addressing uncertainty in oil and natural gas industry greenhouse

The CO 2 emissions are calculated using Equation 5-9:
6
10 scf H2 lbmole H2 lbmole gas 1.13 lbmole CO2 44 lb CO2
tonne
E
CO
= 13,000 × × × × ×
2
year 379.3 scf 4.35 lbmole H lbmole gas lbmole CO 2204.62 lb
2 2
E
= 177,700 tonnes CO /yr
CO2
2
The CO 2 uncertainty is then calculated by applying Equation 4-6 and using the relative uncertainty values.
Urel ( ) = Urel ( ) + Urel ( ) + Urel ( )
Urel
CO
2 2
2 2 2
( )
CO
= 15 + 3.89 + 4 = 16.0%
2
2 2 2
Feedstock rate moles C moles H
Based on the assumptions applied for the H 2 plant emission methodologies, the uncertainty associated with
each of the methods provided in the API Compendium is comparable. In both equations, the aggregated
uncertainty is influenced primarily by the ±15% uncertainty values assigned to the feedstock rate (used in the
first method) and the H 2 production rate (used in the second method).
5.4 Strategic Reduction of Uncertainty
This section addresses the potential need to refine the emission inventory to reduce the uncertainty in the
overall emission estimate. There may be several reasons to do this. In some specific locations, there may be
state or national regulations, or guidelines for voluntary programs that suggest or require an emission
inventory to have uncertainties lower than a certain percentage level. A company may also independently
wish to refine its own uncertainty limits, if it considers the uncertainties too large.
The reader should note that none of the strategies mentioned here are aimed at reducing the actual emissions
of GHGs. That is a separate subject, and while emission reductions are achievable in some cases, they are
beyond the scope of this report. This section focuses on reducing the mathematical and statistical uncertainty
associated with an existing emission inventory.
Once a decision has been made to refine and reduce the uncertainty associated with a given inventory, some
strategic analysis of the major sources contributing to the uncertainty is in order. It is important to know
which sources significantly contribute to the overall inventory. It would make little sense to refine a term
with large confidence bounds, but that contributed very little to the overall inventory. It may also be useful to
have a target uncertainty in mind. For example, if the current total uncertainty is ±50.0 % and the company
wishes to reduce it to ±25.0%, then that target is useful in the analysis. As uncertainties of individual values
in the calculations are examined, values that have uncertainties that are already at or below the 25.0% target,
Pilot Version, September 2009 5-18