Page 73 - Environmental Control in Petroleum Engineering

Drilling and Production Operations 81

Because of the cost of obtaining fugitive emission data, emission
rates are typically measured carefully at only a few facilities. The data
obtained are then normalized to the number and type of fittings to be
used at other facilities. One such set of generic fugitive emission
factors for a production facility that is based on the number of produc-
tion wells and the gas/oil ratio is given in Table 2-12.
More accurate sets of fugitive emission factors can be based on the
number of valves, connections, fittings, flanges, and similar equipment
at a facility. The estimate for the total fugitive emissions would then
be the sum of the average emissions from each piece of equipment
(Schaich, 1991). Table 2-13 provides a list of average emission factors
for various types of equipment.
Past studies indicate that emission factors such as those given in
Table 2-13 can overestimate emissions by several orders of magnitude.
A more accurate method of estimating fugitive emissions is to measure
how many pieces of equipment are leaking and apply one set of fugitive
emission factors to the components that are leaking and a second set to
the components that are not leaking. A set of these generic fugitive
emission factors is given in Table 2-14. In this table, a fitting is
assumed to leak if the concentration measured by a hand-held analyzer
is greater than 10,000 ppm-v (parts per million by volume).
If a more refined measurement of emission concentration at a piece
of equipment is made, an even more accurate set of fugitive emission
factors can be generated. One such set of factors for three emission
ranges is given in Table 2-15. An even more refined approach would
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Table 2-12
Generic Fugitive Emission Rates for Production Facilities
Emission rate
Number of Wells Gas/Oil Ratio (Ibm/well/day)
<!0 <500 2.56
10-50 <500 1.44
>50 <500 0.09
<10 =>500 6.85
10-50 =>500 2.89
>50 =>500 4.34
Source: from Sheehan, 1991.
Copyright SPE, with permission.