lb total)
Uncertainty
%
4.82
4.82
4.82
4.82
4.82
4.82
±3.71%
(lbC/lb total)
For simplicity, we assume a 4% uncertainty on the mole% for all of the natural gas components. In reality,
the uncertainty of the gas composition should be determined through multiple samples, as shown in
Section 4.
Uncertainty Estimate of the Fuel Mixture Mole %:
The relative uncertainty of the mole% × MW for the individual components is the same as the relative
uncertainty for the mole%, since multiplication by a constant does not change the relative uncertainty. The
uncertainty for the sum of the mole% × MW is calculated by applying Equation 4-4 and using the absolute
uncertainties.
∑
U ( abs) = U( abs)
∑(mole%×MW)
2
mole%×MW
2 2 2
(0.04× 5.28) + (0.04× 0.588) + (0.04×
12.8)
U ( abs) = = 0.558
∑ (mole%×MW) 2 2 2
+ (0.04× 1.26) + (0.04× 0.573) + (0.04×
0.232)
0.558
Urel ( ) = × 100% =± 2.69% lb/scf
∑(mole%×MW)
20.77
( )
The uncertainty for the wt% C for the individual components is calculated by applying Equation 4-6 and
using the relative uncertainties.
wt%C
2 2 2 2
mole%
∑ (Mole%×MW)
( )
Urel ( ) = U( rel) +U( rel) = 4 + 2.69 =± 4.82% wt% C
The uncertainty for the sum of the wt%C is calculated by applying Equation 4-4 and using the absolute
uncertainties.
Pilot Version, September 2009 F-4