addressing uncertainty in oil and natural gas industry greenhouse

the operations not contained in traditional; “facilities”. Additionally, companies operations tend to
encompass many jurisdictions, which adds to the complexity of compiling an emission inventory.
Therefore, data availability may be different among industry sectors and regions due to a given sector’s
operational considerations and local requirements.
The uncertainty associated with CO 2 emissions from combustion would be primarily attributable to
variation in the composition of combusted fuels and their respective consumption rates (or total volumes).
For quantification of combustion emissions, quality data are typically available for industry facilities in
all sectors, though significant effort may be required in order to collect data for smaller operating
installations that are spread out in multiple locations.
Moreover, since a large fraction of industry operations rely on self-generated, if is the knowledge of the
carbon content of such fuels that is at the root of determining their associated CO 2 emissions. For the
exploration and production sector, the composition of these self-generated fuels may vary with the nature
of the producing formations, while for refining it will depend on the composition of the crude oil
processed and the slate of products manufactured. On the other hand, for natural gas transmission and
distribution operations, gas quality and its composition are expected to adhere to contract requirements
and would vary only within a narrow specifications range. Hence, the use of average fuel compositions
data has to be evaluated when compiling an emission inventory since it might result in wide uncertainty
ranges for some sectors and operations, while they might be perfectly acceptable for others.
A different set of parameters is important for understanding emissions associated with process vents and
fugitive emissions. For many of the large process units that are found in refineries and natural gas
processing plants, numerical models (equations) are available for estimating these emissions. For highpressure
pipelines transmitting natural gas over long distances, the main GHG emissions are due to
reciprocating engines and turbines, venting due to gas blow-down, and fugitive emissions associated with
leaking piping components. For low-pressure gas distribution, most of the GHG emissions come from
compressors and leaks from gas distribution mains and associated equipment. Quantifying emissions, and
their associated uncertainty ranges, for venting and fugitive emissions in the exploration and production
sector poses a real challenge. These emissions could be quite significant for high-pressure uncontrolled
natural gas production operations or miniscule for controlled oil and associated gas production.
For vented emissions, operators in the U.S., as well as other jurisdictions, typically maintain required
records for reporting (and archiving) gas-venting incidents. However, U.S. reports of “lost and
unaccounted for gas” from natural gas pipelines typically account from both vented and fugitive
emissions. Therefore, disaggregating the data would be required in order to derive a separate average
emission factor for venting incidents only. When it comes to fugitive emissions from equipment leaks,
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