1ENERGY

The values of the emission factors are determined using the equations presented below.

K Oil − Pmin = 1−

QGas − fuel + QGas − Inj + QGas − flared + QGas − other
QOil − P × GOR

where,KOil-P=

minimum emission factor for oil production (dimensionless)

QOil-P=oil produced (m3/year)

GOR=

gas to oil ratio (dimensionless)

QGas-fuel=quantity of gas used as fuel (m3/year)

QGas-flared=

quantity of gas flared (m3/year)

QGas-inj=

quantity of gas injected back into ground (m3/year)

QGas-other=quantity of gas accounted for in some other manner and that is notemitted (m3/year)

minThe minimum emission is the amount of gas not otherwise accounted for. If no gas is used
as fuel, flared, injected, or otherwise handled, then the minimum emission factor is 1; (i.e.,
all the gas withdrawn from the ground in conjunction with the oil is emitted). If someamount of gas is accounted for, then the minimum emission factor is 1 minus the portion
accounted for.
Emissions also occur due to leaks. The leak emissions are the amount of gas leaked during
various types of handling. If no gas is used as fuel, flared, injected, or otherwise handled,then the leaks are zero. If some amount of gas is managed in these ways, then the leakemission is the amount of gas handled times the leak rate, which is expressed as a fraction.
The following is the equation for the leak emission factor:

KOil−Pleak =KOil-Pleak(QGas− fuel × Lfuel ) + (QGas−inj × Linj ) + (QGas−flared × Lflared ) + (Qgas−other × Lother )QOil−P × GOR= emission factor for leaks in the systems used to handle gas during oil
production

QOil-P= oil produced (m3/year)

GOR= gas to oil ratio; defines the amount of gas produced (in volume) per unitof oil produced (in volume) (dimensionless)

QGas-fuel= quantity of gas used as fuel (m3/year)

QGas-flared= quantity of gas flared (m3/year)

Qgas-inj= quantity of gas injected back into ground (m3/year)

QGas-other= quantity of gas accounted for in some other manner (m3/year)

Lx= leak rates for the handling of the gas in the various ways, expressed as afraction (e.g., 0.01) (dimensionless)

The total emission factor for oil production is then estimated as:

K Oil − P = K Oil − Pmin + K Oil − Pleak

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If none of the gas is controlled or utilised (i.e., Lx = 1 for all x), then the emission factor(KOil-P) is equal to one. This situation occurs when it is not economical to conserve orreinject the gas (e.g., there is no local market for the gas and the volumes are relativelysmall) and when venting of the gas is preferable to disposal by flaring. It is not thennecessary to evaluate the different paths by which CH4 emissions may occur (e.g., fugitiveequipment leaks, process venting, system upsets, etc.) in these cases since the end effect isthe same: essentially all the CH4 produced is emitted to the atmosphere.
Crude Oil Transportation and Refining: The crude oil from production facilities will
initially contain a certain amount of gas in solution. This gas, particularly the CH4 fraction,
evaporates quickly as this oil progresses through the storage and transportation systems
en route to the refinery. When the oil reaches the refinery, it is usually fully weatheredand essentially free of any CH4 .
Accordingly, the basic mass balance relation for oil transportation and refining activities
may be expressed as follows:
EOil-T = QOil-T x F x YF-CH x KOil-T x DF x 10-124where,EOil-T=methane emissions from crude oil transportation and refining (Tg/year)

QOil-T=

oil transported and refined (m3/year)

F=factor defining the amount of gas in solution with the crude oil (per unitof oil by volume) (Dimensionless)

YF − CH4=

methane fraction; the fraction of the gas in solution in the oil that is
methane, on a volume basis, for example, 0.1m3 of methane per 1.0 m3 ofgas. (Dimensionless)KOil-T=emission factor for oil transportation and refining, see below.
(Dimensionless).

DF=density of methane at the temperature and pressure at which F isestimated (g/m3). The relevant temperature and pressure may vary,depending on the values used to calculate F. For example, at 0°C and ata pressure of 1 atmosphere, the density of methane is 715.4 g/m3, and at20°C and 1 atmosphere, the density of methane is 666.6 g/m3.

The first two terms (QOil-T and F) estimate the total amount of gas that is in solution withthe crude oil. The term YF-CH converts the total gas quantity into the quantity of4methane (still on a volume basis). The emission factor (KOil-T) is the fraction of the total
gas in solution that is emitted (at most, KOil-T = 1). To put the emissions estimate on amass basis, DF is used to estimate grams, and the conversion to teragrams follows.
The value of the solution gas factor and the corresponding mole fraction of methane isdetermined by the type of crude oil (light, medium, heavy, or crude bitumen), thecomposition of the associated gas, and the initial vapour pressure of the crude oil when itis placed in the storage tanks or compartments at the production site. Typically, the initialvapour pressure will be equal to the operating pressure of the first vessel upstream of thestorage facilities.
Table 1-59 presents some estimated values for these two parameters at onshore andoffshore facilities. Better estimates may be determined by performing site specific processsimulations.

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ENERGYTABLE 1-59
SOLUTION GAS FACTORS AND CORRESPONDING CH4 MOLE FRACTIONS FOR
DIFFERENT TYPES OF CRUDE OIL PRODUCTION AT ONSHORE AND OFFSHOREFACILITIESType of Crude Oil

Onshore and Offshore Facilities
FSOLUTION GAS FACTOR

YF-CH4MOLE FRACTION

Light

3.3 to 5.0

0.5642Medium

3.2 to 5.0

0.1001

Heavy (Primary)

1.00.8723

Heavy (Thermal)

8.3

0.6666The value of the system adjustment factor is determined using the equation below:

K Oil − T = 1−
QCollected CH4 =QCollected CH4
QOil − T × F × YF − CH4

the amount of methane collected, and not emitted, duringtransportation and refining.

Often this amount is zero
Other terms defined above.
In the absence of any data regarding the volume of CH4 collected, the value of system
adjustment factor should be set to a default value of one.
Exploration and Drilling Losses
Total CH4 emissions from the exploration and drilling sector will usually be small
compared to the amount emitted by other sectors of the oil and gas industry.
Consequently, a simple Tier 1 approach is perhaps most appropriate for use here.
The basic relation is shown below:
ED = Nwells . FD
where,
ED=

total CH4 emissions (Tg) from drilling and testing of oil and gas wells,

Nwells=number of wells drilled and tested, andFD=

average amount of CH4 emitted per well (Tg/well).

Tier 3 - Rigorous Source-Specific Evaluations Approach
Rigorous source-specific evaluations will generally involve compiling the following types ofinformation and may require significant interaction with industry and associated regulatory
agencies:•

detailed inventories of the amount and types of process infrastructure (e.g., wells,minor field installations, and major production and processing facilities),

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